Itchen Implementation NEP Scheme Pump testing and associated investigations of the Candover and Alre augmentation schemes, summer 2011
Southern Water Services November 2012
Itchen Implementation NEP Scheme Notice
This document and its contents have been prepared and are intended solely for Southern Water’s information and use in relation to Itchen Implementation National Environment Programme (NEP) Scheme.
Atkins Ltd assumes no responsibility to any other party in respect of or arising out of or in connection with this document and/or its contents.
This document has 260 pages including the cover.
Document history
Job number: 5099146.410 Document ref: 5099146/70/DG/119 Revision Purpose description Originated Checked Reviewed Authorised Date Rev 2.0 Draft for Client comment SJW MB BP PS 24/05/201 JG 2 MB Rev 3.0 Working versions for SJW, JG, MB July2012 update Rev4.1 Draft for EA review and SJW, JG, MB HG, MB BP BP August sign-off 2012 Rev 6.0 Final SJW, BP BP November 2012
Atkins Pump testing and associated investigations of the Candover and Alre augmentation schemes, summer 2011 | Version 6.0 | November 2012
Itchen Implementation NEP Scheme Table of contents
Chapter Pages Executive summary 1 1. Introduction 3 1.1. Context of investigations 3 1.2. Aim of investigations 4 1.3. Specific objectives 4 2. Background 5 2.1. Catchment water uses 5 2.2. Augmentation schemes 7 2.3. Upper Itchen conceptual understanding 9 3. Approach 11 3.1. Hydrological background to 2011 11 3.2. Asset register and survey 11 3.3. Test programme 12 3.4. Monitoring programme 13 3.5. Start-up pumping tests 15 3.6. Pre-test activity 16 3.7. Pipeline model and set-up 18 3.8. Stakeholder engagement 18 4. Results and analysis 20 4.1. Pumping test diary 20 4.2. Borehole performance 21 4.3. Early time aquifer test analysis 23 4.4. Impact of long term pumping on groundwater levels 30 4.5. Impact of long term pumping on river flows 35 4.6. Impact of pumping on ecology 44 4.7. Candover pipeline assessment 45 4.8. Impact of pumping on water quality 48 4.9. Stakeholder engagement 51 4.10. Revised conceptual understanding 52 5. Conclusions & Recommendations 53 5.1. Overview of success of testing programme in meeting project objectives 53 5.2. Asset suitability for support for public water supply 55 5.3. Issues around ecology 56 5.4. Other considerations 56 5.5. Recommendations 57 References 61
Appendices 63 Appendix A. Asset Survey 65 A.1. Data Collection 65 A.2. Site Visit 65 A.3. Desktop Study 65 A.4. Site survey information 69 A.5. Condition Assessment 71 Appendix B. Water Quality Data 113 B.1. Pre-test water quality testing and results 113 Appendix C. Stakeholder Engagement 118
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C.1. Webpage 118 C.2. Frequently asked Questions 120 C.3. Press Release (Draft) 121 C.4. Media Coverage 123 Appendix D. Pipeline modelling 126 D.1. Tables for WANDA 127 D.2. Hydraulic Profile Scenario 1.BMP 138 D.3. Hydraulic Profile Scenario 2.BMP 139 D.4. Hydraulic Profile Scenario 3.BMP 140 D.5. Candover Schematic.pdf 141 Appendix E. Ecological Reporting 142 Appendix F. Section 32 Details 245
Tables Table 2-1 CAMS final resource availability status ...... 5 Table 2-2 CAMS Water Resource Management Units ...... 6 Table 2-3 Public Water Supplies located in the Itchen catchment ...... 6 Table 2-4 Augmentation Licence Returns ...... 8 Table 3-1 Assumed pumping rates for augmentation scheme boreholes ...... 12 Table 3-2 Gauging stations for stream flow monitoring ...... 14 Table 3-3 Outfall water temperature monitoring ...... 15 Table 3-4 Pre-test water quality sampling ...... 17 Table 4-1 Pumping test diary: operational issues ...... 20 Table 4-2 Yield, drawdown and specific capacity of abstraction boreholes ...... 22 Table 4-3 Calculated early time values of transmissivity and storativity for the Alre abstractions ...... 25 Table 4-4 Calculated early time values of transmissivity and storativity for the Candover abstractions ...... 26 Table 4-5 Pre-pumping groundwater levels for 1976, 1989 and 2011 tests ...... 27 Table 4-6 Alre borehole aquifer properties: comparison with previous test results ...... 28 Table 4-7 Candover borehole aquifer properties: comparison with previous test results ...... 29 Table 4-8 Maximum drawdown recorded at observation boreholes close to abstraction sites during the test pumping ...... 32 Table 4-9 Maximum drawdown recorded at observation boreholes during the test pumping ...... 33 Table 4-10 Observation borehole distance to nearest abstraction ...... 36 Table 4-11 Summary of principal regression parameters. The regression parameters highlighted green were those chosen to estimate natural stream flows ...... 38 Table 4-12 Summary of principal regression parameters from the 1979 Candover Pilot scheme pumping tests. Only results for those gauging stations used for both the 1979 pumping tests and summer 2011 pumping tests are presented. Source: Southern Water Authority (1979) ...... 38 Table 4-13 The total volumetric net gain at each gauging station for the pumping period.Note – Easton and Allbrook & Highbridge net gains are based on adjusted estimated natural flows. Where the net gain is less than zero, these are shown as <0, and where they exceed 100% the figures are shown in red...... 42 Table 4-14 The total volumetric net gain at each gauging station for the pumping period. Note: The values shown for Easton and Allbrook & Highbridge use the original (non-adjusted) estimated natural flows. Where the net gain is less than zero, these are shown as <0, and where they exceed 100% the figures are shown in red...... 43 Table 4-15 Bishops Sutton flow gauging results (Source: EA, November 2011) ...... 44 Table 4-16 Candover pipeline test pumping pattern - 19th October 2011 ...... 45 Table 4-17 Flow rates delivered with siphon - Scenario 1 ...... 46 Table 4-18 Flow rates delivered without siphon - Scenario 2...... 47 Table 4-19 Flow rates delivered with siphon up to final air valve - Scenario 3 ...... 47 Table 4-20 Recorded flows during field tests ...... 48 Table 4-21 Water quality sampling programme during 2011 pumping test ...... 48 Table 4-22 Remaining PAH that cannot be attributed to Axford 1A or Wield 3A ...... 51
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Figures Figure 1.1 Study area Figure 2.1 Candover scheme detail Figure 2.2 Candover site plans Figure 2.3 Alre scheme study area Figure 2.4 Alre site plans Figure 2.5 Upper Itchen conceptual understanding Figure 3.1 Long-term groundwater levels showing 2011 in its historic context Figure 3.2 Groundwater responses to rainfall prior to the 2011 pumping test Figure 3.3 Long-term stream flows at River Itchen gauging stations Figure 3.4 Proposed test pumping programme Figure 3.5 Groundwater monitoring locations Figure 3.6 Surface water monitoring locations Figure 4.1 Pump test diary including actual abstraction and other pump activity Figure 4.2 Early time aquifer test analysis: Alre abstractions Figure 4.3 Early time aquifer test analysis: Candover abstractions Figure 4.4 Comparison of antecedent hydrological conditions: 1976, 1989 and 2011 test pumping periods Figure 4.5 Groundwater contours - After 6 days of pumping (29th September 2011) Figure 4.6 Groundwater contours – After 17 days of pumping (10th October 2011) Figure 4.7 Groundwater contours – After 28 days pumping: Maximum drawdown Figure 4.8 Regional comparison of 2011 test maximum drawdown with 1976 and 1989 results Figure 4.9 Groundwater level timeseries at observation boreholes close to the Candover abstractions Figure 4.10 Groundwater level timeseries at observation boreholes close to the Alre abstractions Figure 4.11 Groundwater level timeseries at observation boreholes in the Candover catchment Figure 4.12 Groundwater level timeseries at observation boreholes in the Alre catchment Figure 4.13 Stream flow at Itchen catchment gauging stations during test pumping Figure 4.14 Observed and estimated natural flows at Itchen gauging stations Figure 4.15 Schematic of net gain calculation Figure Location of observation boreholes between Alre scheme abstractions and Cheriton Stream 4.15a Figure 4.16 Borough Bridge: Percentage difference and observed flows relationship Figure 4.17 Observed and adjusted estimated natural flows at Easton and Allbrook & Highbridge Figure 4.18 Net gain analysis during test pumping at gauging stations along the River Itchen Figure 4.19 Bishops Sutton Cress beds EA additional flow gauging locations Figure 4.20 Candover pipeline capacity test – 19th October 2011 Figure 4.21 Change in stream temperature during pumping period
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Itchen Implementation NEP Scheme Executive summary
The Environment Agency’s (EA) Itchen groundwater augmentation schemes have been investigated for their usefulness or otherwise in the management of deficits in the supply demand balance for the Hampshire South Water Resource Zone. These deficits would result from implementation of Habitats Directive Sustainability Reductions on SWS’s Lower Itchen abstraction licences.
The following criteria were investigated to assess the suitability of the schemes as water resource schemes to support flows in the River Itchen and hence support abstraction at Otterbourne:
1. To confirm (or otherwise), whether the augmentation schemes can deliver the licensed quantities;
2. To confirm the net gain in the flow of the River Itchen at Allbrook & Highbridge gauging stations for a prolonged period of operation of the augmentation schemes during low-flow periods;
3. To investigate constraints in the deployable output of each augmentation scheme and to identify whether these could be removed by asset maintenance and/or replacement;
4. To assess the condition of the M&E assets and what will be required to bring them up to the operational reliability and flexibility required of strategic augmentation boreholes used to maintain public water supplies.
The whole of the River Itchen is designated under European legislation as a Special Area of Conservation. The designation recognises the international importance of the chalk stream ecology of the Itchen as a whole, and listed interest features are:
the macrophyte community, salmon, southern damselfly, white clawed crayfish, brook lamprey, bullhead, and otter
In addition to the testing undertaken by Atkins, the EA commissioned the Hampshire and Isle of Wight Wildlife Trust (HIWWT) to monitor the white clawed crayfish and report on the impact, if any, of the testing on the crayfish population in the Candover stream.
The following activities were undertaken in order to assess the suitability of the schemes against the criteria listed above:
Asset survey Pumping tests Ecological monitoring Monitoring of river flows and impacts on watercress beds Net gain analysis Hydrochemical assessment
The major findings of the investigation are:
The assets are in reasonable condition, some works would be necessary to bring the infrastructure up to water industry and Southern Water’s standards;
Pumping tests revealed that the schemes can be pumped at the licensed rates but the Candover scheme has a restriction imposed on the output by the pipeline diameter which reduces output to approximately 27 Ml/d, 9 Ml/d short of the licence. The Alre scheme output falls short of its licensed quantity by approximately 2 Ml/d.
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Abstraction from the Alre scheme has a rapid and significant impact on the flows entering the watercress beds and although there are offtakes from the discharge pipeline for the cress bed operators to use, this means that slightly less water is available immediately in the river and their management of the offtakes is uncontrolled. This NEP study has concluded that the hydrogeological characteristics of the scheme and the impacts on downstream abstraction licence holders means that the Alre scheme cannot be considered as a viable water resource scheme.
The calculated net-gain at Otterbourne is approximately 20 Ml/d for the Candover scheme and 26 Ml/d for the Alre scheme. It is estimated this can be sustained for approximately 8-10 weeks and then the net-gain gradually diminishes, with a sharp decline after a total of approximately 20 weeks.
The findings of the ecological survey, while not detecting a direct impact on the white-clawed crayfish, produce recommendations to undertake surveys in advance of scheme start-up. These recommendations potentially block scheme use if concerns are raised about crayfish health, and require slow ramp up (approximately two weeks) and ramp down of scheme abstraction rates.
It has to be concluded that with the restrictions recommended to the operation of the Itchen augmentation schemes, due to the concerns over the white clawed crayfish population, the schemes as they are configured cannot be reliably utilised to support water resources supply in the Hampshire South Water Resource Zone. The construction of a new pipeline to move the point of discharge further downstream, thus avoiding the reaches where there would be a risk to the crayfish population, would remove this constraint. For the Candover to be operated as a water resource scheme would require further work to agree appropriate regulatory and operational conditions that are beyond the scope of this NEP report.
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Itchen Implementation NEP Scheme 1. Introduction
1.1. Context of investigations Discussions were held between SWS and EA during AMP4 concerning the possible use of the Environment Agency’s (EA) Itchen (Candover and Alre) groundwater augmentation schemes to assist in the management of deficits in the supply demand balance for the Hampshire South Water Resource Zone that would result from implementation of Habitats Directive Sustainability Reductions on SWS’s Lower Itchen abstraction licences.
Various assumptions made following those discussions to inform the 2009 Water Resource Management Plan (WRMP09) and 2009 Business Plan needed to be fully investigated through a combination of field investigations, analysis and interpretation before the sustainability reductions can be fully implemented. Funding for the Itchen Implementation NEP Scheme was approved in Ofwat’s Final Determination.
The Environment Agency’s Itchen augmentation schemes are located in the Candover and Alre valleys to the north-east of Winchester in Hampshire (see Figure 1.1). The Candover scheme was developed and tested during 1976 and the Alre scheme (originally known as the Further Itchen River Augmentation Scheme or FIRAS) was developed in 1984. The intention for the augmentation schemes was that they would abstract water from the Chalk and discharge it to the Candover Stream and River Alre during periods of low flows to improve water quality in the downstream River Itchen. Since the original licensing of the schemes the environmental significance and sensitivity of the area has been formally recognised with the designation of the River Itchen Special Area of Conservation (SAC). One of the species recognised in the designation is the native crayfish. The Site Action Plan (SAP) from the Habitats Directive Stage 4 Review of Consents published by the EA in October 2007 includes proposals for modifications to the Augmentation Scheme abstraction licences to protect this designated species (Section C.2.9 Group VI River Flow Augmentation Licences).
The text from Section C.2.9.2 reads:
In summary, the following licence changes are required for this option:
Modify Candover Scheme licence to include a condition restricting use to Hands Off Flows of 198 Mld at Allbrook & Highbridge or when flows at Riverside Park fall below 194 Mld. Replace condition in Alre Scheme licence with tiered MRF condition with a condition restricting use to Hands Off Flows of 198 Mld at Allbrook & Highbridge or when flows at Riverside Park fall below 194 Mld. Modify Candover Scheme licence to restrict daily abstraction to 20 Mld between 1st May and 31st August. Include conditions in both licences to refer to section 20 operating agreement.
The following conditions should be included in a section 20 operating agreement to ensure that the environmental outcomes are met:
Preparatory actions before use of the schemes such as channel maintenance, weed cutting, ecological monitoring. Gradual build up of abstraction before May and phased turning off of the schemes after August. Monitoring of ecology, groundwater levels and river flows.
The Environment Agency has advised (meeting 05/04/2011, Doc ref 5099146-DG-42) that until such time as the licences are amended in line with the SAP, they will operate the schemes such that:
Both schemes are subject to the current Alre flow triggers: abstraction for augmentation shall not commence until the flow in the River Itchen as measured at the Agency’s flow gauging stations at Allbrook & Highbridge in aggregate is, during periods 1st February to 31st March, at or below 280 Ml/d, 1st April to 30th November, at or below 240 Ml/d, 1st December to 31st January, at or below 300 Ml/d.
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Maximum abstraction from the Candover scheme is restricted to 20 Ml/d from 1st May until 31st August: This condition is to protect the native crayfish population which are sensitive to increased flow velocities, particularly at the stage of their lifecycle that occurs until the end of August. A gradual build up and ramp down of abstraction is achieved. Preparatory actions are undertaken prior to use.
1.2. Aim of investigations The aim of this investigation is to review the assumptions used for the WRMP09 analysis against the results of a new test pumping programme to establish the usefulness or otherwise of the Candover and Alre augmentation schemes as water resource schemes to support flows in the River Itchen, and hence support abstraction at Otterbourne.
1.3. Specific objectives The main purpose of the augmentation scheme investigations was:
1. To confirm (or otherwise), whether the augmentation schemes can deliver the licensed quantities;
2. To confirm the net gain in the flow of the River Itchen at Allbrook & Highbridge gauging stations for a prolonged period of operation of the augmentation schemes during low-flow periods;
3. To investigate constraints in the deployable output of each augmentation scheme and to identify whether these could be removed by asset maintenance and/or replacement;
4. To assess the condition of the M&E assets and what will be required to bring them up to the operational reliability and flexibility required of strategic augmentation boreholes used to maintain public water supplies.
Note that the term deployable output has a specific definition for water resource planning (see UKWIR WR27). In the context of a Water Resource Management Plan (WRMP) it is the output from a source that can be relied on to contribute to the supply-demand balance under the design conditions of “dry” year demands and drought conditions.
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Itchen Implementation NEP Scheme 2. Background
2.1. Catchment water uses A brief summary of the environmental, domestic and industrial demands on the water in the Itchen catchment is provided here.
2.1.1. SAC The whole of the River Itchen is designated under European legislation as a Special Area of Conservation. The designation recognises the international importance of the chalk stream ecology of the Itchen as a whole, and listed interest features are:
the macrophyte community, salmon, southern damselfly, white clawed crayfish, brook lamprey, bullhead, and otter.
(source: http://jncc.defra.gov.uk/protectedsites/sacselection/sac.asp?EUcode=UK0012599 last accessed 08/05/2012)
2.1.2. SSSI The River Itchen is described as a ‘classic’ chalk river, because of the exceptionally species-rich aquatic flora and associated wildlife. The community of aquatic plants known as macrophytes has an important influence on the river in terms of water levels and flow. It is also the dominant in-stream habitat, supporting a nationally important diversity of aquatic invertebrates, including the native freshwater crayfish.
The Itchen valley contains areas of fen, swamp and water meadows supporting vegetation with diverse plant communities, some very species-rich. Habitats adjacent to the river such as semi-natural riparian vegetation, wet woodland and wet grassland, provide habitat for diverse and sometimes rare invertebrates, riverine bird species and also populations of water shrew, otters and water voles. The fish fauna is typical of lowland chalk rivers in the range of species present, although the community has been modified by introductions of farm-reared trout and the removal of other species. Species such as brown trout, salmon, bullhead, eel and brook lamprey are notable elements of the natural fish fauna (EA Test & Itchen CAMS 2006). It is widely accepted that the upper Itchen is one of the best examples of wild brown trout fisheries in the country (EA CAMS 2006).
2.1.3. CAMS The Catchment Abstraction Management Strategy for the River Itchen is provided in the Test and Itchen CAMS (EA 2006). The document states that the next CAMS assessment is due to commence in 2010; a draft has been made available to date (April 2012).
The CAMS final resource availability status for the Itchen is summarised in Table 2-1 and Table 2-2.
Table 2-1 CAMS final resource availability status
Assessment Point & Assessment Point & GWMU Main Catchment Final Water Resource GWMU Name Assessment 1 Cheriton Stream at Sewards Itchen No Water Available Bridge 2 River Alre at Drove Lane Itchen No Water Available 3 Candover Stream at Borough Itchen No Water Available Bridge 4 River Itchen at Easton Itchen No Water Available
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5 River Itchen at Allbrook & Itchen Over Abstracted Highbridge 6 River Itchen at Riverside Park Itchen Over Abstracted 7 River Itchen Total Itchen Over Abstracted
Table 2-2 CAMS Water Resource Management Units
WRMU Number WRMU Description Main Catchment Water Resources Assessment 1 Upper Itchen to Easton Itchen No Water Available 2 Candover Stream to Borough Itchen No Water Available Bridge 3 Lower Itchen from Easton to Itchen Over Abstracted Woodmill
2.1.4. Watercress The watercress industry has been a prominent part of the Itchen valley for over 100 years. Although much reduced in size, the majority of the remaining farms are located in the upper reaches of the River Alre as the cultivation of watercress depends on the reliable supply of large volumes of groundwater and hence the farms are sited where there is naturally high spring flow.
2.1.5. Fish Farming Aquaculture is undertaken in the Itchen catchment for trout rearing, both for consumption and re-stocking purposes.
2.1.6. Agriculture The agricultural sector as a whole uses relatively little water in the catchment. Many farms have their own supply and this water is used for domestic and general agricultural use.
2.1.7. Public Water Supply There are several public water supply sources located in the Itchen catchment; these are summarised in Table 2-3.
Table 2-3 Public Water Supplies located in the Itchen catchment
Public Water Supply Water Resource Management Unit Abstracting from Source (CAMS) Lasham (South East 1 Upper Itchen ‘No Water Available’ Groundwater - Chalk Water) Totford (SWS) 2 Candover ‘No Water Available’ Groundwater - Chalk Easton (SWS) 1 Upper Itchen ‘No Water Available’ Groundwater - Chalk Twyford (SWS) 3 Lower Itchen ‘Over-Abstracted’ Groundwater - Chalk Otterbourne (SWS) 3 Lower Itchen ‘Over-Abstracted’ Surface water - River Itchen Otterbourne & Twyford 3 Lower Itchen ‘Over-Abstracted’ Groundwater - Chalk Moors (SWS) Gaters Mill 3 Lower Itchen ‘Over-Abstracted’ Surface water - River Itchen (Portsmouth Water)
The surface water source at Otterbourne is classified under the EA abstraction charging scheme as a supported source.
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Itchen Implementation NEP Scheme 2.2. Augmentation schemes The Candover and Alre augmentation schemes were designed and constructed to enable the support of flows in the River Itchen through the abstraction of groundwater from the Chalk aquifer. In particular, flows in the middle and lower stretches of the River Itchen were depleted by surface and groundwater abstraction. The river then received effluent from growing populations in the Eastleigh area and water quality was seen to be critically vulnerable during drought summers. Groundwater schemes were therefore developed to pump water from boreholes located in the upper catchments into the Candover and Alre tributaries, thereby augmenting flows along the whole of the main river. These groundwater schemes remain on standby for the most severe droughts and the Environment Agency plans to use them under carefully controlled conditions for ecological support (CAMS 2006).
The effect of pumping groundwater and discharging it directly into the river is to bypass and accelerate the natural seepage or flow of water through the aquifer to springs in the river valley. The time at which groundwater appears in the river can therefore be adjusted to suit the needs of downstream water users but no extra water is created as a result of the scheme. Abstracted water is replenished by rain falling in the following winter and this is reflected by a delay in the recovery of river flows when winter rain starts. The Candover scheme design and original testing in 1976-7 is written up in The Candover Pilot Scheme Final Report (Southern Water Authority, 1979). The Alre scheme (originally FIRAS) design and initial testing is reported in the Further Itchen River Augmentation Scheme, 1984 Test Pumping Analysis (Southern Water, 1985). The full operational testing of the Alre scheme was written up in the Report on the 1989 Test Pumping of the Alre Scheme (Southern Science, 1991).
The planned frequency of operation was once in 10 years and in practice they were fully used during the droughts of 1976 and 1989. Since then abstraction has fallen substantially and water quality has improved due to water company investment and the regulation of discharges from agriculture and industry.
2.2.1. The Candover augmentation scheme
Design The Candover scheme comprises three sites, each with two abstraction boreholes: Axford, Bradley and Wield. The abstracted water flows through a ductile iron pipeline to the major outfall, just downstream of Northington Bridge. A minor outfall was also constructed 800 m further upstream of the major outfall and 250 m upstream of the perennial head of the river. However, the minor outfall is no longer used due to the problem of fish becoming stranded in the stretch of river between the minor and major outfall when the flow is switched off. In addition the bed losses in the section above the major outfall are considerable, making the discharge less effective. Figure 2.1 shows the major elements of the Candover infrastructure and more detailed individual site plans are shown in Figures 2.2a-c.
The Candover scheme was tested extensively during the 1976 drought and found to work well, with net gain being sustained over six months.
Maintenance and operation Regular maintenance, testing and operation are carried out on the Candover scheme by the Environment Agency, including electrical testing which is carried out on a three yearly cycle. Routine testing of the Candover scheme pumps was carried out in March 2011 when all six boreholes were successfully pumped for a short time. A programme of electrical testing and PPM testing was also scheduled and carried out in May/June 2011, prior to the main summer 2011 pump testing described in this report.
Other major refurbishment of the Candover scheme has included the acidisation of Axford and Wield boreholes in 1995 and replacement of pumps (EA internal summary report on Augmentation scheme testing Autumn 1997). However, exact details of the pump specifications following this pump replacement are not currently available.
The Candover scheme was used in 1976 to support flows in the Candover Stream and hence River Itchen. The subsequent use has been infrequent with extended periods of abstraction occurring during 1989, 1990, 1997, 2005 and 2006. Table 2-4 summarises the augmentation returns for both the Candover and Alre augmentation schemes as held by the EA.
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Table 2-4 Augmentation Licence Returns
Year Alre scheme (Ml) Candover scheme (Ml) 1989 10,680 2,400 1990 1,654 1991 1992 1993 1994 1995 36 1996 56 1997 586 343 1998 1999 2000 2001 63 2002 2003 2004 0.03 0.04 2005 327 2006 0.7 1,051 2007 2008 2009 2010 2011
Licence conditions The current licence for the Candover scheme (licence number 11/42/22.3/150, expiry date 31/03/2013) is for the purpose of augmentation of the Candover Stream. It is set for a daily abstraction of 36,000 m3 (36 Ml/d) and an annual abstraction of 5,000,000 m3 (5000 Ml/a). The time period is “all year”.
Site Action Plan (SAP) The Review of Consents undertaken by the Environment Agency resulted in a Stage 4 Site Action Plan (SAP) for the River Itchen SAC.
The SAP for the augmentation schemes states that the schemes are to be used to support the target flow regime. As part of the SAP for the Candover scheme, the EA has stated that, although not currently part of the licence conditions, they will only abstract a maximum of 20,000 m3/d (20 Ml/d) between 1st May and 31st August (Alison Matthews pers. comm. and 124-DI-55_18Apr11_Itchen NEP abstraction and licence details.xlsx, also 603-DI-55_23Apr12_Nat Engl St4 assessment Itchen SAC.pdf). This regime is intended to protect the native crayfish population known to inhabit the Candover Stream. Also, in practice the scheme is not used until the flow conditions set for the Alre scheme at Allbrook & Highbridge (see below) are met.
The text from the Environment Agency’s non-technical summary relating to the proposed modifications to the augmentation scheme abstraction licences states:
“Modify licences to include the hands off flow (i.e. the flow in the river which dictates when abstraction must cease) as a trigger for use of the scheme. Modify Candover Scheme licence to restrict daily limit (of water that can be abstracted) between May and August (inclusive). Secure an operating agreement for both schemes and ensure work is carried out to restore in-stream habitats and implement a monitoring programme for those habitats.”
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It should be noted that although the SAP has been drawn up for the augmentation schemes, no changes to the licences have been carried out as the intention is for the EA to make any changes at the same time as the Southern Water Lower Itchen Licence Reviews are carried out.
2.2.2. The Alre augmentation scheme
Design The Alre scheme has four sites with a single abstraction borehole at each: West End Vale, Ropley Soke, Gilbert Street and Soames Farm. West End Vale and Ropley Soke feed the Bighton Valley (or Drayton) pipeline which discharges to the River Alre at the Drayton cress beds. Gilbert Street and Soames Farm supply the Bishops Sutton pipeline which discharges at the Bishops Sutton cress beds. Figure 2.3 shows the main features of the Alre scheme, and each site is shown in more detail in Figures 2.4a-d.
The Alre scheme was tested during the drought of 1989 and abstraction took place from May 1989 until February 1990. Transmissivity and storativity values calculated during this testing are higher and lower respectively than those for the Candover catchment and these aquifer properties are less suitable for the development of a river augmentation scheme.
Maintenance and operation As with the Candover scheme, regular maintenance, testing and pumping of the Alre abstractions is carried out by the Environment Agency. Electrical testing is also carried out on a three yearly cycle. The Alre scheme includes surge vessels at each borehole and these are pressure tested every year.
In 2011, pipeline air valves were checked and replaced or refurbished prior to the routine testing and the planned pump testing. The implications of this on the test are discussed further in Section 3.3.1.
Other major refurbishment during the Alre scheme’s lifetime includes the re-drilling and acidisation of the Gilbert Street borehole which did not perform as well as the other sites during testing in 1989 and the installation of new switchgear at all the Alre sites.
The Alre scheme was first tested under a full operational test in 1989. Use since then has been infrequent, with usage being reported in 1996, 1997, 2004 and 2006. The Alre scheme has always been used in conjunction with the Candover scheme. The augmentation scheme returns as held by the EA for the Alre scheme are shown in Table 2-4.
Licence conditions The current licence for the Alre augmentation scheme (licence number 32/070, expiry date 31/03/2013) is for the purpose of river augmentation. The licensed volumes are 2333 m3/hr; 56000 m3/d and 5,100,000 m3/a. Specific conditions attached to the licence limit each borehole to 1,275,000 m3/a, 14,000 m3/d, 583 m3/a. In addition abstraction for augmentation shall not commence until the flow in the River Itchen as measured at the Environment Agency’s flow gauging stations at Allbrook &Allbrook & Highbridge in aggregate is, during periods 1st February to 31st March, at or below 280 Ml/d, 1st April to 30th November, at or below 240 Ml/d, 1st December to 31st January, at or below 300 Ml/d.
Site Action Plan The SAP for the augmentation schemes, in addition to the parameters outlined for the Candover scheme, also states that the Alre scheme abstractions should be turned on gradually in order to reduce the impact on native crayfish in the River Alre.
2.3. Upper Itchen conceptual understanding The geology, hydrology and hydrogeology of the Upper Itchen catchment have been previously studied in some detail. A brief summary is included here to set the current investigations in context. However, further detail can be found in the Candover Pilot Scheme Final Report (Southern Water Authority, 1979) and the Report on the 1989 test pumping of the Alre Scheme (Southern Science, 1991).
The River Itchen is fed by the three main tributaries: the Candover Stream, River Alre and Cheriton Stream. The Candover Stream usually rises around Northington during summer months but in wet years it can flow from Preston Candover. In the upper reaches, topographically stepped springs contribute to the flows, sustaining flow during summer months.
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The River Alre contributes the larger proportion of flow to the river Itchen, compared to the Candover and Cheriton streams, due to its large groundwater catchment which extends further eastwards than its surface water catchment (CAMS 2012). The Cheriton Stream drains a larger block of the chalk aquifer than the Candover Stream and flows are generally higher than those in the Candover, especially during high flow periods. The Candover and Cheriton tend to respond to recharge more rapidly and show more seasonal variation than the River Alre.
The Chalk provides a high proportion, up to 99%, of baseflow to the Itchen and tributaries. An area of significant groundwater accretion to the Itchen occurs downstream of where the three main tributaries join and the Easton gauging station. The accretion is attributed to possible outcropping fissure zones, and further downstream, between Easton and the Chalk-Tertiary boundary at Allbrook & Highbridge the accretion is much lower. This is an area where the catchment narrows, crossing the centre of the denuded Winchester anticline and the Zig Zag (Lower) Chalk Formation outcrops, suggesting a geological control on accretion although it is recognised that it may also be attributable to abstraction effects (CAMS 2012).
The major features of the geology and hydrogeology of the Upper Itchen are shown in Figure 2.5. The Alre and Candover catchments both lie almost wholly on the unconfined Upper Chalk. The Upper Chalk aquifer is up to approximately 100 m thick in this area and dips to the west by 1º. The Middle and Lower Chalk outcrop to the East and the South in the Wey and Meon catchments. These are generally considered less permeable than the Upper Chalk.
Representative groundwater contours for the Upper Itchen catchment can be seen on Figure 2.5. The water table reflects the ground surface, which is higher on the interfluves and catchment divides and lower in the river valleys. The regional groundwater flow direction is broadly from east to west, with flow being directed to the River Itchen. However, there are departures from this classic pattern. The Alre groundwater catchment extends approximately 8 km further east than the surface water divide and there is a significant groundwater peak in the vicinity of Medstead (known as the Medstead Mound) which does not correspond with the surface topography. The Medstead Mound has been found to exhibit unusual behaviour that is difficult to fully explain (Southern Science, 1991). It is also one of the main controls of the groundwater patterns in the Alre catchment, and also impacts the Candover catchment, although to a lesser extent. The groundwater levels in the Medstead Mound have small fluctuations which are unusual for a groundwater peak, and it is thought that this may be due to extremely low transmissivities in the area. Perched water levels and observation boreholes showing a response to barometric pressure changes have also been seen around Medstead, further suggesting low transmissivity Chalk. In contrast to the Medstead area, extremely high transmissivity has been found elsewhere in the Alre catchment. It has been suggested that this might be due to a “karstic” fissure system (Southern Science, 1991; Giles and Lowings, 1989; Southern Water, 1985).
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Itchen Implementation NEP Scheme 3. Approach
3.1. Hydrological background to 2011 Following the dry winter of 2010/2011, groundwater levels in the Candover-Alre area were considered to be relatively low and close to the levels recorded prior to the previous extended testing during 1988/1989. It was therefore agreed between the Environment Agency and Southern Water that, unless considerable rainfall fell in the interim, the summer of 2011 would provide good hydrological conditions for a test of the two augmentation schemes to proceed. One of the main aims of the test was to check on the capability of the schemes to support an extended period of abstraction under low groundwater level conditions i.e. with a stressed system. Figure 3.1 shows the long term groundwater levels observed at four boreholes in the observation network for the Candover and Alre catchments. The groundwater levels for winter-spring 2011 are highlighted and compared with those during winter-spring 1989. The 2011 levels are very similar to those experienced in 1989. Figure 3.3 shows long term stream flow for the Itchen catchment with the winter-spring 1976, 1989 and 2011 periods (the years in which the schemes were test pumped) highlighted. The stream flows for 2011 were not as low as for previous drought periods; however stream flows were still considered to be within a suitable range for a test to proceed and very similar to 1989 flows, in particular.
The test start was scheduled for September and prior to the test there was a period of rainfall which halted and slightly reversed the groundwater recession at OB4 Chilton Candover. This is visible in Figure 3.2 which shows groundwater levels at four observation boreholes across the Candover and Alre catchments, along with rainfall at the Bishops Sutton raingauge. It appears that only the Chilton Candover borehole shows a reverse of the recession, whereas at the other observation boreholes it is a flattening of the recession by the August-September period, due to the relatively wet summer. The Chilton Candover observation borehole is located relatively close to the river and so the river response would have a strong influence over the groundwater level in this borehole. In spite of the relatively wet summer, it was agreed to continue with the test as planned as it was expected that the response to rainfall would be of short duration and groundwater would return to recession.
The pre-test hydrological conditions experienced in 2011 were therefore considered to be similar to those for the previous pumping tests, thus allowing direct comparisons between the results of the different tests.
3.2. Asset register and survey A survey of the augmentation scheme assets was undertaken by Atkins mechanical and electrical staff accompanied by Environment Agency MEICA personnel. Information relating to the asset stock and pipeline along with the current safety testing regime was provided by the Environment Agency. The complete asset survey is provided in Appendix A. A summary of the work undertaken and conclusions are provided here.
A site survey was undertaken followed by a desk review of the information provided by the Environment Agency. A condition assessment of each piece of equipment was made and an OFWAT condition and performance grade assigned. The following aspects of the schemes were considered: pumps, valves, pressure vessels, flow meters, panels, kiosks, instruments and outfall structures. The condition of the visually inspected equipment was found to be reasonably good and was not a restriction to the test proceeding. The schemes could not be inspected in their entirety; some equipment, such as pumps, were not lifted and could not be inspected; other equipment could not be assessed due to lack of access.
A high level comparison to Southern Water’s Mechanical Electrical Design (MED) specifications was made to gauge compliance. No significant non-compliance was found in relation to immediate testing needs. In the longer term, however, if the schemes required alignment with Southern Water’s systems, several areas were identified as needing to be brought up to standard. These included alterations to the panels to allow vibration and stator temperature monitoring of the pumps and most significantly installation of telemetry to allow remote operation and monitoring. Several of the sites do not have nearby telephone lines and the Candover sites have little or no mobile signal so may require a wireless solution. In addition variable speed drives should be fitted to improve ramp up and ramp down options.
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Itchen Implementation NEP Scheme 3.3. Test programme The pumping programme was agreed prior to start-up between Atkins, the EA and SWS. The pumping programme was designed to meet the test objectives as set out in Section 1.3, whilst being constrained by several factors. These constraints are discussed below.
3.3.1. Test programme constraints The Alre scheme has a constraint on the licence allowing abstraction to occur only when flows in the Itchen at Allbrook & Highbridge gauging station falls below a trigger level of 240 Ml/d. When the test programme was planned, it was not expected that the trigger level on the Itchen would be met and therefore a Section 32 Test Pumping Consent was obtained. This is discussed in more detail in Section 3.6.
The Candover scheme does not have this type of flow constraint on the licence, but abstraction is limited to 20 Ml/d from May 1st to August 31st to protect the white-clawed crayfish downstream of the Candover major outfall. In practice, this meant that the Candover boreholes could not be switched on until 1st September because the full scheme output is greater than 20 Ml/d.
In addition to these constraints, the operating protocol for the schemes requires the boreholes to be switched on gradually. This is partly to reduce the impact on the white-clawed crayfish in the Candover Stream. The operating protocol states that turning on should take place over a minimum period of one week, with at least two days between significant increases in flow.
There are further constraints on the switching off of the schemes. The operating protocol states that switch off from full output should take place gradually, over a one week period. It must also be taken into account that running the schemes may attract fish further upstream than they would normally be. Therefore, some residual flow to the streams from the augmentation schemes may need to be left until it has been established that no distress to fish or other species would result from complete shutdown of the schemes.
Prior to the test pumping in 2011, the EA MEICA team with responsibility for the maintenance of the augmentation schemes identified a problem with both of the Alre pipelines (Drayton and Bishops Sutton). There was uncertainty about the effectiveness of the air valves on these pipelines which therefore posed a risk to the pipeline. Remedial works to replace the air valves and test each pump had to be carried out by EA contractors before any test pumping could be undertaken. This had to be completed before the scheme could be run at full output and would not be completed until the middle of July 2011.
The test programme also had to allow for the fact that the borehole pumps in the augmentation schemes are fixed speed pumps. The full power pumping rates were assumed as shown in Table 3-1.
Table 3-1 Assumed pumping rates for augmentation scheme boreholes
Scheme Borehole Assumed rate (Ml/d) Candover Axford 1A 3.5 Axford 1B 3.5 Bradley 2A 4.5 Bradley 2B 4.5 Wield 3A 4.5 Wield 3B 4.5 Alre West End Vale 12 Ropley Soke 12 Gilbert Street 12 Soames Farm 12
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3.3.2. Proposed test programme Taking into account all of the above constraints and the aims of the test, a programme was devised including test length, switch on and off dates, pump rates and associated costs. It was accepted that the test shutdown period was difficult to predict and some pumps may have to be left running longer than specified in the programme. The proposed programme is shown in Figure 3.4. The proposed programme included four weeks pumping at full output from all 10 boreholes. Wield and West End Vale would be started on 8th September 2011, followed by Bradley and Gilbert Street on 13th September, Axford on 15th September and Soames Farm on the 19th September. Shutdown would begin with Soames Farm and Bradley on 16th October, followed by Ropley Soke and Wield on 19th October and Axford 1A and West End Vale on 23rd October. Axford 1 B and Gilbert Street would be left running for longer until it was deemed acceptable to stop augmentation.
For information, it is worth noting that the total estimated power costs for this pumping regime were £142,208 at 2011 prices.
3.3.3. Actual test programme With this kind of investigation the actual pumping programme is likely to deviate from the proposed programme. Various issues were encountered during the test, one of which occurred immediately before the test was due to begin. A survey of the white-clawed crayfish population on the Candover Stream downstream of the Candover outfall before the planned start date identified concerns about the health of the population. Further investigation and assessment of the risk to the population delayed the start of pumping by six days, and the order of pump start-up had to be altered. Several other infrastructure issues were also encountered during the test which meant that the abstraction pattern had to be changed. The operational issues encountered during the pumping test are discussed in Section 4.1.
3.4. Monitoring programme The main focus of the monitoring programme was to quantify the net gain in the Itchen due to the augmentation schemes and to establish the extent of the cone of depression due to the abstractions, thus meeting the main objectives of the longer term pumping test. There have already been two intensive investigations into the schemes previously (1976 and 1989) as well as several minor investigations when the schemes have been used. The monitoring programme for the 2011 testing therefore focussed on areas that would specifically aid Southern Water’s understanding of how the schemes could be operated to provide water resource benefits and hence play a part in the mitigation of the Sustainability Reductions. The monitoring programme also had to allow for time and resource constraints associated with the testing programme.
The monitoring programme included data collection by the Environment Agency as well as Atkins. The data types collected were:
- groundwater levels (spot data and continuous monitoring);
- streamflows;
- ecological data;
- rainfall data;
- augmentation borehole levels and flows; and
- outfall flows.
3.4.1. Groundwater level monitoring The observation boreholes used to capture groundwater levels are all currently used by the EA. Figure 3.5 shows the groundwater monitoring locations used during the pumping test. Observation boreholes were selected based on the cones of depression reported from the 1976 and 1989 test pumping. Particular importance was given to the area along the Alre river valley between the abstractions and Alresford and the expected southern extent of the cone of depression around the River Meon. The northern and eastern boundaries of the cone of depression were also of interest as well as the area around the Medstead Mound.
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There are five boreholes in the Itchen area which have EA continuous groundwater level monitoring devices. Atkins also installed 22 continuous groundwater monitoring devices in observation boreholes in the area. In addition to the continuous monitoring locations, 56 other observation boreholes were identified, at which manual groundwater level measurements would be taken by Atkins. Due to the large number of observation boreholes, they were prioritised into four categories, with Very high (two sites), High (10 sites) and Medium (21 sites) priority locations measured in preference to Low (20 sites) priority locations. This can be seen on Figure 3.5. On most visits, 45 of the 56 observation boreholes were measured. A minimum of four sets of manual measurements were obtained:
a baseline, prior to the start of pumping; at the start of pumping, after all abstractions were running; at maximum drawdown, immediately prior to the start of shut-down; and after abstraction had ceased.
The routine monitoring carried out by the EA continued during the pump test period, meaning that additional manual level measurements were obtained at most of the 78 observation boreholes also monitored by Atkins.
3.4.2. Stream flows Monitoring of stream flows was carried out using the existing EA monitoring network, with data summarised as mean daily flows. This included five gauging stations on the River Itchen, the River Alre and the Candover Stream that would show the impact of the augmentation, and one gauging station on the Cheriton Stream which was used as a control. Figure 3.6 shows the gauging station locations and a summary of their details are shown in Table 3-2.
Table 3-2 Gauging stations for stream flow monitoring
River Site name Gauging Station Distance Type downstream from outfall Candover Stream Borough Bridge Crump weir – 5,925 m from installed 1970 Candover outfall River Alre Drove Lane (total) Crump weir – two, 1.5 3,695 m from B and 2.5; installed Sutton outfall 1970 River Itchen Easton Electromagnetic, data 11,480 m from from 1984. B Sutton outfall River Itchen Allbrook & Highbridge Combined station: 28,380 m from crump weir B Sutton outfall (Highbridge, installed 1971) and thin plate weir (Allbrook) River Itchen Riverside Park Ultrasonic, artificial 35,530 m from influences from B Sutton outfall abstraction and discharge, also occasional tidal. Data from 1982. Cheriton Stream Sewards Bridge Crump weir – n/a installed 1970
3.4.3. Ecological data Sections 1.2 and 1.3 describe the aim and specific objectives of the Itchen Implementation NEP Scheme. The main focus was to confirm, or otherwise, the assumptions used for WRMP09 on the contribution that either or both schemes could make to the supply demand balance.
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As an additional component of the NEP investigation, the Environment Agency commissioned the Hampshire and Isle of Wight Wildlife Trust (HIWWT) to undertake ecological monitoring of the Candover Stream and the River Alre before and during the pumping test. The objective of the ecological monitoring was to address concerns of the potential for flow augmentation to have a localised impact on the ecology of the headwaters of these chalk streams and in particular on the important resident population of the internationally endangered white-clawed crayfish.
The HIWWT report on this work (River Itchen SSSI/SAC Flow Augmentation Schemes – Investigation the potential ecological implications of the Upper Itchen flow augmentation schemes: a specific focus on the resident white-clawed crayfish (Austropotamobius pallipes) population is included as Appendix E to this report.
The monitoring undertaken by HIWWT included drift net surveys to assess the effect of increased water velocity upon passive drift of white-clawed crayfish, particularly juveniles, and a range of other key macroinvertebrate groups. Physico-chemical and water quality monitoring was also undertaken. A full description of the ecological monitoring undertaken is given in Appendix E Section 5.
The monitoring was undertaken before the scheduled start of the pumping tests. As noted in Section 3.3.3, this pre-operation survey revealed anomalous behaviour of the crayfish population which meant that the test had to be delayed whilst the cause was investigated further.
3.4.4. Rainfall data Daily rainfall data were collected from the existing EA monitoring network of tipping bucket raingauges (TBR). Three are relevant to the Itchen area: Bishops Sutton, Harestock and Otterbourne. Their locations can be seen in Figure 3.6. Bishops Sutton raingauge is the closest to the augmentation schemes.
3.4.5. Augmentation borehole levels and flows Groundwater levels in the abstraction boreholes as well as the flow meter readings were taken every day during the full output pumping test. This was to ensure that any pump failures, or problems, were picked up as quickly as possible, but also meant that a continuous time series of daily abstraction rate could be constructed as well as measuring the drawdown due to pumping at each borehole. The daily visits were shared by the EA and Atkins on a rota, with EA standby staff covering the weekend visits.
3.4.6. Outfall flows Monitoring at the outfalls had two objectives. At the Candover Major outfall, a water level monitoring device was installed in the stilling well of the crump weir to measure total flow from the Candover scheme. This provided an extra check on the abstraction rates calculated from the individual flow meters, as well as ensuring the total flow did not exceed the licensed quantity. At the Drayton and Bishops Sutton outfalls on the Alre scheme, this was not possible as the flow did not pass over a weir. However, a secondary aim of this monitoring was to capture any temperature changes in the stream due to the addition of augmentation water. To this end, monitoring devices were installed near the outfall at all three locations to measure water temperature as shown in Table 3-3 .
Table 3-3 Outfall water temperature monitoring
Outfall Specific location Approx. NGR of monitoring device Candover Major outfall Approx. 50 m downstream of the 456800, 136750 outfall, on the downstream side of a disused weir. Drayton outfall In the stream bed within 1 m of the 459690, 133310 outfall Bishops Sutton Major outfall In the flow from the outfall 460490, 132280
3.5. Start-up pumping tests As part of the pumping test, at the initial pump switch on, there was an opportunity to obtain extra information about aquifer properties at the individual boreholes to reinforce findings from previous studies. Therefore,
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Itchen Implementation NEP Scheme when each pump was started up several additional, more intensive, monitoring activities were carried out to allow analysis of the boreholes in terms of characteristics and aquifer properties.
Consideration of previous testing indicated that approximately two hours of intensive monitoring should be carried out (starting from pump switch-on) at each location, in order to obtain adequate data to analyse for aquifer properties. Groundwater levels in the boreholes at each site and flow rate information was collected. The majority of these data could not be obtained by automatic devices as there was no facility for telemetry on the abstraction boreholes. The intensive monitoring effort was shared between EA and Atkins staff.
At the Candover boreholes, where the boreholes are paired (e.g. Axford 1A and Axford 1B) and there is considerable interference between the two boreholes, one pump was switched on and both boreholes monitored for a few hours. Then, the second pump was switched on, with monitoring continuing at both boreholes for a minimum of two more hours. Monitoring data at the nearest observation borehole to the site would show the impact of both pumps abstracting simultaneously.
At the Alre scheme boreholes, each borehole and any nearby observation boreholes were monitored for two hours from when pumping began at that borehole.
3.6. Pre-test activity In order for the pumping test to be carried out on the augmentation schemes, various activities had to be carried out by the EA and Atkins in addition to those outlined in the operating protocol, to ensure the test was compliant with relevant legislation and also to minimise impact on the environment. The most significant of these activities was that a Section 32 Test Pumping Consent had to be obtained for the Alre scheme as the licence trigger level was not expected to be met. This allowed the Alre abstractions to be used for testing purposes. The Section 32 request was assembled and submitted by the EA and was approved prior to the start of test pumping. The Section 32 Consent is included in Appendix F.
To minimise the impact of the augmentation water being discharged into the Candover Stream and the River Alre on riparian landowners, in-channel weed cutting was carried out downstream of the outfalls. This was organised and undertaken by the EA.
3.6.1. Additional flow gauging An additional programme of flow gauging was undertaken by the Environment Agency at the Bishops Sutton cress beds in order to understand how the augmentation scheme abstraction was impacting on the flows into the cress beds and also how the cress bed operators were managing the off-takes from the pipeline to support water flow through the beds. Full details of the locations monitored and results are provided in Section 4.5.4.
3.6.2. Water quality analysis The augmentation schemes do not currently have discharge permits and it is unclear what may be required by the Environment Agency in terms of authorisation for the schemes in the future. Consequently there are no prescribed water quality conditions that the discharged waters are required to meet. From an ecological perspective the water temperature, as well as chemical quality, is important and it was decided to ensure a slow ramp up of the borehole pumping to avoid a sudden change in temperature and velocity regime in the river. In order that the test could proceed it was agreed that the Environment Agency would collect and analyse water samples from the augmentation schemes and Atkins would review these analyses as well as historical data held for the sites. Samples were taken at each production site and also from the outfall at Drayton after pumping at West End Vale for a short time. This would ensure that discharging the abstracted water into the Candover Stream and River Alre would not pose a quality problem for the receiving environment.
3.6.3. Pre-test assessment Assessment of water quality samples collected prior to testing was undertaken in the context of EU Freshwater Fish Directive (FWFD), Dangerous Substances Directive (DSD), Water Framework Directive (WFD) and Drinking Water Directive (DWD). See Table 3-4 for sample location and dates.
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Table 3-4 Pre-test water quality sampling
Sample location Date Ropley Soke 18/07/2011 West End Vale 04/07/2012 Gilbert Street 27/07/2012 Soames Farm 03/08/2012 Drayton outfall, West End Vale 12/07/2012 pumping 27/07/2012 Receiving water course at Drayton 27/07/2012 Axford 1A 06/07/2012 Bradley 2B 06/07/2012 Wield 3A 06/07/2012
The complete assessment is given Appendix B and a summary and the recommendations are provided here.
Water quality was assessed under four areas: metals, nutrients, pesticides and Polyaromatic Hydrocarbons (PAH).
3.6.3.1. Metals summary There appear to be slightly elevated metals concentrations (exceedences for DWD and WFD for different metals) at Gilbert Street and Wield 3A. An exceedence at West End Vale was not repeated following a second sample collection. Given that the other sources in the augmentation schemes do not demonstrate similar exceedences, the concentrations would be expected to be adequately diluted by other abstractions and the receiving waters.
3.6.3.2. Nutrient summary There doesn’t appear to be a problem with nutrient concentrations for the groundwater results considered. The addition of groundwater would be expected to dilute nutrient concentrations in the surface water system.
3.6.3.3. Pesticides summary No recent sampling was undertaken for pesticides; however historical sampling at Axford did not indicate any elevated concentrations or exceedences for the pesticides and herbicides analysed for. Hence this is not considered to be of concern.
3.6.3.4. PAH summary Some exceedences of the DWD PAH concentrations have been found for the Candover scheme at individual boreholes. It is thought these are likely to be due to the pipeline lining and jointing materials.
3.6.3.5. Pre-test water quality assessment conclusions Occasional exceedences of parameter limits occurred in the samples considered. These were mainly for metals for groundwater samples and nutrients for surface water samples. The Candover scheme samples show non-compliance with DWD PAH concentrations and it is thought this may be attributable to the method of sealing pipeline joints that would have been in general use at the time of construction. It is considered likely that slightly elevated concentration of these compounds has resulted partly due lack of regular use of the scheme. It is therefore considered likely that the compound concentrations will reduce if the scheme is used and the pipeline is adequately flushed with clean groundwater. In any case the dilution effect due to water from boreholes not showing these elevated PAH concentrations would be such that concentrations at the outfall would be expected to be below DWD limits.
3.6.3.6. Recommendations It is recommended that the schemes are pumped for a prolonged period and abstracted water is monitored at each abstraction borehole and at the end of each pipeline.
Samples should be collected after approximately a week of pumping (a week from the start for each abstraction borehole) and again at approximately weekly intervals.
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Boreholes should be started such that Soames Farm starts first on the Bishops Sutton pipeline to dilute Gilbert Street.
3.7. Pipeline model and set-up
3.7.1. Hydraulic model objective The objective of the hydraulic model is to determine the theoretical capacity of the Candover scheme with all boreholes operating and discharging to the major outfall. A comparison of this with the actual flows recorded during the recent testing will provide an indication of any underperforming elements in the system.
3.7.2. Summary of information used in model and analysis The following information was used for the modelling. This is provided in Appendix D.
Pipeline chainage, elevations, and locations of air valves/vents were obtained from the River Itchen – Preston Candover Augmentation Scheme – Pipeline Survey Drawing (96:648:01) Feb 1996.
Pipework sizes and arrangements on the borehole sites were obtained from as-built drawings.
Pipework sizes of the main pipeline were obtained from the Candover scheme O&M manual.
Pipework material was identified as cast iron from the Candover scheme O&M manual.
Borehole water levels were from the pipeline test.
Borehole pump performance curves were obtained from the Candover scheme O&M manual; these are the originally installed pumps.
Recorded flows at the major outfall and at each borehole (from pipeline test).
Recorded flow of circa 27 Ml/d at the Major outfall (from pipeline test).
3.7.3. Method The computer modelling was undertaken using Deltares Systems’ ‘WANDA’ software with the information from Section 3.7.2.
The water level in each borehole was set to that observed during the testing and the flow rates delivered determined by the characteristic curve of each pump, and the corresponding total head. For the purposes of the modelling the water level in each borehole was assumed fixed.
The model was constructed using the elevations, pipe sizes and fittings losses as identified from the information provided. A roughness of 0.15 mm was used for all pipes, a typical value for cast iron.
At the Major outfall, flow discharges into a chamber from a vertical, submerged bellmouth and then freely discharges from the chamber to the crump weir. The downstream condition was considered as a submerged bellmouth with fixed water level 1.5 m above the pipe invert. Results of the model runs are presented in Section 4.7.2.
3.8. Stakeholder engagement All engagement with stakeholders thought likely to be impacted by the augmentation testing was undertaken by the Environment Agency. The webpages and frequently asked questions statements issued by the EA before and during the test period are provided in Appendix C. In summary the following stakeholder activities were undertaken.
3.8.1. Cress bed growers / owners Visits; discussions about test activity and growers’ activity; follow-up contact during test and during shut- down.
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3.8.2. Domestic / private borehole users Direct contact; letters; Southern Water agreed to provide emergency potable water bowser supplies to private boreholes considered most at risk if the abstraction from the augmentation scheme boreholes had an adverse impact on water levels in the private boreholes. No action was necessary in respect of this during the test.
3.8.3. Parish councils The Environment Agency contacted several local Parish Councils to advise them of the plans to undertake testing of the augmentation scheme during 2011.
3.8.4. Local Stakeholders Local organisations such as Hampshire & Isle of Wight Wildlife Trust and local fishing interest groups were also contacted as well as private landowners where the augmented river flowed through their land. The relevant MPs were also informed.
3.8.5. Media activity A press release was issued by the Environment Agency setting out the reason for the testing prior to the test. A draft copy is included in Appendix D. The Hampshire Chronicle and the Southern Daily Echo covered the story (see Appendix C.4).
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Itchen Implementation NEP Scheme 4. Results and analysis
4.1. Pumping test diary As described in Section 3.3.3, the proposed pumping test programme had to be revised due to a number of incidents. Figure 4.1 shows a summary test diary and the actual abstraction regime during the test. Abstraction began on 14th September 2011 when West End Vale was switched on. By 27th September all available pumps were running. This output was maintained until 25th October, when shut-down commenced. In total, 28 days of full output pumping was carried out. Between 14th September, and the end of analysis on 30th November, 2879.5 Ml of water was abstracted from the 10 boreholes, with a maximum daily abstraction of 70 Ml/d on 6th October. Table 4-1 below describes the operational issues during the test in more detail.
Table 4-1 Pumping test diary: operational issues
Date Operational issue Details Boreholes Period of outage affected 8th September Pre-test monitoring Until the possibility of All six Candover Start-up of the 2011 of the white-clawed crayfish plague could be boreholes Candover scheme crayfish in the ruled out, any extra was delayed by 12 Candover Stream stress on the crayfish days. Wield 3A and showed signs of population, such as the 3B were eventually distress. addition of lower started on 20th temperature September 2011. augmentation water to the stream was considered too risky. Crayfish on the River Alre All four Alre Start-up of the Alre also had to be checked boreholes scheme was before boreholes in that delayed by six scheme could be days to the 14th switched on. September 2011. 21st Soames Farm It was not possible to fix Soames Farm 21st September to September pump failure the pump in-situ, and the end of test 2011 pump had to be lifted on 5th October 2011 so it could be repaired in the workshop. This pump only ran for one week. 21st Air valve failure on In spite of air valve West End Vale West End Vale September the Bighton replacement work prior to & Ropley Soke was off for one 2011 pipeline the test, a problem with day; Ropley Soke an air valve in Bighton on failed on start-up the Bighton pipeline so was off until 27th meant that both September 2011. boreholes serving this pipeline had to be switched off. 23rd Bradley 2A pump The pump had been set- Bradley 2A Bradley 2A was off September was faulty on start- up wrongly after the last for 1 day until it 2011 up maintenance session so had been fixed. that on start-up it did not Once fixed, it was run at a safe flow rate for decided the extra the pump. capacity was not needed (2B was meeting the Bradley flow rate on its own). 24th Wield 3B pump Wield 3B The fault was
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Date Operational issue Details Boreholes Period of outage affected September failed initially thought to 2011 be too severe to fix in-situ, but was eventually fixed on 5th October 2011. The pump was left on until 8th October 2011. 2nd October Gilbert Street Electrical fault Gilbert Street Fixed and put back 2011 pump failed into service on 6th October 2011. 3rd October Air valve leak on A problem with the air Bradley 2B Bradley was shut 2011 the Candover valve at the edge of the down for a few pipeline at Bradley Bradley site. hours whilst problem was fixed. 19th October Candover pipeline A controlled test of the All six Candover 2011 capacity test maximum capacity of the boreholes Candover pipeline was carried out. 25th October Power failure All power to the sites was Bradley 2A, Both sites were re- 2011 around Preston lost. A safety mechanism Bradley 2B, started the same Candover meant means that if this Wield 3A and day, but Bradley all boreholes at happens, the pumps will Wield 3B was not left Wield and Bradley not re-start automatically running as it was failed. when power is restored. due to be shut off on the 25th October anyway.
Pumping test shut-down The augmentation scheme’s protocol states that shutdown of the pumps must be carried out gradually, and if deemed necessary, some residual flow to the rivers must be left in order to reduce stress to fish and allow flow to continue to the Alre cress beds. Therefore, on the Candover scheme, the majority of the pumps were shut down by 27th October 2011 and the smallest Axford pump was left running. This discharged approximately 4 Ml/d into the Candover Stream. Axford was finally switched off on 8th December 2011. On the Alre scheme, a similar approach was taken, but here flow to the cress beds had to continue until groundwater started to recharge. All abstractions except Gilbert Street had been shut down by the 27th October. After a few weeks, it was necessary to reduce the rate at Gilbert Street further to gradually reduce artificial support to the river and minimise the amount abstracted. A temporary Variable Speed Drive (VSD) was installed at Gilbert Street to enable the flow to be reduced on 18th November, and further reduced on 23rd November 2011. Gilbert Street was finally shut down on 10th January 2012.
4.2. Borehole performance The performance of individual boreholes can be measured by the yield and drawdown and the resulting specific capacity. As these parameters will vary during the pumping test, they have been presented for two time periods, one soon after the start of pumping, and one prior to pump shut-down. These are presented in Table 4-2. These parameters are based on daily average pump rates and spot measurements of drawdown, and should be considered indicative only. Furthermore, several of the Candover abstraction boreholes were pumped simultaneously, and the drawdown and specific capacity reflect this.
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Table 4-2 Yield, drawdown and specific capacity of abstraction boreholes
First pumping day Last pumping day Abstraction Date Yield (Ml/d) Drawdown (m) Specific Date Yield (Ml/d) Drawdown (m) Specific borehole capacity (m2/d) capacity (m2/d) West End 15/09/2011 14.8 3.27 4530 26/10/2011 13.7 6.14 2230 Vale Soames 15/09/2011 14.1* 2.31 6100 20/09/2011 13.6 2.99 4560 Farm Ropley Soke 20/09/2011 14.2 1.16 12240 24/10/2011 14.4 3.92 3670 Gilbert St 24/09/2011 12.1 0.75 16130 02/11/2011 12.3 1.84 6680 Axford 1A 28/09/2011 3.5 3.59 110 18/10/2011 2.9 7.05 410 Axford 1B 28/09/2011 3.6 10.95 90 07/11/2011 4.0 13.38 300 Bradley 2A 20/10/2011 10.0 1.34 7460 24/10/2011 10.4 1.42 7320 Bradley 2B 23/09/2011 10.2 3.71 2750 06/10/2011 10.2 4.66 2190 Wield 3A 21/09/2011 10.8 5.24 2060 24/10/2011 10.1 6.33 1600 Wield 3B 22/09/2011 6.8 4.71 1440 21/10/2011 6.1 3.51 1740 From early hours of test as meter readings on subsequent days are uncertain/unreliable
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4.3. Early time aquifer test analysis In order to investigate the aquifer properties at each of the augmentation boreholes, the early time data (yield and drawdown) collected on pump start-up at each site were analysed.
Drawdown measured at the abstraction boreholes as well as a selection of nearby observation boreholes was initially used in the analysis. However, the aquifer properties derived from measurements taken at observation boreholes are considered more reliable than those based on abstraction borehole measurements. This is because fewer of the assumptions of the analysis models (e.g. Theis) are met when used on the abstraction borehole itself. In particular, the methods use a radial distance from the abstraction borehole, which for the abstraction borehole itself would be zero. The aquifer properties reported here are therefore based on observation borehole drawdown measurements.
At the Candover abstraction boreholes, the aquifer property analysis was further complicated by interference effects. Each abstraction site has a pair of pumping boreholes 60 m apart. Interference effects are therefore considerable. Although pump start-ups were staggered, it was not possible to derive reliable aquifer properties from the measurements at each of the two abstraction boreholes separately. Therefore, the analysis here has calculated the cumulative average effect of pumping from both boreholes.
The yield-drawdown data were plotted on a semi-log scale to undertake a Cooper-Jacob analysis, as well as plotted on a log-log scale to carry out Theis and Neuman analyses. The analysis was undertaken using the software AquiferWin32. The results of the pump test analysis provide an indication of transmissivity and storativity of the abstraction boreholes. The analysis is limited by the short test durations and the pump control set-up which meant that a constant flow rate was difficult to maintain. In addition, analysis of the Candover boreholes had to be undertaken on the pairs of boreholes due to the interference effects and the short test duration. Given these limitations, the results should be considered indicative only.
Table 4-3 and Table 4-4 provide a summary of transmissivity and storativity values calculated and the type curve used to derive these. The plots can be seen in Figures 4.2 and 4.3. For each site, an average T and S has been calculated and this is also shown in Table 4-3 and Table 4-4.
4.3.1. Aquifer properties derived
West End Vale At West End Vale, the pump was started on the 13th September 2011. Drawdown measured manually for the first four hours after start-up in the nearest observation borehole (28 m radial distance from the ABH) was analysed for aquifer properties. There was some evidence of a delayed yield response to the pumping, with the drawdown data fitting the Neumann type curve. However, the Theis confined response also fitted the data.
Soames Farm The pump at Soames Farm was started on the 15th September 2011. Drawdown measured with an automatic monitoring device in the nearest observation borehole, 168 m away, was analysed for aquifer properties. There was no clear evidence of delayed yield at this location, but this may be a result of the time period monitoring data are available for and does not necessarily mean that an unconfined response is not found in the aquifer here. For the analysis, the Theis curves were matched to the late time data.
Ropley Soke The pump at Ropley Soke was started on 19th September 2011. Drawdown measurements from the nearest observation borehole (40 m radial distance) were analysed for aquifer properties. There was a pump interruption 1.3 days after pump start-up, thereby limiting the available data for aquifer test analysis. There was some indication of delayed yield in the data from the nearest observation borehole (G3A Ropley Soke). Matching the early data and the late data to the Neumann type curve generated differing transmissivity and storativity results, reflecting the different responses within the aquifer to storage and leakage. The Theis curve can also be used to analyse the data.
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Gilbert Street At Gilbert Street, the pump was started on the 23rd September 2011. However, on this occasion, it was not possible to obtain any manual measurements of drawdown in the abstraction borehole due to problems with the dip tube in the borehole. Unfortunately, the automatic monitoring device installed in the nearest observation borehole (H3 Gilbert St, 5 m radial distance) also failed on this occasion, so no analysis was possible of the initial pump start-up. However, the Gilbert Street pump failed on 2nd October and when it was re-started on the 4th October, the automatic monitoring device was able to capture the drawdown. Although the results will have been affected by the previous pumping here, the drawdown still gives some indication of transmissivity and storativity. There is some evidence of delayed yield at Gilbert Street, although the Neuman analysis produces a lower transmissivity than Theis.
Axford (1A & 1B) The Axford pumps were started on the 27th September 2011. The start-ups were separated by 2.5 hours, but interference is significant and the drawdown seen at the nearest observation borehole (OB1 Axford at 225 m radial distance) is a result of pumping from both boreholes. The drawdown data from the observation borehole did not match any type curve well as a whole. The latter part of the drawdown data shows a reduced rate of drawdown, potentially indicating the effects of delayed yield. The flow measurements taken during the Axford pump start-ups were considered erroneous, and therefore a representative flow rate from combined pumping of the Axford boreholes the following day (28th September 2011) has been used.
Bradley (2A & 2B) The pumps at Bradley were both started on the 22nd September 2011. 2B was started first, with manual measurements taken at 2B and 2A for two hours. Later the same day, 2A was started but was found to be faulty and so ran for less than one hour. The aquifer test analysis has been carried out on drawdown data from the nearest observation borehole (OB2 Bradley at 350 m radial distance) which reflect pumping at 2B and also the short period of pumping at 2A. Drawdown at the observation borehole was measured by an automatic monitoring device for one week from pump start-up. The effects of delayed yield are not clearly seen in the drawdown at OB2 Bradley, and it appears that Theis-type flow is occurring. It is unclear whether this is the early (unlikely as this period of pumping is usually very short) or late part of a delayed yield unconfined response, or whether a confined aquifer response is being seen. In the 1976 test pumping (Southern Water Authority, 1979), a confined Theis-type response was seen at OB2 from combined Bradley pumping, reinforcing the Theis response seen in 2011.
Wield (3A & 3B) The pumps at Wield were both started on the 20th September 2011. Although the start-up was staggered by 90 minutes, the interference from the two pumps was such that the aquifer test analysis has been carried out from the drawdown measurements at the nearest observation borehole (OB3 Preston Drove at 160 m radial distance). This drawdown includes the impact of both abstraction boreholes. Drawdown at the observation borehole was measured by an automatic monitoring device for one week from pump start-up. The available drawdown data appear to show the tail end of a delayed yield response and the later Theis curve of the unconfined aquifer behaviour. However, as the data fit the later Theis curve, it is also possible to calculate aquifer properties from this analysis as well. The storativity value derived from Theis analysis is more realistic than that from the Neumann analysis.
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Table 4-3 Calculated early time values of transmissivity and storativity for the Alre abstractions
Pump rate Beta (for Abstraction Observation Transmissivity Storativity Evidence of delayed (Ml/d) Type curve Neuman borehole borehole (m2/d) (-) (to 2 s.f) yield? analysis) Neuman 3000 0.011 0.1 Theis 4470 0.015 West End Some evidence of delayed 13.5 F4 1, Bighton Rd Vale Cooper & Jacob 5000 0.011 yield.
AVERAGE 4735 0.013
Theis 3520 0.31 Soames No clear evidence of 12.1 Soames Place Cooper & Jacob 8220* 0.11 Farm delayed yield. AVERAGE 5870 0.21 Theis 6300 0.025 Cooper & Jacob 6970 0.017 Some evidence of delayed Ropley G3A Ropley yield as the rate of 13.5 Neuman (early) 930 0.009 1 Soke Soke drawdown changed during Neuman (late) 7070 0.0002 1 the time period. AVERAGE 5317.50 0.013
Neuman 1050 0.0018 0.01 Some evidence of delayed Cooper & Jacob 3120** 0.000073 yield as the rate of Gilbert St 12.1 H3 Gilbert St drawdown changed during Theis 3120 0.000073 the time period. AVERAGE 2430 0.00065 *Cooper & Jacob analysis is affected by the early time data. When this is removed from the analysis, T = 4290 m2/d and S = 0.23. These are close to the Theis transmissivity and storativity.
**Using late time data only for Cooper & Jacob analysis of Gilbert St, a transmissivity of 1760 m2/d and a storativity of 0.012 are derived
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Table 4-4 Calculated early time values of transmissivity and storativity for the Candover abstractions
Beta (for Abstraction Pump rate Observation Transmissivity Storativity (-) Type curve Neuman Evidence of delayed yield? borehole (Ml/d) borehole (m2/d) (to 2 s.f) analysis) Theis 2420 0.035 Some – Rate of drawdown Axford 1A & 7.1 OB1 Axford Cooper & Jacob 2990 0.019 reduces part way through 1B analysis period AVERAGE 2705* 0.027
Neuman (Early data) 2600 0.020 0.01 Not visible in the period of data used for analysis, but Bradley 2A Theis (Early data) 3140 0.023 10.3 OB2 Bradley delayed yield may have & 2B Cooper & Jacob 3560 0.017 occurred later, after the intensive monitoring period AVERAGE 3100 0.02
Theis 1880 0.020 Not visible in the period of Cooper & Jacob data that can be seen, but Wield 3A & OB3 Preston 2250 0.014 7.7 (Late data) delayed yield may have 3B Drove Neuman (Late data) 1710 0.022 0.001 occurred later after the intensive monitoring finished AVERAGE 1950 0.017 *Transmissivity and Storativity derived from the Axford 2011 pumping test are lower than previously seen at this location. The cause for this is currently unknown, but may be related to the joint testing of the boreholes or the lower antecedent groundwater levels and therefore these results should be used with caution.
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4.3.2. Aquifer properties – comparison with 1976 and 1989 The aquifer properties derived from the early time pump testing (Section 4.3.1) have been compared with those derived from the previous pump testing. Two significant periods of pump testing have been carried out in the past on the Candover and Alre schemes: in 1975 and 1976 on the Candover Scheme and 1989 on the Alre scheme. To facilitate a comparison of the test pumping results, the antecedent hydrological conditions for the three significant pumping tests have been compared.
Figure 4.4 shows regional pre-pumping groundwater levels from the 1975/1976, 1989 and 2011 tests. Although the three sets of groundwater levels are pre-pumping, they are from different points in the hydrological year, and differing lengths of time before the start of pumping. The dates are shown in Error! Reference source not found..
Table 4-5 Pre-pumping groundwater levels for 1976, 1989 and 2011 tests
Test Scheme tested Test pumping period Pre-pumping groundwater level dates 1976 Pumping test Candover May – November 1976 March 1975 1989 Pumping test Alre May 1989 – February 1990 May 1989 2011 Pumping test Candover & Alre September 2011 – January 2012 September 2011
Generally, 2011 pre-pumping groundwater levels are lower than those shown for the 1976 and 1989 tests. This is probably because they are from later in the summer recession (September, compared with March and May), but also because the pre-1976 levels (from March 1975) are a year in advance of the critical 1976 drought. The groundwater flow in the Upper Itchen is driven by the groundwater mounds on the catchment boundaries. It can be seen in Figure 4.4 that the Medstead and Ellisfield mounds are lower in 2011 than on the other two dates and also the groundwater gradient is shallower in 2011. The Medstead Mound is also located slightly further north and west in 2011 than on the other dates.
In the Candover catchment, groundwater levels on the three dates are more similar than in the Alre catchment. Some groundwater levels in the Candover catchment (e.g. north of the perennial head of the stream) are identical in 1975, 1989 and 2011. There are larger variations in level in the Alre catchment.
Although absolute groundwater levels vary between the contour dates, the flow directions are very similar on all three dates.
Alre aquifer properties The Alre abstractions were initially tested in 1984, soon after installation, and then at the start of the full operational test of 1989. Transmissivity (T) and storativity (S) were derived for all four boreholes on both occasions. These results and those derived from the pump testing of the current investigation are shown in Table 4-6. The 1984 testing was carried out at lower rest water levels than the 1989 testing (Southern Science, 1991). In addition to this, some additional well development is likely to have occurred during the 1984 testing which will have impacted the 1989 aquifer properties.
The differences in hydrological conditions between the 2011 testing period and the 1989 testing period will have had an impact on the aquifer properties derived. In particular the lower groundwater levels in 2011 are likely to have had an effect on storativity, as it has been previously suggested that higher groundwater levels lead to higher storativity in the Alre and Candover catchments (Southern Science, 1991; Southern Water Authority, 1979). The differing groundwater levels can also affect transmissivity, as in lower groundwater conditions, some Chalk flow horizons can be dewatered. In addition the Gilbert Street borehole used for the 2011 testing has been drilled since the 1989 testing due to the poor performance at that time. There may be an element of well development at this site as a very slight milkiness was reported for a short time in the discharge water at the outfall (pers comm. A. Matthews EA)
On the whole, the 2011 transmissivities at the Alre boreholes are similar to those previously seen, although some boreholes are slightly lower. This may be related to the lower rest water levels in 2011. Storativity was lower in all the boreholes in 2011 except West End Vale, and it is considered that this is due to the lower initial groundwater levels, in line with previous reporting (see above).
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It should be noted that the testing in 2011 was not as intensive as the 1984 or 1989 testing. Monitoring data cover a shorter time period and there are generally less frequent data at very early times. This may also have had an effect on the aquifer properties analysis and therefore the transmissivities and storativities derived.
West End Vale – The transmissivity derived in 2011 is within the range of previous results (3979 to 5619 m2/d) although it is in the lower portion of this range. The 2011 storativity was slightly higher than that previously found.
Soames Farm – The 2011 transmissivity, although within the range previously recorded, is an order of magnitude lower than the previous maximum transmissivity (12,231 m2/d) and substantially lower than the average of the previous testing results (8,501.5 m2/d). Storativity was similar to that found in 1984, but higher than that found in 1989. This is contrary to what would be expected as 1984 and 2011 had lower groundwater levels. However, as noted in Table 4-3 the early time data has an influence on the results and later time data produces values much closer to those calculated from 1984 testing.
Ropley Soke – Both transmissivity and storativity derived from the 2011 testing are lower than those previously derived in 1984 and 1989, although they are of the same order of magnitude as previously seen.
Gilbert Street – 2011 transmissivity is lower than the 1984 and 1989 results, although of the same order of magnitude. Storativity derived in 2011 is at least one order of magnitude lower than the previous results. However, it should be noted that a new borehole and pump have been installed at Gilbert Street since the 1984 and 1989 testing. It is thought that no extended testing of the new borehole has occurred since its installation, and some development of the well may have been occurring during the 2011 testing which would not be reflected in these transmissivity and storativity values. The very slight, short duration white milkiness observed in the outflow by the EA (described above) provides supporting evidence for this process. Again, as noted in Table 4-3, use of later time data from 2011 produces parameter values much closer to those from 1989.
Table 4-6 Alre borehole aquifer properties: comparison with previous test results
2011 Pump testing 1984 Pump testing 1989 Pump testing Abstraction Observation (Average result) borehole borehole T (m2/d) S (-) T (m2/d) S (-) T (m2/d) S (-) West End F4, 1 Bighton 5124 0.00249 5619 0.0043 4735 0.013 Vale Rd 3979 0.00524 5519 0.005 7320 0.2118 12231 0.0039 Soames Fm Soames Place 5870 0.21 4844 0.2699 9611 0.0057 G3A Ropley 5409 0.1188 8053 0.023 Ropley Soke 5317.5 0.013 Soke 7840 0.0408 7779 0.026 3088 0.00496 2843 0.012 H3 Gilbert Gilbert Street 3581 0.00354 3558 0.0088 2430 0.00065 Street 3606 0.009
Candover aquifer properties The Candover abstraction boreholes were drilled between October 1974 and April 1975. Following installation, they were then tested between May and October 1975. The tests were carried out on boreholes individually and in pairs, and were aimed at obtaining yield/drawdown characteristics as well as determining aquifer properties. Both step-tests and aquifer tests were carried out. In 1976, all six boreholes were pumped from May to November in a long-term test of the scheme. Data collected at the start of this test were also used to derive aquifer properties. These results and those derived from the pump testing of the current investigation are shown in Table 4-7 alongside the average results of the 2011 testing. It should be noted that although comparisons have been made with the previous results, the testing regime in 2011 was different to that of the 1975/1976 testing.
As discussed for the Alre boreholes aquifer properties, the prevailing hydrological conditions in 2011 and in 1975/1976 will have impacted the derived aquifer properties. The available regional groundwater levels prior
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Overall, the 2011 transmissivities at the Candover boreholes are lower than those recorded in 1975 and 1976. This may be related to the lower rest water levels in 2011, but may also be influenced by the 2011 testing being joint well testing, and not for individual boreholes. Storativity is similarly lower in the 2011 testing, with values recorded being at least an order of magnitude lower than seen in 1975/76. This is consistent with the trend expected that lower rest groundwater levels are associated with lower storativity (Southern Science, 1991; Southern Water Authority, 1979). As for the Alre testing in 2011, the testing of the Candover scheme was not as intensive as that carried out in 1975 or 1976.
Axford – The transmissivity derived in 2011 is lower than that previously seen. It is considered that this may be the result of the joint testing of the boreholes (1B has historically been known to have poorer properties) and may also be affected by the lower rest groundwater levels.
Bradley – The 2011 transmissivity is lower than previously derived at Bradley, although it is close to the lowest previous value. The storativity here is lower than previously found.
Wield – As at Bradley, the 2011 transmissivity is lower than previously derived at Wield, although it is close to the lowest previous value. The storativity is also lower than previously derived.
The values observed for the Candover boreholes are within the range expected for the Chalk.
Table 4-7 Candover borehole aquifer properties: comparison with previous test results
Location Observation Abstraction 1975 Pump testing 1976 Pump testing 2011 Pump testing borehole borehole (Average result) T (m2/d) S (%) T (m2/d) S (%) T (m2/d) S (-) 3300 2.6 3400 2.4 1A Axford OB1 Axford 3100 2.6 1A + 1B 2705 0.027 2A 5100 1.1 11300 0.8 Bradley OB2 Bradley 2B 3900 1.2 2A + 2B 5000 1.4 3100 0.02 3A 5100 1.1 6100 1.2 OB3 Preston 5000 1.1 Wield 3B Drove 5300 0.8 3A + 3B 1950 0.017 Note – in 1975 no analysis carried out from OB1 Axford on 1B and no analysis carried out from OB2 Bradley on 2B; in 1976 no analysis carried out from OB1 Axford on 1B and no analysis carried out from OB3 Preston Drove on 3B.
Overall the pump testing undertaken in 2011 provides a general agreement with values obtained during previous tests. Differences in values reflect the difficulty of obtaining aquifer parameters as well as differences between test length and antecedent conditions. This is especially true in fractured Chalk which often does not fit especially well with the isotropic homogeneous model on which the equations used to calculate aquifer parameter values are based. There is also a suggestion in previous reports (Southern Science 1990) that non-laminar flow may occur due to the semi-karstic / high transmissivity nature of the chalk in this area and this may also limit some of the assumptions for the analysis. Furthermore, the pumping tests were undertaken over a much shorter time frame than would usually be adopted for a pumping test to determine aquifer parameters and this was necessarily a pragmatic decision as the main emphasis in the time available was on the net gain of the scheme. In conclusion, while it is useful to calculate aquifer parameters the values derived from these short tests in 2011 should be considered as a high level guide and only used with caution to inform decisions in for example groundwater modelling or other studies.
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4.4.1. Regional drawdown Groundwater levels throughout the Upper Itchen catchment were measured immediately prior to the start of pumping and throughout the test using a combination of continuous monitoring devices and manual measurements (see Section 3.4.1). These data have been used to draw contours of groundwater levels at several times during the test period using SURFER 8.05:
Before pumping began - 6th September 2011 (Figure 4.4); All the pumps had been switched on - 29th September 2011 (Figure 4.5); 21 days pumping from all abstraction boreholes - 14th October 2011 (Figure 4.6); and Before shutdown commenced: 28 days pumping - 25th October 2011 (Figure 4.7.
The cone of depression resulting from 28 days pumping from the Candover and Alre schemes can be seen in Figure 4.8. This shows the maximum drawdown for the pumping test. The 0.1 m drawdown contour has been used to mark the outer extent of the cone of depression.
The pattern of the cone of depression largely conforms to the pattern expected from previous testing; drawdown is greatest closest to the abstractions: one area around the Candover boreholes (3.5 m drawdown) and one around the Alre boreholes (4.5 m drawdown). The cone of depression extends as far North as Ellisfield, and as far West as the Candover Stream and the Cheriton Stream. To the east, the boundary of the cone of depression is less defined, but in the Candover area, it does not appear to extend as far as Alton and in the Alre area, but extends as far as Farringdon. To the south, the cone of depression extends further away from the abstraction boreholes. It extends into the Meon catchment, showing that the interfluve between the Cheriton and the Meon was not a barrier to groundwater flow. Overall, the southern part of the cone of depression (from Alre abstraction) extends farther from the abstractions than the northern Candover part.
There are two areas where the general pattern of the cone of depression is reversed compared to previous data. One of these is the area between the Alre and Candover abstraction boreholes, around Medstead, where an area of lower transmissivity is known to affect the groundwater levels causing the Medstead Mound. The other is an area to the south-east of the Alre abstraction boreholes in the vicinity of Froxfield. This is also known to be a regional high in groundwater levels and lies on the boundary of the Upper Chalk.
Comparison of Figures 4.4 to 4.8 shows the development of the cone of depression throughout the pumping test. From this, it is observed that the cone of depression around the Alre abstractions extends outwards very rapidly. On 29th September (Figure 4.5), after just six days of maximum abstraction, the furthest extent of the cone of depression in the Alre area reaches almost to the same extent as can be seen just before shutdown began (Figure 4.8). Even though the Alre pumps were switched on earlier than the Candover ones (Section 4.1), it is still considered rapid development of the cone of depression. This contrasts with the Candover area where a steady growth in the areal extent of the cone of depression can be seen during the pumping test.
The cone of depression at maximum drawdown for the 2011 test pumping (24th October 2011) has been compared to the cones of depression derived in the 1976 and 1989 test pumping (Figure 4.8). In order to make a fair comparison, both cones of depression after 30 days pumping have been used (not the maximum drawdown) as these tests were longer duration than the 2011 test.
As previously discussed, the 1976 test only included the Candover scheme. The 1989 test primarily focussed on the Alre scheme, although the Candover scheme had to be used later on in the test (approx. 90 days after the pump test started). Therefore the comparison with the 2011 test, where both schemes were used, must take these differences into account.
Candover area – comparison with the 1976 cone of depression The extent of the cone of depression around the Candover abstractions in 2011 is very similar to that seen in 1976. The northern, eastern and western boundaries of the 2011 cone of depression lie very close to those of the 1976 cone. To the south of the Candover abstractions, the 2011 cone of depression is influenced by the Alre abstractions and the cone of depression extends further south than seen in 1976. The maximum drawdown seen in 2011 in the Candover area is 3.5 m, which is slightly greater than that seen in 1976 after 30 days of pumping.
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Alre area – comparison with the 1989 cone of depression Comparison of the 2011 cone of depression round the Alre abstractions and the 1989 cone of depression shows them to be of generally similar shape and extent. However, when looked at in more detail, there are some differences, the most significant of which is the location of the centre of the cone of depression. In 1989, this is located around West End Vale and Ropley Soke, which is further north than has been found in 2011 (when it was centred on Ropley Soke and Gilbert St). This may be in part related to the problems encountered at Gilbert Street in the 1989 test which limited the abstraction from here. However, the reduced drawdown at West End Vale suggests that different aquifer properties have been encountered in 2011 compared to those in 1989 at this location. This is most likely due to the lower groundwater levels for the September 2011 test compared to those at the time of the 1989 testing. Another difference which can be seen when the two cones of depression are compared is that the groundwater gradient between the Alre abstractions and the Medstead Mound is much steeper in 1989 than in 2011.
The furthest extent of the Alre cone of depression in 2011 and 1989 is similar to the south and the west of the abstractions. However, in 2011 the drawdown extends further down the River Alre than was seen after 30 days pumping in 1989. The Alre cone of depression in 1989 extends north into the Candover area, as far as Axford and Moundsmere Manor, even though abstraction was not occurring from the Candover scheme at this time.
It is difficult to compare this with the northern extent in 2011 as abstraction occurred from the Candover scheme, but as some drawdown is seen between the two areas of abstraction (around Heath Green and Godsfield Farm) in 2011, it may be that this is due, at least in part, to the Alre abstractions. The maximum drawdown seen in the 2011 test is very similar to that seen in 1989 after 30 days pumping (4 m).
Adjacent catchments – comparison with previous testing Before comparing results from 2011 with those from 1989 it is necessary to review the relative density and locations of monitoring points for the two tests. This has been done by dividing the region up into areas bordering the adjacent catchments and an assessment of the number of monitoring locations made in order to provide some context for the comparison.
Area south of Cheriton / Soames Farm ABH bordering the Meon catchment
A similar number of sites (20-25) were monitored during the 2011 and 1989 testing in this area, however in 2011 there were slightly more located due south of the Cheriton and slightly fewer located directly south of Soames Farm and the Meon compared to 1989. The frequency of monitoring was good in 2011 for this area as there were four sites with continuous monitoring devices installed, however for assessment of impact for longer periods of pumping, this is not directly relevant.
Area west of Candover scheme abstraction boreholes towards Dever catchment
A similar number of sites were monitored during both 2011 and 1989 tests with slightly more in 2011 to allow additional focus on the impact on groundwater levels between the Candover stream and River Dever.
Area east of augmentation abstraction boreholes
To the east of the Candover augmentation abstraction boreholes there are slightly fewer observation boreholes in 2011 compared to 1989 and this is also the case to the north east of the Alre abstraction boreholes in the vicinity of the Medstead Mound, but it is the difference between three boreholes being used to control the contours in the area in 1989 vs two in 2011.
Overall the number and spatial distribution of sites on which to base groundwater contours were very similar and provide the same degree of control on contouring in both 2011 and 1989.
During the 1989 test pumping, after 30 days pumping, the cone of depression had spread north into the Candover catchment, as well as in a “narrow ‘v’ shape towards the River Meon” (Southern Science, 1991) into the Meon catchment and to the Cheriton catchment to the south. No impact was seen to the east of the abstractions in the Wey catchment, or beyond the Candover to the Dever catchment at this stage in the test. Similar impacts were seen on the adjacent catchments in the 2011 test pumping. No impact was seen in the Wey or Dever catchments, and the main impact was found in the Alre and Candover catchments. As previously discussed, the impact in the Candover catchment was greater than in 1989 as the Candover scheme was also pumped in the 2011 test, unlike in 1989. The “v-shaped” extension to the south of the Alre abstractions into the Meon catchment was seen again in 2011, but extended further south, reaching as far as the River Meon. This may have depleted flows in the River Meon due to the reduced groundwater gradient to
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Itchen Implementation NEP Scheme the stream, however as the river would have been perched at this time the magnitude of this impact is unlikely to be significant . Similarly, the cone of depression extended further into the Cheriton catchment in 2011 than was seen in 1989, although it had minimal impact on the Cheriton Stream itself. During the 1976 testing, after 30 days the cone of depression only affected the Candover catchment, with no impact on surrounding catchments. The Candover area of the 2011 cone of depression does also not extend into the adjacent catchments.
4.4.2. Groundwater level time series Groundwater levels measured at the observation boreholes closest to the abstraction sites are shown in Figures 4.9 (Candover) and 4.10 (Alre).
In the Candover area, the three observation boreholes closest to the abstraction sites are within 400 m of the abstraction sites. At all three, a response to the start of pumping is seen within hours. At Axford (the last Candover boreholes to be switched on) a drawdown response to the pumping at Bradley and Wield can also be seen before Axford is started. The maximum recorded drawdowns are given in Table 4-8. The maximum drawdown is similar at all three sites, between 2.21 and 2.62 m. The recovery response can be seen at all three observation boreholes. However, at Axford, the effect of the reduced abstraction which was carried out, rather than a full shut down, can be seen in the smoother change in groundwater level.
In the Alre area, the four abstraction boreholes also each have one observation borehole nearby. At Ropley Soke, Gilbert Street and West End Vale, they are within 50 m of the abstraction. At Soames Farm, it is within 200 m of the abstraction. Where continuous monitoring data are available at pump start-up, it can be seen that there is a rapid response to the start of pumping at each location, within hours. The maximum drawdown is more varied here, (see Table 4-8) between 1.21 and 9.41 m and there is not a consistent relationship between radial distance and drawdown. It is particularly noticeable that at West End Vale, the maximum drawdown is only 1.21 m, although the observation borehole is 11 m distant. The recovery response to the abstraction shut down is very clear and rapid at Ropley Soke and West End Vale. At Gilbert Street, there is an initial recovery response when West End Vale and Ropley Soke were shut down and a second one when the Gilbert Street abstraction was reduced. At Soames Place, the borehole went dry and so the recovery response cannot be clearly seen. Furthermore, Soames Farm, the nearest abstraction to Soames Place, failed early on in the test and was therefore not running at the end of the test.
Table 4-8 Maximum drawdown recorded at observation boreholes close to abstraction sites during the test pumping
Observation borehole Radial distance to nearest Maximum drawdown (m) augmentation scheme (Calculated from a baseline on abstraction borehole (m) 6th September 2011) OB1 Axford (Axford) 225 2.21 OB2 Bradley (Bradley) 349 2.52 OB3 Preston Drove (Wield) 162 2.62 Ropley Soke G3A (Ropley Soke) 41 4.21 Soames Place (Soames Farm) 168 2.15 F4, 1 Bighton Rd (West End Vale) 11 1.21 H3 Gilbert Street (Gilbert Street) 5 9.41
In the wider Upper Itchen catchment, there is a varied response to the abstractions as would be expected. The maximum drawdown at each observation borehole used in the investigation (excluding those shown in Table 4-8) can be seen in Table 4-9. The patterns described here echo those shown by the regional contour plots discussed above. The observation borehole locations can be seen in Figure 3.5.
The data in Table 4-9 show that there does not appear to be a direct relationship between distance from abstraction and drawdown. Instead, it appears that drawdown is controlled by local heterogeneities in geology and transmissivity. The largest drawdowns (> 2.5 m) are seen in the Alre area between Ropley Soke and Gilbert Street boreholes and Bishops Sutton (e.g. Ropley Dean and Ranscombe Farm). This is along the Alre dry river valley. There is also an area of medium response (4 – 1.5 m) around the Candover boreholes, particularly Preston Candover and north of Axford (Nutley). In the Alre area, surrounding the largest drawdowns a medium-sized response can be seen (e.g. H4 Brislands Lane, Bighton Crossroads and I3 Abbotscroft Farm).
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In general, no response is seen in boreholes to the west of the Candover Stream from North Waltham in the north to Northington Down Farm further south. The other extents of the response to the abstraction were discussed in relation to the regional groundwater levels above. The Medstead Mound and an area near Froxfield are clearly visible as areas with zero or minimal drawdown in response to the abstractions. This is consistent with observations earlier in this section.
Table 4-9 Maximum drawdown recorded at observation boreholes during the test pumping
Observation borehole Radial distance to nearest Maximum drawdown (m) augmentation scheme (Calculated from a baseline on 6th abstraction borehole (m) September 2011) Wield OBH 6 4.05 G2 Railway 355 4.11 H4 Brislands Lane 540 3.59 I3 Abbotscroft Farm 554 2.46 Breach Farm Cottages 950 1.85 Heath Green, FIRAS 3 1076 0.56 OB10 Nutley 1505 1.68 Moundsmere Manor 1536 2.01 OB4 Preston Drove 1590 2.00 Four Marks, FIRAS 27 1641 0.08 OB7 Chilton Candover 1715 1.22 Lyeways, FIRAS 18, Ropley 1764 0.91 Hook Cottages 1843 4.76 Ranscombe Farm, FIRAS 25 1947 3.03 Trinity Hill, FIRAS 2317 None Hawthorn, FIRAS 19 2487 0.16 Ropley Dean 2493 2.49 OB9 Bugmore Hill 2494 0.93 Kitwood Plantation 2577 1.87 Long Houses, Bramdean 2659 0.44 Breach Farm New 2665 1.29 Newholme Ellisfield (“September”, 2700 0.50 College Lane) New Copse, FIRAS 15 2860 0.14 Bighton Crossroad, FIRAS 26 2930 1.79 Parsonage Farm, Bramdean 3427 1.14 Holt End, FIRAS 30A 3661 0.27 Bailey Green, FIRAS 12 3738 1.08 OB8 Brown Candover 3977 0.04 Cheriton Wood 4076 1.30 Lone Barn, B Candover 4117 0.00 West Meon A32 4252 1.15 Farringdon Station 4340 1.54 Hurst Farm, Herriard 4447 0.21 Bishops Sutton Cress beds, FIRAS 4460 3.65 23 OB13 Foxhill 4500 0.00 OB12 Lanham Lane 4502 1.04 Manor Fm, Woodmancott 4593 None
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Observation borehole Radial distance to nearest Maximum drawdown (m) augmentation scheme (Calculated from a baseline on 6th abstraction borehole (m) September 2011) Ellisfield 4641 None Pelham Place 5102 1.51 Little London, Hazeldene, 5489 0.40 Bramdean Walnut Cottage, N. Waltham 5714 None No 85 Swarraton (Holly Cottage) 5821 0.03 Marldell 6076 0.38 Waterwheel, Northington 6411 0.01 Slade Farm, FIRAS 14 6525 None Westbury House 6894 0.65 Northington Down Fm 6917 None Cocksford Little Chef 7054 None Brocklands Farm, West Meon 7324 0.36 East Stratton P O 7346 None Selborne 7386 1.99 Drayton 7645 0.89 Weststratton, Micheldever 7664 None Cheriton Tennis Court 7700 0.10 Abbotstone Down 7760 0.48 Alre Gardens, Alresford 7873 0.11
The groundwater level timeseries for those locations where continuous groundwater level monitoring was carried out are shown in Figures 4.11 and 4.12 for the Candover and Alre areas respectively. It can be seen from these graphs that a steady state was not achieved, and when shutdown began on 25th October, groundwater levels at all affected locations were still declining. It can also be seen from these graphs that whilst the maximum drawdown is not directly related to distance from abstraction, the speed with which a response is seen at an observation borehole after abstraction starts does appear to be related to the radial distance from the abstraction. Although, consistent with the observations from the drawdown contours, the response in the Alre catchment appears to be more rapid than that of the Candover.
4.4.3. Bishops Sutton Cress beds The groundwater levels around the cress beds on the River Alre are of particular interest as historically, the augmentation scheme has drawn down groundwater levels to the point at which spring flow to the cress beds no longer occurs. Groundwater levels at the Bishops Sutton cress beds have been monitored continuously as they are of particular importance.
It can be seen from Figure 4.12a that after abstraction began on the Alre scheme on 13th September 2011 at West End Vale, a visible response was seen at this observation borehole within 62 hours (5 cm). An increase in rate of drawdown can be seen at the same time as total abstraction increased (16th September 2011), but it is unclear whether this is a further response from the initial pumping, or a result of the increased abstraction as other boreholes were started. The Bishops Sutton cress beds observation borehole is approximately 4.5 km from the abstraction boreholes, and a response this rapid would generally be considered unusual. Groundwater levels in the Bishops Sutton cress bed observation borehole were monitored in the 1989 test as well as in the 2011 test. During the 2011 test, maximum drawdown recorded was 1.55 m, compared with 2.8 m maximum drawdown in 1989. However, there is a difference in pumping periods between these two tests. Therefore, it has been estimated from the 1989 groundwater hydrograph for this borehole (Southern Science, 1991, Figure 31), that after 30 days pumping, a drawdown of 1.6 m was seen. The cress bed owners reported that they had to supplement flows from their springs by using water from the pipeline after 14-21 days of pumping the Alre scheme (Alison Matthews, personal communication). The reporting of the 1989 test pumping did not include the length of time after pumping started that an impact was seen at these cress beds. However, it was reported that severe depletion of groundwater flow
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Itchen Implementation NEP Scheme was seen by August (approximately 90 days pumping), and that it is likely that depletion commenced before this (Southern Science, 1991, p144).
During the 2011 test pumping, the groundwater at the cress beds responds rapidly to the shutdown at Ropley Soke and West End Vale. The recovery, however, is limited by the abstraction that is still occurring at Gilbert Street.
4.4.4. Local abstractors and other water users The Environment Agency received queries from one protected right located close to West Meon. The owner was concerned about levels in the borehole as the low level alarm kept tripping. However it is not clear that this could definitely be attributed to the abstraction as monitored groundwater levels in this area indicate a response to abstraction of 0.5 m or less at the end of the test period (see Figure 4.8). Further investigation of the borehole, depth and pump level would be required to better understand the possible impact of augmentation scheme pumping at this location but water levels in that area had naturally been at a similar level in 2005 with no problems reported then.
The operators of Bishops Sutton and Drayton cress beds noted that they believed that the spring flow at both sites had reduced.
4.5. Impact of long term pumping on river flows
4.5.1. Stream flow results Figure 4.13 shows the stream flow at each of the gauging stations in the Itchen catchment during the augmentation scheme testing period. Note that the flows at Riverside Park have not been analysed as there were significant problems with the gauging station during the test pumping period introducing too high a level of uncertainty. The rainfall recorded at Bishops Sutton raingauge and total augmentation abstraction are also plotted for comparison.
On inspection of the stream flow plots, there are several immediately noticeable features. The impact of the augmentation on river flows is visible at Borough Bridge (Candover Stream), Drove Lane (River Alre) and Easton (Itchen) gauging stations as an increase in flow during the test pumping period. This response is less clear at Allbrook & Highbridge (Itchen) and cannot be seen at Sewards Bridge on the Cheriton Stream. The stream flows at all of the gauging stations show a response to the rainfall events before and after the test pumping period (18th August, 24th August, 4th September and 3rd November). During the test itself, minimal rainfall was recorded at Bishops Sutton, and this is reflected in the stream flows. In fact, stream flow is similar after the augmentation to that seen before at all of the gauging stations, indicating the test occurred in a relatively stable period.
4.5.2. Regression analysis of river flows In order to quantify how stream flows were affected by the Candover and Alre pumping tests, it was necessary to estimate what the natural flows of the streams would have been during the pumping period. The methodology used follows that employed by the Southern Water Authority in 1979 as part of the Candover Pilot Scheme, which is outlined in the final report for the Scheme (Southern Water Authority, 1979). This enables direct comparison of the results for the latest pumping test with those obtained from the 1979 study.
4.5.2.1. Methodology for calculating the effects of pumping on stream flows In keeping with the 1979 methodology, the term net gain is used to refer to the amount by which natural stream flows are increased by the pumped discharge, Figure 4.15. Net gains can only be computed for the River Itchen, River Alre and Candover Stream by estimating the natural stream flows and determining the difference between estimated natural flows and observed flows. This was achieved by comparing historical flows of the River Itchen, River Alre and Candover Stream to those of the Cheriton Stream at Sewards Bridge, which should not be affected by the pumping tests.
Justification for using Sewards Bridge gauge
When the Alre scheme was tested in 1989 the analysis of the net gain used the Fullerton gauge on the River Test as the Cheriton Stream was impacted by abstraction from the augmentation scheme. Due to the shorter duration of the 2011 test it was considered unlikely that the Cheriton stream would be impacted, however, an
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Itchen Implementation NEP Scheme assessment of the extent of the cone of depression created by the Alre abstraction was made and a review of the percentage depletion estimated for the Cheriton stream from the 1989 testing was undertaken.
Extent of cone of depression
Five groundwater levels were assessed for boreholes located between the Alre augmentation scheme sites and the Cheriton Stream, the locations are shown in Figure 4.15a and distances to the nearest abstraction point given in Table 4-10
Table 4-10 Observation borehole distance to nearest abstraction
Site name Distance to abstraction (m)
Cheriton Wood 4077
Kilmeston Roadside 8502
Cheriton TBC, SOURCE 7202
Parsonage Farm, BRAMD 3442
Little London, BRAMDE 5492
The groundwater level recession curve prior to the start of the test was assessed for each borehole and extended through the test period to establish the drawdown, if any, that might be attributable to the augmentation scheme abstraction. The dashed black lines on the graphs in Figure 4.15a indicate the extrapolated recessions for each of the boreholes. In the boreholes closest to the Alre scheme Parsonage Farm and Cheriton Wood appear to have an additional drawdown above that expected of 0.4 and 0.65m respectively after approximately 40-50 days of pumping. The boreholes closer to the Cheriton Stream, Little London and Kilmestone Roadside show a similar but smaller response and the borehole closest to the stream, Cheriton Source, shows a rise in groundwater levels. This is probably due to rainfall from prior to the test start.
It is concluded that although the 2011 testing had an impact on groundwater levels in the Cheriton catchment this was not observed in boreholes closest to the stream and is therefore likely to have had an insignificant impact on the Cheriton Stream flows.
1989 Report on Alre testing
Previous analysis of the Alre test pumping in 1989 (Southern Science 1990) used the flow gauge at Fullerton to develop a regression analysis. This was identified as the only chalk catchment in Hampshire unaffected by the 1989 pumping test. It also has a similar flow range to Drove Lane, Sewards Bridge and Borough Bridge.
The report states that:
The sites with particularly low coefficients of determination were Drove Lane (R2=0.46), Allbrook and Highbridge (R2=0.37) and Borough Bridge (R2=0.61). Some doubt must therefore be cast on the validity of the flow predictions derived using these regression models, but with these exceptions the values of R2 derived from the regression analysis of the river flow recessions suggest that reasonable flow predictions should be possible.
Using a water balance approach, the 1989 Alre testing found that there was evidence to suggest that there was a gradual increase in depletion with time, but concludes that it may not have been significant until the cone of depression reached the Cheriton Stream around two months after the start of pumping. The estimate of the volume of flow depletion in all peripheral streams (Candover, Cheriton, Dever, etc) is 9Ml or 1% after 30 days rising to 782Ml or 20% after 90 days. Given that the 2011 test lasted approx 40 days at high abstraction followed by approx. 20 days at reduced output, this suggests that impact on the Cheriton stream depletion during the initial 40 days would have been less than 1% and for the following 20 days may have been around 5%, although this is difficult to estimate.
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Summary
From the evidence available the Cheriton stream is therefore considered the most suitable from which to develop regression relationships and use for net gain analysis as:
the regression relationships with Sewards Bridge of the Cheriton Stream are much stronger than for the Fullerton gauge there is evidence in the flow record that the Test catchment behaves in a different way to the Itchen during low flow periods and after rainfall (M. Packman pers comm.) and Southern Science Report 92/6/450 (1992) analyses differences in groundwater levels between the Test and Upper Itchen catchments and concludes that differences between them are due to recharge variations between the catchments; the groundwater level impacts during the 2011 test suggest little if any influence likely to impact significantly on the Cheriton Stream flows could be observed; using the estimate of the volume of flow depletion from the 1989 Alre testing indicates a less than 1% impact on flows in the Cheriton stream for the length of test undertaken in 2011.
For the River Itchen gauging stations (Easton and Allbrook & Highbridge), the volumes of water abstracted upstream of the gauging stations were added onto the flow series. For Allbrook & Highbridge, the relevant abstractions were Otterbourne surface water, Otterbourne groundwater source, Twyford (all of which are estimated to have a 100% impact on the River Itchen throughout the year), Easton and Totford (pers comm. Norline Martin, Atkins 2012). Using the “lumpy groundwater” concept used for CAMS and referred to in Section 4.5.5 of the Isle of Wight Sustainability Study – Hydrological Modelling and Augmentation Analysis (Ref 5035386/70/DG/33, July 2008) the latter two abstractions are estimated to have a 60% impact on the River Itchen from January to April and 40% impact from May to December (pers comm. Norline Martin, Atkins 2012). Otterbourne surface and Otterbourne groundwater source abstraction data were available from Southern Water from 20th June 2002, so historical flow data from this date onwards were used for Allbrook & Highbridge gauging station. For the other abstractions, data from 1st January 2000 onwards were available, so historical flow data for Easton gauging station were used from this date. Historical flow data for Borough Bridge were available from October 1970 onwards, and data for Drove Lane were available from June 1975.
Linear regression was used to determine the relationships between historic Cheriton Stream flows and those of the River Itchen, River Alre and Candover Stream. Data for the years in which previous pumping tests or pumping for river augmentation were carried out (1976 to mid-1977, 1989, 1990, 1997, 2005 and 2006 (see Table 2-4)) and for up to six months after the tests, were not used for the regressions due to the influence of the pumping on stream flows during these periods. In 1995 and 2001 the Candover scheme was run but only 39 Ml and 63 Ml were discharged to the river. In 1996 the Alre scheme was run but only 56 Ml were discharged to the river. Given the small volumes discharged in 1995, 1996 and 2001 during the operation of the schemes it was considered that the stream flows would not have been significantly affected, so data for these years were included in the regression analysis in order to maximise the data available. Stream flows from 1st September 2011 onwards were also excluded from the regression analysis due to the latest pumping test.
4.5.2.2. Linear and log regression analysis Both linear and log regressions were undertaken for historic flows at Borough Bridge, Drove Lane, Easton and Allbrook & Highbridge against flows at Sewards Bridge on the Cheriton Stream (data available from July 1970 to August 2011). Regressions were performed using daily, 7-day and 28-day rolling mean flows and their logarithms. Table 4-11 displays the principal regression parameters generated for both the linear and log regressions. The correlation coefficient is a measure of the similarity between the two flow records, and the standard error is the standard deviation of errors of prediction of natural flows about the regression line.
As can be seen in Table 4-11, the correlation coefficients for the log regressions are consistently higher than those of the linear regressions. The correlation coefficients for the 28-day linear regressions are also consistently lower than those of the daily log regressions. These patterns contrast with those of the results presented in the 1979 Candover Pilot Scheme report (Southern Water Authority, 1979), which show the opposite trend (see Table 4-12). However, Table 4-11 also shows that there is a consistent increase in the correlation coefficient from the daily data base to the 7-day to the 28-day data base for both linear and log regressions, which is also seen in the 1979 results.
Flows in the River Itchen at Allbrook & Highbridge and at Easton gauges are the most strongly related to flows in the Cheriton Stream at Sewards Bridge. Flows in the River Alre at Drove Lane show the weakest correlation with flows in the Cheriton Stream. This is consistent with the regression results for Drove Lane
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Itchen Implementation NEP Scheme from the 1979 Candover Pilot Scheme report (Southern Water Authority, 1979), which also showed the weakest correlation with Cheriton Stream flows at Sewards Bridge of all the gauging stations used.
However, the correlation coefficients presented in Table 4-11 are consistently slightly lower than those presented in the 1979 report (see Table 4-12). This can be attributed to the longer historical flow record used in the present study, which utilised a record of up to 41 years rather than the seven year (1971-1976) record used for the 1979 report.
For example, the maximum correlation coefficient for the regression of Borough Bridge flows against Sewards Bridge flows in 1979 was 0.983, whereas the maximum for the present study is 0.963 (Table 4-11). Nevertheless, the correlation coefficients presented here are sufficiently high to enable the accurate computation of estimated natural flows with only a small level of error.
Table 4-11 Summary of principal regression parameters. The regression parameters highlighted green were those chosen to estimate natural stream flows
Linear Regression Log Regression Date base, mean flows Correlation Std. error of Correlation Std. error of 3 over period coefficient estimate (m /s) coefficient estimate [-] (R2) (R2) Candover Stream at 1 day 0.913 0.087 0.927 0.113 Borough Bridge 7 days 0.918 0.083 0.934 0.108 (October 1970 to August 2011) 28 days 0.928 0.075 0.940 0.101 River Alre at Drove 1 day 0.755 0.236 0.805 0.123 Lane (total) 7 days 0.757 0.234 0.806 0.122 (June 1975 to August 2011) 28 days 0.767 0.227 0.808 0.120 River Itchen at Easton 1 day 0.850 0.669 0.927 0.090 GS 7 days 0.857 0.649 0.932 0.086 (January 2000 to August 2011) 28 days 0.871 0.608 0.935 0.083 River Itchen at 1 day 0.941 0.514 0.954 0.069 Allbrook & Highbridge 7 days 0.948 0.480 0.959 0.064 (June 2002 to August 2011) 28 days 0.955 0.437 0.963 0.060
Table 4-12 Summary of principal regression parameters from the 1979 Candover Pilot scheme pumping tests. Only results for those gauging stations used for both the 1979 pumping tests and summer 2011 pumping tests are presented. Source: Southern Water Authority (1979)
Date base, Linear Regression Log Regression mean flows over period Correlation Std. error of Correlation Std. error of coefficient estimate (m3/s) coefficient estimate (R2) (R2) Candover Stream 1 day 0.975 0.046 0.970 0.040 at Borough Bridge 7 days 0.980 0.042 0.975 0.036 28 days 0.983 0.037 0.979 0.034 River Alre at Drove 1 day 0.899 0.175 0.907 0.047 Lane (total) 7 days 0.901 0.173 0.909 0.047 28 days 0.907 0.167 0.911 0.046
4.5.2.3. The estimation of natural flows As shown in the previous section, there is only a small difference between the regression parameters for the daily, 7-day and 28-day mean flows. Therefore, daily mean flows were used for the regression equations
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Itchen Implementation NEP Scheme employed to determine the estimated natural flows. This made maximum use of the data available because gaps in parts of the historical record meant that the 7-day and 28-day rolling means could only be calculated after an interval of seven and 28 days respectively from the end of the data gap. For gaps in the record of less than ten days the flows were extrapolated across the gap, but it was not considered reasonable to do this for the larger gaps in the records.
Log rather than linear regression equations were used to estimate the natural flow because of the higher correlation coefficients for the log regressions, enabling more accurate estimation of natural flows.
The four regression equations used to estimate natural flows at the four featured gauging stations using flows in the Cheriton Stream at Sewards Bridge are shown below.
Borough Bridge Estimate of the logarithm of Candover Stream daily flows at Borough Bridge (y), where x is the logarithm of Cheriton Stream daily flows at Sewards Bridge:
y = 0.8680x ‐ 0.1989
Drove Lane Estimate of the logarithm of River Alre daily flows at Drove Lane (y), where x is the logarithm of Cheriton Stream daily flows at Sewards Bridge:
y = 0.5277x + 0.6940
Easton Estimate of the logarithm of River Itchen daily flows at Easton (y), where x is the logarithm of Cheriton Stream daily flows at Sewards Bridge:
y = 0.6159x + 1.7557
Allbrook & Highbridge Estimate of the logarithm of River Itchen daily flows at Allbrook & Highbridge (y), where x is the logarithm of Cheriton Stream daily flows at Sewards Bridge:
y = 0.6707x + 2.1424
4.5.2.4. Errors in regression estimates Figure 4.14 shows the observed daily flows and estimated natural daily flows (from the regression analysis) for the four gauging stations on the Candover, Alre and Itchen; the derivation of the upper and lower bounds shown in the plots is discussed below. As shown by this figure, the estimated natural daily flows are relatively accurate estimates of the observed daily flows during non-pumping periods for Borough Bridge and Allbrook & Highbridge flows, but less so for the Drove Lane and Easton flows. However, for Easton and Allbrook & Highbridge, for up to four months prior to the onset of the pumping, the estimated natural flows appear consistently offset from the observed flows. The approach used to rectify this offset is discussed in the next section. In all cases the onset of the pumping tests and subsequent discharge of water into the streams is clearly visible on the flow series from a sudden increase in the observed daily flows in mid- September 2011.
The certainty associated with the estimated natural flows can be expressed using 95% confidence intervals for the long-term regression relationship. These upper and lower error bounds were computed first by calculating the percentage difference between the estimated natural flow and observed flows for each daily flow value. The standard deviation of these percentage differences was then calculated for each of the four gauging stations, excluding periods affected by pumping. The confidence intervals were subsequently determined by multiplying this standard deviation by 1.96, which is the appropriate t-value for a 95% confidence interval of a dataset with more than 30 degrees of freedom, which applies in this case. The 95% confidence intervals for the estimated natural flows were calculated to be ± 21.9%, ± 24.3%, ± 17.5% and ± 13.5% for Borough Bridge, Drove Lane, Easton and Allbrook & Highbridge respectively. The lower correlation coefficient for the Drove Lane regression is reflected in the larger confidence intervals for estimated natural flows at this gauging station.
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The upper and lower bounds of the estimated natural daily flows are shown as the maximum extent of the dark blue band and minimum extent of the light blue band respectively in Figure 4.14. These represent the natural flow range expected to occur 95% of the time. Therefore, there is a 95% chance that the natural flow would have been between the upper and lower bounds of the estimated natural flow had the pumping test not taken place.
As can be seen from this figure, for Borough Bridge, Drove Lane and Allbrook & Highbridge, the observed daily flow exceeds the upper bound of the estimated natural daily flows during the pumping period. Therefore it can be stated with 95% certainty that the net gain to three of the streams is real during this period and cannot be mistaken as regression error. For Easton this level of certainty is slightly lower, but the chance that the perceived net gain is the result of regression error rather than the pumping tests remains low.
The confidence intervals used assume that the percentage error in the estimation of the natural daily flow is not dependent on the magnitude of the flow and is therefore constant for each gauging station across the flow range. The difference in flows between the estimated natural and observed flow due to regression error is therefore assumed to increase linearly as flows increase.
This assumption was tested by examining the relationship between flow and the percentage difference between the estimated natural and observed flow. As shown by Figure 4.16, the percentage difference remains approximately constant across the entire flow range for Borough Bridge, indicating that the use of a constant percentage as the confidence interval is appropriate.
4.5.2.5. Estimated natural flow adjustment for Easton and Allbrook & Highbridge As noted above, Figure 4.14c shows that from mid-June to December 2011 (excluding the pumping test period), the estimated natural flow at Easton gauging station appears to be offset from the observed flow at Easton by a relatively constant amount. The mean difference between the estimated natural flows and observed flows from 19th June 2011 (the start of the apparent offset) to 14th September 2011 (the onset of the Alre scheme pumping) is -26.8 Ml/d. It could therefore be assumed that during the pumping period, the natural flow is likely to have been lower than shown in Figure 4.14c by approximately this amount. It is unclear what this difference could be attributed to; there is no immediately obvious explanation, such as a problem with the gauge as the data has been issued as QA checked by the EA. However, factors that may impact this catchment and not the Cheriton (which the estimated values are derived from through the regression relationship) could be abstraction activities from Easton PWS or the difference in response to rainfall due to subtle differences in catchment hydrogeological behaviour or differences in rainfall due to topographical variation. It would require a detailed analysis of the rainfall patterns, hydrogeology and abstraction for the two catchments to support a more robust identification of what could account for the variation and this is beyond the scope of the current investigation.
One approach for improving the accuracy of the estimated natural flows during the pumping period is therefore to adjust the estimated natural flows (and therefore upper and lower bound estimated flows) during the period of apparent offset (19th June 2011 to 14th December 2011) by subtracting this mean difference from the estimated natural flows. This approach was discussed with the EA in a meeting held on 22nd February 2012 as a means of addressing the apparent offset. The effect of this adjustment can be seen in Figure 4.17a, in which the estimated natural flow is now a much closer approximation of the observed flow prior to and after the pumping test period. This adjustment therefore appears to be reasonable, as it is likely that flows would have remained at this slightly lower level during autumn 2011 had there been no pumping tests due to the low level of rainfall during this period. However, in practice this adjustment makes only a very slight difference to the net gains calculated for Easton gauging station, as discussed in the next section.
The same procedure can be used to adjust the estimated natural flows for Allbrook & Highbridge. These appear to be consistently lower than the observed flows from 8th May 2011 to 14th December 2011. The mean difference between the estimated natural flows and observed natural flows from 8th May 2011 to 14th September 2011 is 21.7 Ml/d. Therefore, for the period 8th May 2011 to 14th December 2011, an adjusted estimated natural flow series (and upper and lower bound estimated flows) was generated by adding this mean difference to the estimated natural flows. The effect of this can be seen in Figure 4.17b, which shows that the adjusted estimated natural flow is now a far better approximation of the observed flow prior to and after the pumping period. This adjustment therefore also seems reasonable and the adjusted flows are used for the net gain analysis.
Although the Drove Lane estimated natural flow is also a poor approximation the observed flow after the main phase of the pumping tests, the same adjustment procedure cannot be used for Drove Lane because the large offset shown in November 2011 is not mirrored by a similar offset prior to the pumping test period. Therefore a reasonable correction factor for the estimated natural flow cannot be derived, as flows at Drove
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Lane may still have been influenced by the pumping tests during November 2011. Moreover, a weaker relationship between the observed and estimated natural flow for Drove Lane compared to the other gauging stations is expected from the lower correlation coefficients for the Drove Lane regression analyses.
4.5.3. Net gain analysis on river flows The additional water in the watercourses that is attributable to the pumping (the net gain) can be computed as the difference between the observed daily flows and the estimated natural daily flows during the pumping tests. A maximum estimate of the net gain can be calculated by subtracting the lower bound of the estimated natural flows from the observed flows, and a minimum estimate can be obtained by subtracting the upper bound of the estimated natural flows from the observed flows, as illustrated in Figure 4.15. These net gains can be computed as instantaneous (daily) values in addition to the total volumetric net gain between the start and end of pumping.
The minimum, maximum and average total volumetric net gains calculated using the estimated natural flows (adjusted flow series are used for Easton and Allbrook & Highbridge) for each gauging station are presented in Table 4-13. Table 4-14 shows the original (non-adjusted) net gains.
The instantaneous volumetric net gain can be compared to the volume of water pumped each day in order to calculate the percentage of water pumped that is gained by the Candover, Alre and Itchen, termed the instantaneous percentage net gain. The overall percentage net gain can also be estimated by dividing the total volumetric net gain by the total volume of water pumped over the pumping period. The minimum, maximum and average overall percentage net gains calculated using the estimated natural flows (adjusted flow series are used for Easton and Allbrook & Highbridge) for each gauging station are also shown in Table 4-13, with the non-adjusted results shown in Table 4-13. Some of the net gains have values less than zero, shown as zero in the table, whilst others have values exceeding 100%. These are unrealistically high and are therefore shown in red.
Examination of the relationships between the observed flow and estimated natural flow prior to and after the pumping period provides an indication of which of the net gain values is the most likely (minimum, maximum or average):
For Borough Bridge, Figure 4.14a shows that the observed flow is close to the estimated natural flow prior to and after the pumping period, and therefore the most likely overall percentage net gain is the average value of 86%. This compares well to the results obtained for the 1976 Candover Pilot Scheme pumping tests, which found that the instantaneous net gain reached 90% at the start of pumping and fell to 70% after 20 weeks, at which point the overall percentage net gain was 80% (Southern Water Authority, 1979). For Drove Lane, Figure 4.14b shows that the observed flow is close to the estimated natural flow prior to the pumping period, but approximately halfway between the estimated natural flow and the lower bound of the estimated natural flow at the end of the pumping test. Therefore the most likely value is between the average and maximum values (21% and 112%), and is likely to be closer to the average value, at approximately 50%. For Easton, Figure 4.17a shows that the observed flow is close to the adjusted estimated natural flow prior to and after the pumping period, and therefore the most likely overall percentage net gain is the average value of 83%. For the original (non-adjusted) series, Figure 4.14c shows that the observed flow is approximately halfway between the estimated natural flow and lower bound of the estimated natural flow both prior to and after the pumping tests. Therefore the most likely value using these results is halfway between the average and maximum value (~85%). The similarity between these most likely values shows that the flow adjustment makes little material difference to the final results. For Allbrook & Highbridge, Figure 4.17b shows that the observed flow is close to the adjusted estimated natural flow prior to and after the pumping period, and therefore the most likely overall percentage net gain is the average value of 78%. For the original (non-adjusted) series, Figure 4.14d shows that the observed flow is approximately halfway between the estimated natural flow and upper bound of the estimated natural flow both prior to and after the pumping tests. Therefore the most likely value using these results is halfway between the average and minimum value (~76%). The similarity between these most likely values also shows that this flow adjustment makes little material difference to the final results.
The net gains are consistently high with the exception of the net gain at Drove Lane. However, the correlation coefficient of the regression equation for Drove Lane is significantly lower than that of the other three gauging stations (see Table 4-11) meaning there is a greater degree of uncertainty associated with the Drove Lane net gain results.
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The instantaneous net gain at all four gauging stations are shown in Figure 4.18. In this figure, the average instantaneous volumetric net gain and the average instantaneous percentage net gain (as a percentage of abstraction) are shown throughout the pumping period. The relevant abstraction is also shown for these locations (Candover abstraction for Borough Bridge, Alre abstraction for Drove Lane and total abstraction for both Easton and Allbrook & Highbridge gauging stations). Note that Easton and Allbrook & Highbridge use the adjusted flow series.
In general, the instantaneous volumetric net gain in flow closely follows the daily abstraction volumes. For Drove Lane, it is clear from Figure 4.18 that the average net gain is likely to be an underestimate and that the true value is likely to lie between the average and maximum values. For Borough Bridge, Easton and Allbrook & Highbridge the average net gains are the most likely estimates.
A large percentage net gain is seen at Allbrook & Highbridge around 7th November 2011. This can be attributed to a significant rainfall event around 3rd November (see Figure 4.13). The effect of this rainfall can also be seen in the flows at Borough Bridge, Drove Lane and Easton (Figure 4.13). However, the impact of the event on the net gains at these gauging stations cannot be seen as the flow increases from the rainfall event are proportionate to the increase in flows seen in the Cheriton Stream. The regression analysis carried out therefore reduces the impact of the rainfall event on the resulting net gain.
For all the gauging stations except Drove Lane, there is a peak in the instantaneous percentage net gain at the end of October. This can be attributed to the sharp reduction in pumping on both schemes at this time, whilst river levels remained high from the previously discharged augmentation water.
The instantaneous volumetric net gain itself drops off rapidly at the end of the main period of pumping for the four gauging stations. For Borough Bridge, Easton and Allbrook & Highbridge, where the pumping rate is constant (which occurred for a period of approximately three weeks) the instantaneous percentage net gain also remains stable. This contrasts with the results from the Candover Pilot Scheme pumping tests, which found a decline in the instantaneous percentage net gain for Borough Bridge from 90% at the start of pumping to 70% after 20 weeks. After 21 weeks there was a sharp fall in net gain to 25%, despite continued pumping at the full rate (Southern Water Authority, 1979). This was attributed to suppression of the recovery of flows of the Candover following the onset of winter recharge (compared to the Cheriton) as a result of stream depletion due to the pumping. However, the summer 2011 pumping tests were conducted for a duration of approximately 10 weeks, compared to around 34 weeks for the 1976 Candover scheme tests, which is likely to have been of insufficient duration for the effects of stream depletion to be visible in the results.
Table 4-13 The total volumetric net gain at each gauging station for the pumping period.Note – Easton and Allbrook & Highbridge net gains are based on adjusted estimated natural flows. Where the net gain is less than zero, these are shown as <0, and where they exceed 100% the figures are shown in red.
Borough Bridge Drove Lane Easton (14th Sept Allbrook & (19th Sept – 7th th th – 7th Dec 2011) Highbridge (14th (14 Sept – 30 th Dec 2011) Nov 2011) Sept – 7 Dec 2011) Minimum total volumetric 5.5 < 0 < 0 < 0 net gain over pumping period (Ml) Minimum overall 43.3% < 0 < 0 < 0 percentage net gain Average total volumetric 16.3 4.3 27.6 26.1 net gain over pumping period (Ml) Average overall 86.4% 20.6% 82.6% 78.1% percentage net gain Maximum total 16.3 23.3 76.2 74.8 volumetric net gain over pumping period (Ml) Maximum overall 129.6% 112.1% 228.2% 224.0%
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percentage net gain
Overall Net Gain 86% (Average ~50% (Between 83% (Average 78% (Average (Most likely estimate) value) average & max value) value) values)
Table 4-14 The total volumetric net gain at each gauging station for the pumping period. Note: The values shown for Easton and Allbrook & Highbridge use the original (non-adjusted) estimated natural flows. Where the net gain is less than zero, these are shown as <0, and where they exceed 100% the figures are shown in red.
Borough Bridge Drove Lane Easton (14th Sept Allbrook & (19th Sept – 7th th th – 7th Dec 2011) Highbridge (14th (14 Sept – 30 th Dec 2011) Nov 2011) Sept – 7 Dec 2011) Minimum total volumetric net gain over pumping 5.5 < 0 < 0 1.06 period (Ml) Minimum overall 43.3% < 0 < 0 3.2% percentage net gain Average total volumetric net gain over pumping 16.3 4.3 1.2 47.4 period (Ml) Average overall 86.4% 20.6% 3.5% 142.0% percentage net gain Maximum total volumetric net gain over 16.3 23.3 55.5 93.7 pumping period (Ml) Maximum overall 129.6% 112.1% 166.2% 280.8% percentage net gain Overall Net Gain 86% (Average ~50% (Between ~85% (Between ~76% (Between (Most likely estimate) value) average & max average & max min & average values) values) values)
4.5.4. Additional flow gauging at cress beds From July until November 2011 the Environment Agency undertook an additional programme of flow gauging at the Bishops Sutton cress beds in order to gather information about flows at the site. Additional detailed gauging at the site was considered necessary as there is a complicated network of valves and pipes that were installed as mitigation of the original development of the Alre augmentation scheme. The valves and pipe network allow the cress bed operators to divert water from the augmentation scheme main pipeline into the cress beds as necessary to compensate for the reduction in flow from the springs caused by the drawdown resulting from the operation of the abstraction boreholes (Southern Science, 1991).
This potential for diversion and control managed by the cress bed operators means that it is difficult to obtain an accurate measurement of total flow entering the Alre at this location.
Gauging was undertaken at six locations as shown in Figure 4.19 (provided by the Environment Agency). During augmentation, the total of these flows is the total River Alre flow at the cress beds, including augmentation flow, as shown below.
Total cress bed output = Main outfall + Left outfall + Right outfall + Centre bypass
Downstream of outfall = Augmentation flow (minus cress beds offtake) + river (when flowing)
Road Bridge = Natural river flow, prior to any augmentation water
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Gauging took place on 18 occasions between the 12th July 2011 and 9th November 2011 at approximately weekly intervals. The results of the Bishops Sutton flow gauging are shown in Table 4-15.
Table 4-15 Bishops Sutton flow gauging results (Source: EA, November 2011)
Flow gauging date Cress bed Output Flow at Road Flow downstream of Total flow (m3/s) flow (m3/s) Bridge (m3/s) outfall (m3/s)
12/07/2011 0.074 0.033 no measurement 0.107 20/07/2011 0.094 0.032 no measurement 0.125 28/07/2011 0.098 0.023 no measurement 0.121 03/08/2011 0.100 0.017 no measurement 0.118 10/08/2011 0.066 0.015 no measurement 0.081 18/08/2011 0.101 0.011 no measurement 0.112 24/08/2011 0.079 0.010 no measurement 0.089 31/08/2011 0.082 0.011 no measurement 0.093 07/09/2011 0.080 0.009 no measurement 0.089 15/09/2011 0.078 0.014 no measurement 0.078 21/09/2011 0.066 0.001 no measurement 0.067 28/09/2011 0.074 0 0.139 0.213 05/10/2011 0.152 0 0.040 0.192 14/10/2011 0.118 0 0.040 0.158 19/10/2011 0.114 0 0.036 0.150 26/10/2011 0.107 0 0.036 0.143 01/11/2011 0.112 0 0.036 0.148 09/11/2011 0.115 0 0.034 0.149
4.6. Impact of pumping on ecology This Section summarises the impacts of operating the augmentation schemes on ecology; full details are given in Section 7 Appendix E.
As already noted in Section 3.3.3, anomalous behaviour by the crayfish was observed immediately prior to the planned start of the pumping test that necessitated a postponement to the test start. This behaviour included crayfish being visible during daytime, when they are normally nocturnal. The concern relating to this behaviour was that the crayfish had been infected with Aphanomyces astaci or ‘crayfish plague’ and any testing would further spread the disease. Samples were sent for testing but nothing was found to indicate infection so the pumping test was given approval to continue a few days later than planned.
The operation of the Candover and Alre augmentation scheme resulted in immediate and significant modification in flow rates and water levels at two locations of regional importance for the white-clawed crayfish. Drift net surveys did not identify an effect of flow regime or flow rates on levels of crayfish drift on either the Candover Stream or the River Alre. However, the number of crayfish recorded per survey during crayfish behaviour monitoring declined across the study. HIWWT considered that it is possible that there were unrecorded effects of the Upper Itchen flow augmentation schemes on white-clawed crayfish; these include an undetected increase in levels of drift during the night or increased energetic costs associated with foraging or maintaining position within the channel, particularly during the ramp-up period of operation.
Although there were a number of trends in macroinvertebrate drift with flow, there was not a conclusive relationship between flow patterns and the numbers of drifting organisms associated with either scheme, and there were no apparent trends in other target macroinvertebrate groups and no correlation between diversity and flow rate or survey day. Pre- and post augmentation samples of the benthic macroinvertebrate community at Abbotstone Causeway recorded an increase in the number of taxa following the operation of the Candover scheme. HIWWT emphasize that this result is based upon single pre- and post-augmentation sampling.
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Maximum daytime water temperatures on the Candover Stream recorded a significant reduction as flow rates increased, but there was no such correlation between water temperature and the operation of the River Alre scheme. Reduced maximum daytime water temperatures during a seasonal period when they should be at their highest could have a negative impact upon the development of juvenile crayfish, and both these findings provide evidence to support the need for the stable, slowly incremented operation of both schemes.
4.7. Candover pipeline assessment
4.7.1. Candover pipeline capacity testing While undertaking the Candover augmentation scheme pumping test, it became clear that the sum of the maximum flow rates that could be achieved at each of the boreholes (theoretical combined yield) was higher than the perceived pipeline limit. The original pipeline constructed for the 1975/1976 testing was designed to carry a yield of 27.2 Ml/d (Southern Water Authority, 1979, p39). However, this original pipeline was laid over ground, to be buried when the outcome of the testing was known. It has been assumed that the current pipeline was designed to carry the same yield, but this has not been confirmed. In addition to this, there is some anecdotal evidence that the scheme output is limited to 27 Ml/d, yet the scheme is licensed to abstract up to 36 Ml/d. During the 1975/76 testing of the Candover scheme, it was found that the theoretical yield of the six boreholes, pumped individually, would be approximately 36.5 Ml/d. However, the actual combined output in the 1976 testing was 31.2 Ml/d, and this difference was attributed to frictional losses of the pipeline (Southern Water Authority, 1979, p39). It was therefore decided to further investigate the limits, if any, of the Candover pipeline during the 2011 testing. This was also an opportunity to compare the individual borehole flow meter measurements with the measurements recorded at the outfall.
The pipeline test was carried out on 19th October 2011 jointly by Atkins and the EA, midway through the augmentation scheme pumping test. The aim was to try to discharge more than 27 Ml/d through the pipeline but remain below the daily licence limit of 36 Ml/d. Pump configurations were used where the theoretical combined yield should have been greater than 27 Ml/d, but not so high as to overload the system or exceed the licence (Table 4-16). During the pumping, readings were taken at all of the individual borehole flow meters starting at the same time and at the same intervals. This would give a detailed record of total output from the Candover scheme while different pump combinations were used as well as testing the 27.2 Ml/d threshold. The flow over the crump weir on the Major Outfall continued to be measured by an automatic monitoring device during the pipeline test.
Table 4-16 Candover pipeline test pumping pattern - 19th October 2011
Theoretical yield based Expected yield on individual borehole based on output Time Pumps Action pump duty capacity during test to (GMT) running (from Candover O&M date (Ml/d) manual) (Ml/d) 1A, 1B, 2B, 27.6 08:00 Prior to start of pipeline test 25.6 3A Wield 3A switched OFF; 1A, 1B, 2B, 23.7 09:30 28.4 3B switched ON 3B Bradley 2A switched ON 1A, 1B, 2A, 34.1 10:10 37.4* (Maximum abstraction) 2B, 3B 1B, 2A, 2B, 30.6 12:15 Axford 1A switched OFF 32.2 3B 12:40 Bradley 2B switched OFF 1B, 2A, 3B 23.2 20.2 1B, 2A, 3A, 30.6 12:55 Wield 3A switched ON 29.4 3B End of 1B, 2A, 3A, 30.6 Left as at 12:55 29.4 test 3B Even though the total theoretical yield for individual boreholes is in excess of licensed quantity, it was not expected that the licence would be exceeded due to observed output to-date
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The results of the pipeline test are shown in Figure 4.20. This shows the output recorded at the outfall as well as the combined flow meter output. It is clear from this graph that there are differences recorded between the combined flow meter output and the outfall output. The discussion in this section therefore relies on the discharge measured at the outfall rather than the flow meter measurements. These measurement differences were not only seen during the pipeline test, but also throughout the long-term test. The reasons for these differences remain unclear, but may be related to the following uncertainties:
1. The method of calculating abstraction from the flow meters at the pumping boreholes was based on a daily reading being taken manually at each flow meter. The meter reading provides the total volume that has passed through the meter, and flow rate is then calculated from the volume and the time that has passed since the previous reading (usually one day). The resulting flow rate is therefore an average over that period. This hides some of the detail of the abstraction pattern and the method was particularly vulnerable at pump start-up and shutdown, or when being changed over.
2. The accuracy of the flow meters at the abstraction boreholes is currently uncertain. The dates when the meters were installed are not known, but they have not recently been replaced, nor does any recent calibration appear to have been undertaken. They may also be affected by pipeline constraints such as backpressure from the pipeline causing inaccurate flow measurement.
3. The crump weir at the outfall is in good condition and is not overgrown by vegetation. However, an error margin of around 5% on the flow measurements would still be reasonably expected.
The graph in Figure 4.20 shows that it was not possible to discharge significantly more than 27.2 Ml/d. During the majority of the maximum abstraction period (10:10 am to 12:15 pm), the output recorded was 27.8 Ml/d. This is slightly higher than the pipeline design yield, but the difference of 2% is considered within the acceptable accuracy of the instrumentation. Furthermore, the maximum licensed yield of 36 Ml/d was not achieved. Rapid changes in water level were observed at other abstraction sites when the pumping regime was altered elsewhere, e.g. immediate water level rise observed at Axford when Wield abstraction reduced indicating pressure effects within the pipeline impact on output from sites. It is therefore considered that the Candover pipeline remains a constraint on total scheme output.
The Southern Water Authority indicated following 1976 test pumping that adopting a larger pipeline was an option to be considered if the scheme were made permanent (Southern Water Authority, 1979). It is not known whether this has been considered during the lifetime of the scheme, but it may be appropriate to consider this again at this stage given the results of the pipeline test.
4.7.2. Pipeline modelling: results and conclusions
Results The pipeline modelling shows that the pipeline runs fully pressurised for the majority of its length. However, near the final high point the hydraulic profile shows sub-atmospheric pressure under steady state conditions. Due to the absence of an air valve shown on the survey at this high point it has been assumed that a siphon could be in operation following the initial priming of the pipeline. However, the pressure falls to near full vacuum in places, which also presents the possibility of air pockets forming and free surface, sub- atmospheric flow. In this situation the benefits of the siphon are diminished. Assuming the siphon is operating ideally, this mode of operation gives the following capacity (Table 4-17):
Table 4-17 Flow rates delivered with siphon - Scenario 1
Borehole Flow (Ml/d) Flow (l/s) Axford A 3.2 37 Axford B 2.6 30 Bradley A 6.7 78 Bradley B 6.7 78 Wield A 9.2 106 Wield B 5.3 61 Totals 33.7 390
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Pipeline Survey Drawing (96:648:01) shows that air vents/valves are installed at all high points on the pipeline with the exception of the final high point. There are two explanations for this; either the survey did not locate an air valve/valve in this position, or the pipeline was intentionally designed without an air valve to take advantage of the siphon effect described above. In the case of the latter it would normally be standard practice to install a one-way air valve to prevent air entrainment, but still allow air to exit the pipe. If the design intent was to allow the pipe to drain-out following the high point, i.e. no siphon, a two-way air valve may be present.
In order to demonstrate absence of a siphon on the system capacity the model was terminated at the final high point and re-run. In this situation the pipeline is running full upstream of the high point. A check was run to ensure that the pipeline downstream of this would drain out at this new capacity with atmospheric pressure at the high point. This assumes that the installed air valve/vent would allow sufficient air into the pipeline to prevent the formation of a siphon. The new capacity and flow rates delivered under this mode of operation are given in Table 4-18.
Table 4-18 Flow rates delivered without siphon - Scenario 2
Borehole Flow (Ml/d) Flow (l/s) Axford A 2.9 34 Axford B 2.4 28 Bradley A 6.7 78 Bradley B 6.7 78 Wield A 9.1 105 Wield B 5.0 58 Totals 32.8 381
A final scenario was run to assess the effect of the air valve/vent situated between the final high point and the Major outfall. In this situation the pipeline is surcharged upstream of the air valve and running partially pressurised, partially free surface downstream. The benefit of the siphon would be maintained up to the air valve, following priming of the pipeline. The following capacities are possible (Table 4-19).
Table 4-19 Flow rates delivered with siphon up to final air valve - Scenario 3
Borehole Flow (Ml/d) Flow (l/s) Axford A 3.1 36 Axford B 2.5 29 Bradley A 6.7 78 Bradley B 6.7 78 Wield A 9.2 106 Wield B 5.2 60 Totals 33.4 387
Discussion and conclusions The modelling has identified the theoretical flow rates delivered by each borehole in the Candover Scheme system. There is some uncertainty around the operation of the final section of pipeline, but comparisons of the results reported above demonstrate that the variation of flow rates is not strongly dependant on this. It can be considered that the variation is within error bounds, given the quality of information used in the modelling.
The modelling results indicate that the system capacity is marginally greater with the aid of a siphon (scenario 1) than without. This is due to the system operating slightly to the left of the ‘full siphon’ and ‘free discharge’ system curve intercept. Hypothetically, if the cumulative pump flow increased the system would operate to the right of this intercept and the ‘free discharge’ mode of operation (scenario 2) would be advantageous.
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Given the near full-vacuum pressures predicted in scenario 1, and the supposition of these being amplified by any transient pressures from pump start/stops it is thought unlikely that the system operates with a full siphon due to the strong potential for pipe bursts. In reality it is most likely that an air valve does exist at the final high point and the system operates as predicted in scenario 2.
The modelled result of 33 Ml/d agrees quite poorly with the sum of individual borehole field test flow rates (Table 4-20) and the total measured at the outfall (27.8 Ml/d), even given the errors associated with measurement. Reasons for the poor correlation are likely to include the uncertainty surrounding the pumps installed in each borehole and hence the assumed pump performance curves, the age of the pumps (~35 years), the possibility of the Kent Helix flow meters giving uncertain readings and the possibility of leaks at various points along the main.
Table 4-20 Recorded flows during field tests
Borehole Average Flow Flow (l/s) during test (Ml/d) Axford A 2.4 27 Axford B 2.6 30 Bradley A 9.2 106 Bradley B 8.5 98 Wield A 9.4 108 Wield B 6.6 76 Totals 38.5 446 n.b. not all boreholes were in operation at the same time, see Table 4-16 for pumping configuration.
Given that the modelling results are so different to those derived through field testing it may be necessary to undertake additional investigations to better understand the Candover pipeline. Recommendations for additional work are provided in Section 5.2.
Details of the pipeline modelling input files are provided in Appendix D.
4.8. Impact of pumping on water quality
4.8.1. Water quality samples collected during testing: Summer 2011 Samples were collected for water quality analysis by the Environment Agency during the 2011 pump testing as set out in Table 4-21.
Table 4-21 Water quality sampling programme during 2011 pumping test
Site name Grid Ref Sample dates Axford 1A SU 61049 43045 27/09/2011 19/10/2011 Axford 1B SU 61055 42988 27/09/2011 20/10/2011 Bradley 2A SU 62634 41969 19/10/2011 Bradley 2B SU 62575 41957 27/09/2011 19/10/2011 Wield 3A SU 61549 40547 27/09/2011 19/10/2011 Wield 3B SU 61528 40497 19/10/2011 Candover scheme outfall SU 56806 36754 27/09/2011 Candover Stream SU 56799 36796 27/09/2011 Candover Stream at Abbotstone SU 56371 34559 19/09/2011
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22/09/2011 27/09/2011 29/09/2011 03/10/2011 06/10/2011 13/10/2011 20/10/2011 27/10/2011 Gilbert Street SU 65444 32603 27/09/2011 25/10/2011 Ropley Soke SU 65299 33998 25/10/2011 Soames Farm SU 6450 3050 None collected during test due to early pump failure West End Vale SU 6367 3606 27/09/2011 Drayton u/s outfall SU 59686 33314 27/09/2011 25/10/2011 Drayton discharge SU 59690 33312 25/10/2011 Drayton discharge at outfall 27/09/2011 combined Drayton d/s outfall SU 59645 33313 25/10/2011 Bishops Sutton outfall SU 60492 32292 27/09/2011 25/10/2011 Below Alresford Pond SU 58799 32975 05/09/2011 13/09/2011 15/09/2011 19/09/2011 22/09/2011 29/09/2011 03/10/2011 06/10/2011 13/10/2011 20/10/2011 27/10/2011
4.8.1.1. Standards used for comparison The following standards were used to assess water quality.
EU Drinking Water Standards Directive (DWSD)
This was used to assess PAH concentrations. The limits imposed by the Directive are:
PAH total sum of four should not exceed 0.1ug/l, with the four PAH’s being (benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(123-cd)pyrene).
In addition Benzo(a)pyrene should not exceed 0.01ug/l.
EU Water Framework Directive 2008/105/EC (WFD)
Acenapthene 0.1ug/l
Fluoranthene 0.1ug/l
Benzo(b)fluoranthen with Benzo(k)fluoranthen total 0.03ug/l
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It was difficult to assess some of the PAHs observed at the sites as no limit is listed in the WFD. There are four listed below which are included by the United States Environmental Protection Authority (USEPA) on their list of PAHs, so attention is drawn to them here where they were observed.
Benzo(a)anthracene
Chrysene
Phenanthrene
Pyrene
4.8.1.2. Review of water quality data Axford
Fluoranthene – at start-up (27/09/2011) Axford 1A concentration was 0.0229 ug/l; by 19/10/2011 the concentration had fallen to 0.0166 ug/l, well below 0.1 ug/l limit imposed by WFD.
Total PAH – at start-up, Axford 1A concentration was 0.0729 ug/l, falling to 0.0666ug/l by 19/10/2011; below the 0.1 ug/l limit for four PAHs set for DWSD standards.
Conclusion – none of concern
Bradley
Conclusion – none of concern
Wield
Benzo(b)Fluoranthene and Benzo(k)Fluoranthene were below the total allowable under WFD of 0.03 ug/l on 27/09/2011 at 0.0129 ug/l;
Chrysene – concentration of 0.0129 ug/l measured on 27/09/2011; reduced to <0.01 ug/l by 19/10/2011.
Fluoranthene – concentration fell from 0.0557 ug/l on 27/09/2011 to <0.01 ug/l on 19/10/2011.
Total PAH – decreased from 0.114 ug/l on 27/09/2011 to <0.06 ug/l on 19/10/2011.
Phenanthrene – decreased from 0.0107 on 27/10/2011 to <0.01 ug/l.
Pyrene – decreased from 0.0389 ug/l on 27/09/2011 to <0.01 ug/l on 19/10/2011
Conclusion – although there are measurable concentrations of PAHs none of the concentrations measured exceed the standards used for comparison, so it can be concluded that there are none of concern.
Candover outfall
The Candover outfall was sampled on 27/09/2010 when some of the source sites had PAH concentrations above detectable limits, although not above WFD / DWSD standards.
*Benzo(a)Anthracene – 0.0128 ug/l
Benzo(b)Fluoranthene – 0.0165 ug/l
*Chrysene – 0.0131 ug/l
Fluoranthene – 0.055 ug/l
Total PAH – 0.112 ug/l
*Phenanthrene – 0.0107 ug/l
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*Pyrene – 0.0395 ug/l
*included in USEPA list of PAHs
There is probably only marginal compliance with DWSD total PAH concentration and it is unclear which PAHs are included in the total PAH value reported. The total PAH in the DWSD is for four specific compounds (benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(123-cd)pyrene).
Mass Balance assessment
If a mass balance is calculated for the input PAHs compared to the outfall PAH concentrations then approximately half of the proportion of outfall volume can be attributed to the individual abstraction boreholes, see Table 4-22. The remaining mass observed at the outfall must be due to PAHs derived from the pipeline materials and probably a summation of small, undetected levels at other boreholes.
Table 4-22 Remaining PAH that cannot be attributed to Axford 1A or Wield 3A
PAH PAH concentration remaining Standard for comparison unaccounted for by mass balance (ug/L) Acenapthene 0.0095 0.1ug/l Fluoranthene 0.0288 0.1ug/l Benzo(a)anthrancene 0.0068 No WFD or DWSD Benzo(b)fluoranthene 0.0081 with Benzo(k)fluoranthen total 0.03ug/l Chrysene 0.0071 No WFD or DWSD Phenanthrene 0.0057 No WFD or DWSD Pyrene 0.0214 No WFD or DWSD
As the PAH concentration from the abstraction boreholes reduces with time of pumping it is likely that the PAH derived from the pipeline will also reduce over time. In addition the WFD standards are annual averages and the DWSD is for drinking water so a more rigorous standard than would normally be applied to raw ground and surface water. A further consideration is that the samples collected for the PAH analysis were unfiltered and it is possible that it is disturbance of the pipeline lining at the joints that is causing elevation of PAH in the samples.
4.8.1.3. Temperature Due to the concern over stress to the ecosystem through sudden changes in temperature a programme of regular temperature monitoring was undertaken as part of the test monitoring. Water temperature was measured at the Candover outfall and at Abbotstone on the Candover Stream, as well as at the Alre outfalls at Bishops Sutton and Drayton. Observed temperature readings are provided in Figure 4.21 along with an indication of when the Candover and Alre augmentation scheme boreholes were brought online. The stream temperature at Abbotstone appears to increase as boreholes are switched on which is surprising given the temperature recorded at the outfall is around 10 ⁰C, approximately two degrees lower than the pre-test stream temperature. The thermal regime at the major outfall on the Candover changes dramatically from strong diurnal variations of around 10 - 18 0C to a very constant temperature of around 11oC. This is due to the dominance of the input of the augmentation water to a very small, shallow flow readily influenced by solar radiation.
4.9. Stakeholder engagement An article on the test appeared in the Hampshire Chronicle on 22nd September 2011 and another appeared in the Southern Daily Echo. Copies are provided in Appendix C.4.
The cress bed operators advised the Environment Agency that they knew when the pumps were switched on as they witnessed a reduction in flows (Alison Matthews, pers comm.).
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Some local landowners had shown an interest in the test and were generally welcoming of the additional flows in the river provided by the augmentation (Alison Matthews, pers comm.).
4.10. Revised conceptual understanding The testing does not appear to indicate any need for changes to be made to the conceptual understanding of the area. The high transmissivity calculated for the pumping tests on the Alre boreholes and the very rapid impact on groundwater levels observed at the cress beds provides additional evidence for the known high transmissivity, low storage zone associated with this area.
The transmissivities calculated from this testing are lower than those previously calculated and this may be attributable to differences in start rest water levels and less favourable test conditions in terms of duration of early test and interference effects.
The poorer regression relationship between Drove Lane and Sewards Bridge (seen in this test and previously in 1989) is probably attributable to the larger groundwater catchment compared to surface water for Drove Lane and the local hydrogeological configuration (very high transmissivity), which is significantly different to the catchments for the Cheriton Stream (Sewards Bridge gauge) and the Candover Stream (Borough Bridge gauge). The poorer relationship between the Easton gauge (Itchen) and Sewards Bridge may reflect the influence of the Alre catchment input and the nature of the influence on river flows of the Easton abstraction.
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Itchen Implementation NEP Scheme 5. Conclusions & Recommendations
This section of the report brings together key conclusions from the previous sections of the work in the context of how either or both of the augmentation schemes might provide water resource benefits for the supply-demand balance of the next Water Resources Management Plan (WRMP14) and Periodic Review (PR14). This section also sets out some regulatory and operational issues that will need to be resolved before the augmentation schemes could be considered as feasible options for WRMP14.
This report explains the conclusions of the test pumping of Autumn 2011; it does not describe how the augmentation schemes could be used to support the supply demand balance in Southern Water’s Hampshire South Water Resource Zone. These opportunities will be addressed as part of continuing water resource planning work.
5.1. Overview of success of testing programme in meeting project objectives The pumping tests of the Itchen augmentation schemes were successful and met the objectives; these objectives are summarised here together with the outcomes from the investigation.
5.1.1. To confirm, (or otherwise), whether the augmentation schemes can deliver the licensed quantities. Neither augmentation scheme currently appears to be able to deliver its licensed quantity; the output achievable for the Candover scheme appears to be 27 Ml/d, compared to a licence of 36 Ml/d and for the Alre scheme the output is probably about 54 Ml/d compared to the licence of 56 Ml/d. However there are additional environmental constraints that would restrict the benefit to the supply-demand balance and hence the viability of either or both schemes as viable water resource schemes.
5.1.2. To confirm the net gain in the flow of the River Itchen at Allbrook & Highbridge gauging stations for a prolonged period of operation of the augmentation schemes during low-flow periods. The net gain in the flow of the River Itchen for all the gauging stations including Allbrook & Highbridge has been calculated over the six week period of the test pumping. The test pumping was undertaken during a period of low river flows and low groundwater levels. The results are in good agreement with those calculated for the test pumping undertaken in 1976 (Candover) and 1989 (Alre). For adjusted estimated natural flows, the net gain is assessed as: Candover at Borough Bridge - 86%; Alre at Drove Lane ~50%; Itchen at Easton – 83%; Itchen at Allbrook & Highbridge – 78% (see
).
5.1.3. To investigate constraints in the deployable output of each augmentation scheme and to identify whether these could be removed by asset maintenance and/or replacement. Constraints have been identified that restrict the output of the schemes and therefore limit their potential contribution to maintain the supply-demand balance and hence to be considered as feasible water resource schemes. Some of these constraints relate to asset infrastructure, but more are related to less easily manageable challenges such as ecological factors and the impact on other water users.
Section C 2.9.2 of the Environment Agency Site Action Plan (October 2007) identifies “Option 2 – Modify Licences to meet environmental outcomes and to include a Section 20 Water Resources Act 1991 arrangement” as the appropriate option to meet the requirements of the Habitats Directive Stage 4 Review of Consents. Implementation of Option 2 would require the following licence changes:
• Modify Candover Scheme licence to include a condition restricting use to Hands Off Flows of 198 Ml/d at Allbrook & Highbridge or when flows at Riverside Park fall below 194 Ml/d.
• Replace condition in Alre Scheme licence with tiered MRF condition with a condition restricting use to Hands Off Flows of 198 Ml/d at Allbrook & Highbridge or when flows at Riverside Park fall below 194 Ml/d.
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• Modify Candover Scheme licence to restrict daily abstraction to 20 Ml/d between 1st May and 31st August.
• Include conditions in both licences to refer to section 20 operating agreement.
The constraints to operating the sources for supply demand benefits that would arise from implementation of the SAP conditions are listed below, together with any identified solutions:
5.1.3.1. Site Action Plan (SAP) constraint on Candover 1st May to 31st August, output limited to 20 Ml/d The purpose of this flow condition is to protect the native crayfish population from any large increase in flow velocity resulting from discharge from the augmentation scheme outfall which could result in them being washed downstream. If the discharge point were to be relocated downstream of the crayfish habitat area then this may be unnecessary. Note that Section C.2.9.2 of the SAP considers that Option 3 – Construct Additional Infrastructure and Apply Target Flow Conditions “…does not seem a fair and reasonable approach when implementing operating rules can meet the environmental outcomes of the site at a lower cost.”
5.1.3.2. Minimum flow conditions for start up for Alre, and in practice also the Candover scheme - 1st February to 31st March, at or below 280 Ml/d, 1st April to 30th November, at or below 240 Ml/d, 1st December to 31st January, at or below 300 Ml/d Flow conditions are written into the Alre abstraction licence but there are no similar conditions that apply to the Candover abstraction licence. In practice EA follows similar flow thresholds in its operation of the Candover scheme. The SAP states that in the future the Candover licence would have a low flow trigger of 198 Ml/d at Allbrook & Highbridge or 194 Ml/d at Riverside Park. Strict application of that trigger would restrict operation of the scheme and hence its feasibility as a viable water resource scheme.
5.1.3.3. Slow ramp up and ramp down due to ecological constraints This is an advisory regime to ensure a gradual increase in flow velocity and gradual temperature reduction in order to protect the native crayfish. If the discharge point were to be relocated downstream of the crayfish habitat area, then this might be unnecessary.
5.1.3.4. Likely future requirement for ecological survey prior to scheme start-up (Candover scheme) Following the uncertainty in relation to crayfish health prior to the 2011 test, EA ecologists have indicated they are likely to require surveys prior to scheme switch on to ensure no damage occurs to the crayfish population through operation of the Candover scheme. The need for this might be avoided if the discharge for the scheme were to be relocated to downstream of the crayfish habitat.
5.1.3.5. Impact on cress beds at Bishops Sutton (Alre scheme) Operation of the Alre scheme causes a rapid reduction in spring and river flow at the cress beds. To compensate for these effects, the cress bed operators divert flow from the augmentation scheme outfall into the cress beds. Although the water is returned to the river, losses from the cress beds and through the river bed mean that the net gain calculated for Drove Lane is only approximately 50%. It might be possible to abstract at a reduced, sustainable rate and reduce the impact on the spring flow if it is dependent on not dewatering a particular geological horizon, but this would require further investigation following the installation of more sensitive controls such as variable speed drives on the borehole pumps and is beyond the scope of the current investigation. It is possible the Environment Agency may wish to consider investigating this as part of future decisions about the Alre augmentation scheme.
5.1.3.6. Unknown and unpredictable diversion of flows by cress bed operators on Alre scheme The way flows are managed at the cress beds by the operators is currently unknown and the flows are not routinely measured. Decisions over which valves and/or sluices to open are not controlled by any agreed operating procedure. The magnitude of the impact on the flow downstream is not known. The cress bed operators have indicated to the EA that after October their operations tend to move overseas so their reliance on spring flows during the winter period may become less critical however where possible they still intend to get a crop from the site.
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5.1.3.7. Candover pipeline constraint means output is limited to approximately 27 Ml/d (field test) compared to licence of 36 Ml/d, although pipeline model suggest theoretical capacity of about 33 Ml/d Field tests indicated that the maximum output achievable for the Candover scheme is limited by the pipeline, although the pipeline model suggests the theoretical capacity should be higher than this. The uncertainties in the pipeline model are around the pump capacities and pump curves, so confidence in the pipeline model could be improved if all pump details could be established. The field tests also highlighted the difference in calculated flow using the sum of individual flow meters compared to the measured total output at the outfall. It is unclear whether the errors associated with using individual flow meters are due to the age of the flow meters or back-pressure effects from the pipeline.
5.1.3.8. Manual inspection and start-up requirements, resulting in slow response time if incidents occur Due to an inability to remotely start-up and monitor the augmentation schemes they require a site visit for start-up and daily inspection during use. This is very labour intensive and in addition means that any shut down or problem that occurs may take 24 hours to rectify or be acted on.
5.1.3.9. Possible water quality issues associated with pipeline construction on Candover scheme There appears to be some PAH quality problems at some of the Candover sites. At the time of construction it was usual practice to use a bitumen related product to coat the borehole casing or seal pipe joints. This is no longer undertaken in the water industry due to the recognition of the PAH problem caused when the product decays. It is possible that the PAH observed in the water samples collected before and during testing is coming from the joint seals. Although the concentrations are low and within currently defined standards, in part due to dilution, it is possible that in the future standards may be tightened. It may be prudent to review whether upgrading of the pipeline to modern standards is advisable.
5.1.4. To assess the condition of the M&E assets and what will be required to bring them up to the operational reliability and flexibility required of strategic augmentation boreholes used to maintain public water supplies. The assets have been inspected and graded according to Southern Water’s standards and OFWAT grading. The major upgrade that would be necessary to enable them to achieve the operational reliability and flexibility required of strategic augmentation boreholes used to maintain public water supplies are:
Installing pressure transducers to monitor pumped water levels; Installing variable speed drives (VSD) to improve control of pumping rates; and Installation of telemetry (either phone, radio or satellite as appropriate) to allow remote operation and management.
5.2. Asset suitability for support for public water supply The following recommendations are made for further work to fully understand the Candover pipeline:
It would be prudent to re-survey the pipeline to confirm the locations and specifications of the air valves, particularly if any further hydraulic modelling/surge analysis is to be undertaken. Pressure testing of the main should be undertaken to rule out any leaks. The Kent Helix flow meters should be replaced and any new flow test results compared to the figures produced by the modelling. The boreholes pumps should be inspected to obtain the manufacturer and serial number to confirm their performance characteristics.
Additional points are made here in relation to the summary in Section 5.1.
5.2.1. Telemetry The schemes are currently operated manually and this limits their flexibility and the efficiency with which they can be brought into service. Telemetry for remote operation and monitoring would be necessary for the scheme to be able to fully support river flows, which in turn support public water supply abstractions. The sites located in the Candover Valley do not currently have a mobile phone signal. Discussions have been
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Itchen Implementation NEP Scheme held with Wireless Innovations who currently supply the satellite communications telemetry at the Otterbourne Water Supply Works and they have confirmed that minimal alterations would be required for the additional input from the schemes at the Otterbourne hub. Their initial thoughts are that a local radio network for the Candover sites would offer the best solution with a single satellite communication point for the three sites; however this would be subject to confirmation following a survey. The Alre valley has a better mobile signal so this, or landlines, would offer a cheaper solution; however a similar set-up with a radio network and satellite signal would also be feasible here.
5.2.2. Vibration and stator temperature monitoring of the pumps Alterations to the panels should be made to allow vibration and stator temperature monitoring of the pumps during operation. This would bring the scheme into alignment with Southern Water standard practice. Similarly water level transducers should be installed to allow monitoring of pumped water levels, as currently only pump cut-offs are installed.
5.2.3. Variable speed pumps The installation of VSDs on the panels would allow for better control of the abstraction rate, particularly for the ramp down period and the abstraction boreholes in the Alre scheme. Following the test in 2011 during the ramp down period the Environment Agency eventually installed a temporary VSD in order to allow some natural recharge to occur while they were trying to balance the conflicting requirements of providing a flow for the cress beds and turning the scheme off. A VSD was also used during the refurbishment of the Alre pipeline in June 2011 as the infrequent use of the scheme raised concerns that if it was started up at full output this could cause problems with pipeline bursts or valve failure.
5.3. Issues around ecology The HIWWT report concludes that the testing of the Candover Stream and River Alre flow augmentation schemes in autumn 2011 resulted in immediate and significant modifications in flow rates and water levels at two regionally important locations for the nationally and internationally endangered white-clawed crayfish.
Information and analysis of data collected during this test led to HIWWT making the following recommendations about future use of the schemes:
Ramping-up of the operation of the Candover Stream scheme should be undertaken considerably more slowly in small, regulated flow rate increases; The maximum operating output of the Candover Stream scheme should be reviewed to ensure that, under typical operating conditions, the resultant flows are not uncharacteristic of flows which could naturally be observed downstream of the discharge point; Use of the scheme as a rapid-response solution to short-term deficits or periods of high demand is inappropriate; Habitat improvements should be made on both tributaries, particularly between and downstream of the two Candover survey sites, to mitigate any undetected drift of crayfish caused by use of the schemes; Preparatory actions, such as channel maintenance and weed cutting, must be undertaken before any future use of the schemes; and Ecological monitoring (including water quality analysis and crayfish monitoring) should be carried out prior to and throughout all future operations. This will allow for the detection (if present) of any adverse impacts and should result in the suspension of the scheme if necessary.
The HIWWT report also notes that if used sensitively, the operation of the Upper Itchen flow augmentation schemes during periods of extreme drought would benefit fish, white-clawed crayfish, and other aquatic invertebrates by providing a secured supply of water essential for their survival.
5.4. Other considerations
5.4.1. Cress bed operators The impact of abstraction on the cress beds from the Alre scheme is even more rapid than previously thought. Although the pipelines and off-takes were installed to mitigate this impact, the cress bed operators quickly become heavily reliant on the discharge from the augmentation scheme outfalls once the natural spring flow diminishes. The operational management of the valves and/or sluices at the cress beds is not
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Itchen Implementation NEP Scheme well understood and the volumetric effects unknown, so it is not clear whether this type of operation impacts on the efficiency of the scheme.
5.4.2. Resilience The Alre scheme has two boreholes on each pipeline. If one borehole fails, this can lead to a significant reduction in discharge to the river and hence flows into the cress beds. Because operation of the augmentation scheme will have already reduced natural spring flows and stimulated the cress bed operators to divert discharges from the augmentations schemes, failure of the augmentation scheme reduces the resilience of continued supplies to the cress beds.
5.4.3. Water quality Although considered of low risk, the presence of PAHs in the discharge water for the Candover scheme would need to be monitored and the possibility of pipeline replacement to remove what is thought to be the source at pipe joints may need to be considered.
5.5. Recommendations
5.5.1. Candover The Candover augmentation scheme provided a sustained output of around 27 Ml/d for the six week duration of the 2011 test. Bradley and Wield are the highest yielding sites, apparently able to sustain approximately 17 Ml/d and 15 Ml/d respectively for the groundwater levels at the time of the test. The pipeline capacity appears to limit the scheme output. The recommendations in the Site Action Plan (SAP) would restrict abstraction to 20 Ml/d over the period from 1st May to 31st August. The SAP also recommends the introduction of a MRF flow condition of 198 Ml/d and slow ramp-up to avoid rapid changes in temperature and flow regime. Although no time-frame is specified for the slow ramp up, it is likely to take approximately two weeks to achieve full output for the scheme.
The net gain was assessed for the combined Alre and Candover schemes at Allbrook & Highbridge as approximately 78%. At Borough Bridge, i.e. only the Candover scheme, the net gain was calculated as approximately 86%.
Work needs to be undertaken to bring the scheme onto a telemetered system and this is likely to involve a satellite / wireless solution due to poor / absent mobile phone signal in this valley. This is not considered particularly onerous as the existing hub at Otterbourne has spare capacity for the scheme to use (pers comm. Paul Williams, Wireless Innovation). Some minor reconfiguration of the hub would be necessary.
Panel changes would be needed at each site to bring them up to Southern Water standards, pumps should be lifted and checked and water level transducers and VSD’s installed. Some upgrading of the pipeline may be necessary to remove PAH sources from pipe joints; this is not considered immediately necessary.
5.5.1.1. Constraints summary The following provides a bullet point summary of the key constraints identified by this investigation for the Candover scheme in terms of taking it forward to use as support for public water supply support:
Licence 36 Ml/d Source potential output 36 Ml/d, according to 1976 testing of individual boreholes. Pipeline constraint 27-30 Ml/d SAP constraint 20 Ml/d May-August (inclusive) SAP constraint 198 Ml/d MRF at Allbrook & Highbridge (this flow is only likely to be reached during very low flow or drought years) SAP constraint (approximately) two week ramp-up time
5.5.1.2. Other limitations Currently manual operation only; requires telemetry with wireless system Panels require upgrade, VSD, temperature monitoring for pumps Boreholes require water level transducers Outfall requires flow measurement and telemetry, level monitor downstream Will require pre-use crayfish survey
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5.5.1.3. Options for use In order to avoid the May – August restrictions, the main outfall from the scheme could be relocated downstream of the crayfish habitat, thus allowing the current 27 Ml/d output to be delivered into the Itchen. If the pipeline capacity were increased, the licence quantity of 36 Ml/d could in theory be delivered, although this has not been tested in practice.
This may give rise to an estimated net gain at Allbrook & Highbridge of approximately 20 Ml/d or 27 Ml/d. In addition, the relocation of the outfall would mean that the ramp up time could be reduced.
5.5.2. Alre The Alre scheme appears to be able to deliver slightly under its full licensed quantity, although the failure at Soames Farm early on in the 2011 test means that it wasn’t tested for an extended period. The rapid expansion of the cone of depression has to be a limit on the use of this scheme at its currently licensed quantity; it has an almost immediate and significant impact on the cress bed operators at Bishops Sutton and although this is mitigated by the pipeline and valve operation available to them, it also impacts on the flows in the river Alre, resulting in a net gain of approximately only 50%, even with only six weeks of abstraction.
The cone of depression also spreads out towards the Cheriton stream and although during the 2011 testing it was not observed to have had a significant impact on levels very close to the Cheriton it is estimated that with approximately a further two weeks of abstraction, the Cheriton flows would have been impacted.
It may be useful to undertake an extended constant rate pumping test at lower rates of abstraction, extended borehole step pumping tests, combined with further analysis of the geological structure and spring elevations to investigate the possibility of abstracting at lower, possibly more sustainable rates but this is beyond the scope of the current investigation. This might mean that a key productive horizon, linked to spring flow, does not become dewatered and may be a management option the Environment Agency would be best placed to investigate. However, the fact that drawdown observed in the abstraction boreholes is approximately 4-6 m with 14 Ml/d of abstraction suggests this may not be possible.
The net gain at Drove Lane, i.e. for the Alre scheme alone, was calculated at approximately 50%.
As with the Candover scheme, work would need to be undertaken to bring the Alre scheme onto a telemetered system. Unlike the Candover Valley there is mobile signal coverage for the Alre so a satellite / wireless solution is unlikely to be necessary.
Panel changes would be needed at each site to bring them up to Southern Water standards, pumps should be lifted and checked and water level transducers and VSDs installed.
5.5.2.1. Constraints summary The following provides a bullet point summary of the key constraints identified by this investigation for the Alre scheme in terms of taking it forward to use as support for public water supply support:
Licence 56 Ml/d Various MRF levels through the year before switch on are currently in the licence; - 1st February to 31st March, at or below 280 Ml/d, - 1st April to 30th November, at or below 240 Ml/d, - 1st December to 31st January, at or below 300 Ml/d; but these may be simplified to 198 Ml/d according to SAP.
5.5.2.2. Other limitations Impact on cress bed operators and possibly other boreholes Relatively low net gain Rapid expansion of cone of depression to impact on River Alre, Candover Stream, Cheriton stream and River Meon Currently manual operation only; requires telemetry with wireless system Panels require upgrade, VSD, temperature monitoring for pumps Boreholes require water level transducers Outfall requires flow measurement and telemetry, level monitor downstream
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5.5.2.3. Options for use It may be possible to utilise the Alre scheme at lower abstraction rates to prevent dewatering of key hydrogeological horizons. The intention would be to improve net gain by reducing the impact on stream flow and reduce the impact on cress bed operators. This would require further investigations which are beyond the scope of this investigation and are more likely something the Environment Agency would be better placed to undertake in order to manage the scheme in the future.
5.5.3. Potential for use as water resource schemes Under the current Water Resource Planning Guideline the supply-demand balance to be used for Water Resource Management Plans (WRMP) is calculated for specific design conditions, namely Deployable Output and unrestricted “dry” year demands; the design conditions could be protracted periods of dry weather, and as shown by the 2011-2012 drought extend to more than one dry winter.
So unless the schemes could be operated in successive years, they cannot in the context of the current WRMP be considered to be viable water resource schemes. The schemes could however have potential to mitigate adverse environmental conditions in the catchment upstream of SWS Lower Itchen abstractions during severe droughts.
Whilst the pumping tests have shown that each scheme can provide some water resource benefits, there are various additional constraints that would also need to be overcome before either, or both, schemes could legitimately be considered to be capable of contributing to the supply demand balance. The relatively small net gain and the derogations to other licence holders mean that the Alre scheme in its present form is not considered to be a viable water resource scheme; the following sections therefore refer to the Candover scheme only.
5.5.3.1. Abstraction licence conditions The current abstraction licences and the proposed changes set out in the Site Action Plan (SAP) would need to be reviewed to take account of the following:
Appropriate control procedures (to be incorporated into a water resources management agreement), based on downstream flow conditions that would provide sufficient operational flexibility for a source that supports public water supplies across a range of hydrological conditions; and All of the net gain to flow from the scheme outfall would be available for abstraction further downstream at the Otterbourne intake.
The abstraction licences would then need to be amended as appropriate.
5.5.3.2. Other considerations The likely requirement for a pre-operation ecological survey of crayfish and the possibility that this could restrict the operation of the scheme completely means that the scheme cannot be relied upon under the design conditions required for the WRMP. The only alternative would be for a new discharge pipeline and outfall to be located downstream close to the confluence of the Candover Stream with the River Itchen, thus avoiding the crayfish habitat.
The ownership and responsibility for operation of the schemes will need to be addressed. Suitable allowances for the carbon costs associated with operational pumping will need to be made in the annual carbon budget.
5.5.3.3. Assumptions for water resource planning Further assessment and agreement by EA of the following assumptions on the potential use of the Candover Scheme would be required before it can be considered as a sufficiently risk-free option for the current round of water resource planning:
The Candover scheme can provide a net gain at Allbrook & Highbridge of up to 20 Ml/d during the MDO period from September. The 2011 tests suggest that this average level of net gain can be sustained for a period of at least eight weeks, but would then probably gradually reduce; The Candover scheme can be operated over a number of successive years; There is no PDO benefit; The full net gain to flow from the scheme is available for abstraction at the Otterbourne WSW; The ownership and operational responsibility for the Candover scheme is transferred from the EA to SWS;
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Operation of the scheme is not curtailed by the health of the population of white clawed crayfish located in the Candover catchment.
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Itchen Implementation NEP Scheme References
Giles D. M. and Lowings, V. A. (1989) Variation in the character of the Chalk aquifer in East Hampshire. Proceedings of the International Chalk Symposium, 4-7 September 1989, Brighton Polytechnic
Southern Water Authority (1979). The Candover Pilot Scheme Final Report
Southern Science (1991). Report on the 1989 Test Pumping of the Alre Scheme
Southern Science (1992) Report 92/6/450 Test and Itchen Groundwater level analysis
Southern Water (1985). Further Itchen River Augmentation Scheme, 1984 Test Pumping Analysis
Environment Agency (unknown). Augmentation Scheme Testing, Autumn 1997
Environment Agency (2007). River Itchen SAC ROC Stage 4 Site Action Plan: Water Resources Part A, B and C
Atkins 1996. River Itchen Augmentation Scheme Survey Phase 1 – Candover Pipeline, for National Rivers Authority, Southern Region. Report reference AK1935/122/DO/013
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Appendices
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Appendix A. Asset Survey
A.1. Data Collection The Request For Information (RFI) spreadsheet was updated with information collected from the site visit.
A.2. Site Visit Alex Murchie (Mechanical Engineer) and Brian Smith (Electrical Engineer) visited the four Alre and three Candover borehole production sites, accompanied by Trevor Sim and Neil Terry, a MEICA engineer from the Environment Agency on the 2nd of June 2011. Each installation was visually inspected, including opening of electrical panels and lifting of covers, where possible, by Neil Terry.
A.3. Desktop Study A desk study of the information gathered for the sites has been undertaken following the site visits to identify any constraints in deploying the Itchen NEP Implementation Scheme, including the planned step tests.
A.3.1. Condition Assessment A condition assessment of each piece of equipment was made and an OFWAT condition and performance grade assigned; this is recorded in the RFI spreadsheet.
The condition of the visually inspected equipment was found to be reasonably good and would not be expected to hold back the proposed testing or NEP Implementation Scheme itself. It should be noted that the Candover and Alre schemes were not inspected in their entirety; some equipment such as the pumps are not readily visible and could not be assessed; other equipment could not be assessed due to lack of access and time constraints.
The typical design life for M&E equipment supplied to the water industry is given below (taken from Southern Water MED 4001):
General Mechanical and Electrical 20 years Gearboxes 100,000 hours Bearings (L10) 100,000 hours Other mechanical moving parts 50,000 hours Centrifuges and drum thickeners 20,000 hours Boilers, flare stacks &gas burners 15 years Sludge heat exchangers 15 years Progressing Cavity Pumps 15 years Submersible pumps less than 7.5 kw 10 years Submersible pumps greater than 7.5 kw 15 years Cutter pumps 15 years All other pumps 20 years Screens & screenings handling 20 years Conveyors 15 years Blowers & compressors 20 years Ventilation equipment 15 years Below ground valves 50 years All other valves 20 years Control Panels & Motor Control Centres (MCCs) 20 years PLCs & SCADA 10 years ICA (Instrumentation) 15 years Switchgear 25 years Variable Speed Drives 15 years Detectors (gas, fire, intruder) 10 years CCTV 10 years Batteries 3 years Lightning protection 40 years Lighting – external Int, 15 years, Ext 10 years
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Coating lives shall be in accordance with BS EN ISO 9514
These design lives are referenced in the following equipment subsections and a view on likely replacement dates is given where possible. It should be noted that the low usage required of the schemes may extend the equipment lives in some cases, particularly if wear is the main cause of degradation.
A.3.1.1. Pumps The borehole pumps on the Candover scheme were originally installed circa 1975. The information gathered from the site O&M manuals is referenced in the RFI spreadsheet. It is understood that the original pumps may have been replaced or refurbished. Assuming this took place in 1990 from a typical asset life of 15 years, the pumps could need replacing again shortly. However, the hours run figures are very low for all the Candover production sites which indicates that wear would probably not be a concern.
The borehole pumps on the Alre scheme were originally installed circa 1984. It is understood that the original pumps may have been replaced or refurbished. If this took place in 1999 they may need replacement shortly.
The particular concern with the Alre pumps is that they have not been run for at least 5 years which may have resulted in some components degrading and becoming unreliable. The EA have engaged Integrated Water Services to restart the pumps using variable speed drives. This will be undertaken as a re- commissioning procedure and it is envisaged that the borehole pumps will be run using their fixed speed, soft starters thereafter. During the re-commissioning the pump speed will be gradually increased up to the design duty to minimise the wear on the pump bearings and possible surge pressures. This will help minimise any potential damage to the pumps and pipeline.
A.3.1.2. Valves Where inspected, valves appeared to be in reasonable condition. It is assumed that the currently installed valves are the original items installed on all sites. The available information does not indicate otherwise. Valves have a typical 50 year design life which should mean they would not require replacement until approximately 2024 for Candover and 2034 for Alre.
Maintenance to ensure correct operation of air valves is particularly important to avoid high surge pressures and subsequent damage to pipelines. The air valves on the Bighton Valley and Bishops Sutton pipelines should be maintained regularly to ensure correct operation. It is understood that the air valves on the Alre scheme are being replaced by the EA before the testing as a matter of course.
A.3.1.3. Pressure Vessels The Alre scheme production sites incorporate pressure vessels for surge pressure suppression. These appear to be in good condition.
The EA has an inspection regime in place as required under The Pressure Systems Safety Regulations 2000. The vessels should be verified and inspected by a UKAS Accredited Type-A Inspection Body in accordance with ISO/IEC 17020. The test certificates were not available during the site visit; these should be obtained before any testing commences.
A.3.1.4. Flow Meters All the production boreholes have Kent Helix bulk flow meters fitted. It is not known if these are serviceable. The Alre sites have pillar mounted pulse meters. It is understood that the original items have been replaced with new and these appeared to be in good condition.
A.3.1.5. Panels The original panels on the Candover production sites have been replaced with those procured from Barden Control Systems circa 1999 and are in good condition. Given a 25 year design life for switchgear these would be expected to remain operable until 2024.
The Alre scheme panels procured from Barden Control Systems are in reasonable condition. These were installed in 1996. Some corrosion was apparent at the base of the Soames Farm panel which should be treated and the kiosk checked for leaks/water ingress.
A.3.1.6. Kiosks The kiosks on all production sites appeared to be in a reasonable state of repair.
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A.3.1.7. Instruments The only field mounted instruments apparent on the boreholes are low level electrodes, fitted for pump protection. No assessment of the condition or performance of these could be made as they are not readily visible. It is likely that they are the original items, in which case they would be expected to need replacement.
A.3.1.8. Outfall Structures Only the major Candover and Alre outfall structures were visited. They consist of a concrete channel with crump weirs with adjacent measuring well and chart recorder.
There is a telemetry kiosk at the major Candover outfall but it was not possible to obtain access during the site visit or confirm that a PSTN telephone line was still connected. The EA advise that the system is not operational (Neil Terry pers comm.).
Considerable plant growth was observed in Alre major outfall channel. It is recommended that this is removed along with any silt.
Due to the dilapidated appearance it is recommended that both the Alre and Candover major outfalls have new level measuring and telemetry systems installed.
A.3.1.9. Comparison with Southern Water Standards A high level comparison of the main M&E equipment installed at the production sites has been made against the requirements of Southern Water’s MED Specifications to gauge compliance. It is not envisaged that departures from Southern Water’s MED Specifications will need rectifying unless they present a significant operational or H&S problem for Southern Water.
Specifications used:
MED4100 Valves MED4120 Pressure Vessels MED4155 Borehole Pumps MED4300 LV Switchgear & Controlgear Assemblies Rated Above 100A. MED4303 Power Factor Correction and Harmonic Limitation
A.3.1.10. Valves No significant departure from MED4100 was identified.
Section 2.2.2 states that butterfly valves shall not be installed below ground: The Candover borehole sites incorporate butterfly valves installed in below ground chambers, however it would not seem necessary to rectify this as there are also in-line gate valves provided for isolation.
A.3.1.11. Pressure Vessels No significant departure from MED4120 was identified but it should be ensured that the EA have evidence that all vessels are verified and inspected by a UKAS Accredited Type-A Inspection Body in accordance with ISO/IEC 17020. This should be obtained before any testing begins.
A.3.1.12. Borehole Pumps No significant departure from MED4155 was identified.
Section 2.5 requires condition monitoring of the pump; specifically vibration and stator temperature monitoring. This cannot be achieved without modification to the pumps, panels and undertaking the telemetry scope identified for each site in Section 4 of this technical note.
A.3.1.13. Electrical Panels No significant departure from MED4300 or MED4303 was identified. However the following modifications would be required to make the panels more compliant. This is applicable to all sites.
1. Replace panel door locks with triangular key type 2. Fit kWh meter to each panel 3. Install test facility for starters
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4. Install portable tool 110V supply from each panel 5. Install power factor correction in each panel
A.3.2. Telemetry and Automation Currently all of the sites can only be operated manually and there is no telemetry facility. Pumps must be started manually, valves adjusted to provide the desired flow rate and boreholes dipped to measure water levels.
Due to the lack of time available before the proposed step testing programme it is not thought feasible to install a telemetry system for the purpose of monitoring the testing if the current programme is to be adhered to. It may be possible to install a temporary data-logging system to record information such as borehole flows and levels before the proposed net gain testing.
Steve Tough is the Southern Water ICA and SCADA manager for the west Hampshire area. After discussing the potential telemetry strategy for the sites with him it is envisaged that the following scope of works would be required at to meet Southern Water’s requirements.
Scope for production sites:
1. Interposing relays installed in panel to start/stop the pump over telemetry 2. Interposing relays installed in panel to show plant status and send alarms over telemetry 3. The installation of a magnetic flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry. 4. The installation of an ADSL router and telemetry outstation. 5. The installation of a level transducer in the borehole in order to provide an analogue signal to telemetry, as there appears to be only a level electrode fitted. 6. BT contacted to provide the necessary line installation from the existing telegraph pole at site (where telephone line available and economical). 7. Wireless Innovations to provide satellite communications (where telephone line unavailable or uneconomical) 8. Configuration of system on SCADA at Testwood control room It is not envisaged that automation, which would allow each system to work to a flow set point, would be required, however the following additional items could be provided to achieve this.
1. The installation of a VSD to replace the soft starter in the space available at the back of the existing MCC, in order to control the speed of the pump. 2. Installation of and programming of PID controller within the existing panel Scope for outfall and observation borehole sites:
1. Installation of ultrasonic head and transmitter 2. Installation of ADSL router and telemetry outstation in GRP enclosure 3. BT contacted to provide the necessary line installation from the existing telegraph pole at site (where telephone line available and economical). 4. Wireless Innovations to provide satellite communications (where telephone line unavailable or uneconomical) 5. Power supply from REC. Alternatively a battery powered data logger system could be used.
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A.4. Site survey information
A.4.1. Alre scheme Pump Isolation NRV Air Valve Accumulator Flowmeter Panel Level Dip tubes Hours run Notes Valve/s electrode Soames I2 Borehole DN250 Not fitted Fitted Fitted volume DN250 Kent helix Form4 type Low level Not Pump not run Farm submersible Butterfly unknown bulk meter with with 630A electrode observed for 6 years 194kW GRP enclosure fused wiring fitted mounted pulse incomer meter section, panel mounted 400A fused soft start Gilbert H3 Borehole DN300 DN300 swing Fitted Not fitted DN300 Kent helix Form4 type Low level Not Pump not run Access under Street submersible Butterfly from check from according to according to bulk meter with with 630A electrode observed for 6 years covers not 194kW records records O&M records O&M GRP enclosure fused wiring fitted possible keys not mounted pulse incomer available - plant meter - from section, information records panel obtained from site mounted O&M. Pump not 400A fused run for 6 years soft start Ropley G3 Borehole DN300 DN300 swing Fitted Fitted DN300 Kent helix Form4 type Low level Not Pump not run Access under Soke submersible Butterfly from check from according to according to bulk meter with with 630A electrode observed for 6 years covers not 194kW records records O&M records O&M GRP enclosure fused wiring fitted possible mounted pulse incomer difficulties meter - from section, removing covers - records panel plant information mounted obtained from site 400A fused O&M. Pump not soft start run for 6 years West End F4 Borehole DN250 DN250 swing Fitted Fitted DN250 Kent helix Form4 type Low level Not Pump not run Access under Vale submersible Butterfly check from according to according to bulk meter with with 630A electrode observed for 6 years covers not 171kW records O&M records O&M GRP enclosure fused wiring fitted possible stinging mounted pulse incomer nettles meter - from section, surrounding records panel padlocks - plant mounted information 400A fused obtained from site soft start O&M. Pump not run for 6 years
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A.4.2. Candover Scheme Pump Isolation NRV Air Accum Flowmeter Panel Level electrode Dip tubes Hours run Notes Valve/s Valve ulator
1A Borehole DN150 DN150 swing Fitted Not DN150 Kent helix Form4 type Low level electrode Observation 1687 hrs run Panels replaced Axford submersible Butterfly, check fitted with panel wiring fitted borehole for since 1999 1999. Original bulk meter 66kW DN150 mounted soft dipping pumps have been Wedge Gate starter. replaced but no record of dates. 1687 hrs run since 1999 1B Borehole DN150 DN150 swing Fitted Not DN150 Kent helix Form4 type Low level electrode submersible Butterfly, check fitted bulk meter with panel wiring fitted 66kW DN150 mounted soft Wedge Gate starter Bradley 2A Borehole DN150 DN150 swing Fitted Not DN200 Kent helix Form4 type Low level electrode Not observed 397 hrs run Panels replaced submersible Butterfly, check fitted bulk meter with panel wiring fitted since 1999 1999. Original 150kW DN150 mounted soft pumps have been Wedge Gate starter replaced but no record of dates. 397 hrs run since 1999 2B Borehole DN150 DN150 swing Fitted Not DN200 Kent helix Form4 type Low level electrode submersible Butterfly, check fitted bulk meter with panel wiring fitted 150kW DN150 mounted soft Wedge Gate starter Wield 3A Borehole DN150 Not fitted Not Not DN200 Kent helix Form4 type Low level electrode Observation 558 hrs run Panels replaced submersible Butterfly, fitted fitted bulk meter with panel wiring fitted borehole for since 1999 1999. Original 150kW DN150 mounted soft dipping pumps have been Wedge Gate starter replaced but no record of dates.558 hrs run since 1999 3B Borehole DN150 Not fitted Not Not DN150 Kent helix Form4 type Low level electrode submersible Butterfly, fitted fitted bulk meter with panel wiring fitted 90kW DN150 mounted soft Wedge Gate starter
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A.5. Condition Assessment
1. Condition Grading All the sites in the programme were visited at least once and information on condition and performance grading recorded on data log sheets. This information is included in Appendix A.5.2.1 and A.5.2.2.
The following condition grading allocations from OFWAT were used:
1. Sound modern structure with modern mechanical and electrical plant and components that are well maintained. 2. As 1, but showing minor signs of deterioration. Routine refurbishment and maintenance required with review of condition in the medium term. 3. Functionally sound but appearance significantly affected by deterioration, structural is marginal in its capacity to prevent leakage, mechanical and electrical plant and components function adequately but with some reduced efficiency and minor failures. Review of condition required during the medium term. 4. Deterioration has a significant effect on performance of asset, due to leakage or other structural problems, mechanical and electrical plant and components function but require significant maintenance to remain operational. The asset will require major overhaul/replacement within medium term. 5. Serious structural problems having a detrimental effect on the performance of the asset. Effective life of mechanical and electrical components exceeded and incurring expensive maintenance costs compared to replacement cost due to unreliability. The asset will require major overhaul/replacement in the short term.
Assets of grade 1 or 2 are generally in very good or good condition, 3 is acceptable with the likelihood of some minor remedial actions, whilst grades 4 and 5 require replacement or significant intervention to prevent loss or damage to supplies and quality, these grades being in accordance with the directions given by OFWAT.
The condition grading of assets was initially determined by the survey team prior to a review meeting held after the surveys were complete. At this meeting each site was discussed in detail and minor amendments made where necessary. The site overall condition and performance grading was also determined at this meeting with the final figure weighted for the percentage of assets in each grading.
All sites in the programme were visited at least once with virtually all equipment being inspected. The exception to this was borehole pumping plant where Company records were assessed rather than a visual inspection.
The high number of assets surveyed is reflected in a high confidence grade for the information recorded.
A.5.1. Performance Grade Performance grades were applied to the survey sheets in situations where the assessors were of the opinion that it was possible and practicable to estimate the performance based solely upon the visual inspections. Where this was not possible or practicable the company’s staff and data base were utilised to augment the on-site assessments.
The following performance grading allocations from OFWAT were used:
Grade 1. System robust for planned and unplanned maintenance activity, with no tangible risk of adverse impact on service.
Grade 2. Some increase in operational maintenance activity needed over period to maintain service. Asset malfunctions mitigated by system intervention procedures and/or from alternative assets, with no tangible adverse impact on service.
Grade 3. Asset components requiring refurbishment or renewal on economic grounds alone (such as substantial increase in operational cost to maintain service) and/or to meet health and safety requirements, with no tangible adverse impact on service.
Grade 4. Asset components requiring timely refurbishment or renewal to prevent an imminent reduction in service, which would breach a DG reference standard, statutory quality standard or contributed to overall performance assessment (OPA) score.
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Grade 5a. Asset components requiring refurbishment or renewal which have caused loss of service at local level, within one control zone, breaching a DG reference standard, statutory quality standard or feature in OPA score
Grade 5b. Asset components requiring refurbishment or renewal which have caused loss of service across more than one control zone (control zone definitions company specific to identify different order of risk), a DG reference standard, statutory quality standard or feature in OPA score.
Note: Assets of grade 5a or 5b were graded as 5 only.
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A.5.2. Condition Performance Grade
A.5.2.1. Alre scheme Pump Valves Visible Accumulator Control Panel Notes Pipework Vessel Panel Kiosk
Condition Performa Condition Performa Condition Performa Condition Performa Condition Performa Conditi Performa nce nce nce nce nce on nce Soames I2 Not 3 2 2 2 1 2 2 2 3 2 Farm inspected Gilbert H3 Not Not Not inspected Not fitted 2 2 3 2 Street inspected inspected Ropley G3 Not Not Not inspected Not inspected 2 2 3 2 Soke inspected inspected West End F4 Not Not Not inspected Not inspected 2 2 3 2 Vale inspected inspected
A.5.2.2. Candover Scheme Pump Valves Visible Pipework Accumulator Vessel Control Panel Kiosk Panel Notes Axford 1A Not inspected 3 2 2 2 Not Installed 2 2 2 2 1B Not inspected 3 2 2 2 Not Installed 2 2 2 2 Bradley 2A Not inspected 3 2 2 2 Not Installed 2 2 2 2 2B Not inspected 3 2 2 2 Not Installed 2 2 2 2 Wield 3A Not inspected 3 2 2 2 Not Installed 2 2 2 2 3B Not inspected 3 2 2 2 Not Installed 2 2 2 2
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A.5.3. Site Visit Reports and Photos
A.5.3.1. AXFORD PUMPING STATION SITE VISIT Date of Site Visit 02/06/2011
This site has not run for approx 6 years and was utilised to feed the Candover stream, a tributary of the Itchen.
The site consists of a Transformer compound, a 120 HP Borehole Pump, an 88 HP Borehole Pump, both with Soft Start, flow meter and pressure vessel.
There is a telegraph Pole near the bottom right of the site, which could be utilised for telemetry.
MCC
The bottom entry MCC has been replaced and was manufactured by Barden Control, March 1999.
The main Incomer is 560 Amp Fused and the Soft Starters have 315 Amp Fuses fitted.
The 2900 RPM, 120 HP, 165 Amp FLC borehole and the 88 HP, 120 Amp FLC borehole pumps are normally run in hand mode and are hard wired with no PLC control. There are no power factor correction capacitors fitted.
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SOFT START
Telemechanique Altistart Soft Starts
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DISTRIBUTION BOARD
The Distribution Board has been updated to a 100 Amp consumer unit and feeds the kiosk light, heater, fan and RCD protected socket outlet.
OFWAT Condition Grading: 3
The MCC is in good condition, it will require new door furniture in order to be compliant with MED 4300.
There are Borehole level electrodes installed, which will require testing. The installation of a submersible level transmitter would be required.
Telemetry
Due to no PLC control on site, the Telemetry would require the following:
1. Interposing relays to start and stop pumping 2. The installation of standalone VSDs in the kiosk, in order to control the speed of the pump, as there is not enough space available in the soft start sections of the existing MCC for a VSD. 3. The installation of a Magnetic Flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry.
4. The installation of an ADSL router and Telemetry Outstation. 5. The installation of a submersible level transducer in the borehole in order to provide an analogue signal to telemetry, as there are level probes only existing.
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6. BT contacted to provide the necessary line installation from the existing telegraph pole at site.
NON COMPLIANCE WITH MED 4300
The following points were noted as non compliant with MED 4300:
1. Door locks not triangular type 2. KWh meter not fitted 3. No test facility for starter 4. No portable tools supply fitted 5. No Power Factor Correction Fitted (This would not be required if a VSD was fitted)
Additional Axford photos
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A.5.3.2. BRADLEY PUMPING STATION SITE VISIT Date of Site Visit 02/06/2011
This site has not run for approx 6 years and was utilised to feed the Candover stream, a tributary of the Itchen.
The site consists of a Transformer compound, two 200 HP Borehole Pumps, both with Soft Start, flow meter and pressure vessel.
There is no telegraph Pole near the site, which could be utilised for telemetry.
MCC
The bottom entry MCC has been replaced and was manufactured by Barden Control, March 1999.
The main Incomer is 560 Amp Fused and the Soft Starters have 315 Amp Fuses fitted.
The 2900 RPM, 200 HP, 270 Amp FLC boreholes are normally run in hand mode and are hard wired with no PLC control. There are no power factor correction capacitors fitted.
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SOFT START
Telemechanique Altistart Soft Start
DISTRIBUTION BOARD
The Distribution Board has been updated to a 100 Amp consumer unit and feeds the kiosk light, heater, fan and RCD protected socket outlet.
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OFWAT Condition Grading: 3
The MCC is in good condition, it will require new door furniture in order to be compliant with MED 4300.
There are Borehole level electrodes installed, which will require testing. The installation of a submersible level transmitter would be required.
Telemetry
Due to no PLC control on site, the Telemetry would require the following:
7. Interposing relays to start and stop pumping 8. The installation of standalone VSDs in the kiosk, in order to control the speed of the pump, as there is not enough space available in the soft start sections of the existing MCC for a VSD. 9. The installation of a Magnetic Flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry.
10. The installation of an ADSL router and Telemetry Outstation. 11. The installation of a submersible level transducer in the borehole in order to provide an analogue signal to telemetry, as there are level probes only existing. 12. A satellite communications needs to be installed as there is no BT line near the site.
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NON COMPLIANCE WITH MED 4300
The following points were noted as non compliant with MED 4300:
6. Door locks not triangular type 7. KWh meter not fitted 8. No test facility for starter 9. No portable tools supply fitted 10. No Power Factor Correction Fitted (This would not be required if a VSD was fitted)
Additional Bradley photos
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A.5.3.3. WEILD PUMPING STATION SITE VISIT Date of Site Visit 02/06/2011
This site has not run for approx four years and was utilised to feed the Candover stream, a tributary of the Itchen.
The site consists of a Transformer compound, a 120 HP Borehole Pump, a 200 HP Borehole Pump, both with Soft Start, flow meter and pressure vessel.
There is no telegraph Pole near the site, which could be utilised for telemetry.
The nearest telephone line is at least 500 Mtrs away where there are some houses.
MCC
The bottom entry MCC has been replaced and was manufactured by Barden Control, March 1999.
The main Incomer is 560 Amp Fused and the Soft Starters have 200Amp and 315Amp Fuses fitted.
The 2900 RPM, 120 HP, 165 Amp FLC borehole pump and the 200 HP, 270 Amp FLC borehole pump are normally run in hand mode and are hard wired with no PLC control. There are no power factor correction capacitors fitted.
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SOFT START
Telemechanique Altistart Soft Start
DISTRIBUTION BOARD
The Distribution Board has been updated to a consumer unit and feeds the kiosk light, heater, fan and RCD protected socket outlet.
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OFWAT Condition Grading: 3
The MCC is in good condition, it will require new door furniture in order to be compliant with MED 4300.
There are Borehole level electrodes installed, which will require testing. The installation of a submersible level transmitter would be required.
Telemetry
Due to no PLC control on site, the Telemetry would require the following:
13. Interposing relays to start and stop pumping 14. The installation of standalone VSDs in the kiosk, in order to control the speed of the pump, as there is not enough space available in the soft start sections of the existing MCC for a VSD. 15. The installation of a Magnetic Flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry.
16. The installation of an ADSL router and Telemetry Outstation. 17. The installation of a level transducer in the borehole in order to provide an analogue signal to telemetry, as there are level probes only existing. 18. A satellite communications needs to be installed as there is no BT line near the site.
NON COMPLIANCE WITH MED 4300
The following points were noted as non compliant with MED 4300:
11. Door locks not triangular type 12. KWh meter not fitted 13. No test facility for starter 14. No portable tools supply fitted 15. No Power Factor Correction Fitted (This would not be required if a VSD was fitted)
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Additional Wield photos
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Candover Main Outfall photos
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A.5.3.4. GILBERT STREET PUMPING STATION SITE VISIT Date of Site Visit 02/06/2011
This site has not run for approx four years and was utilised to feed the river Alre.
The site consists of a Transformer compound, a 194 KW Borehole Pump with Soft Start, flow meter and pressure vessel.
There is a telegraph Pole at the entrance of the site, which could be utilised for telemetry.
MCC
The MCC is bottom entry and was manufactured by Barden Control March 1984.
The main Incomer is 630 Amp Fused and the Soft Start has 400Amp Fuses.
The 2900 RPM, 194 KW, 314 Amp FLC borehole is normally run in hand mode and is hard wired with no PLC control. There are no power factor correction capacitors fitted.
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SOFT START
Telemechanique Altistart Soft Start 540mm W X 435mm D X 1350mm H fitted at back of the Borehole Starter Cubicle.
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DISTRIBUTION BOARD
The Distribution Board requires updating to a consumer unit, it feeds the kiosk light, heater, fan and RCD protected socket outlet.
OFWAT Condition Grading: 3
The MCC is in reasonable condition, it could do with a paint touch up, new door furniture and a consumer unit in the distribution section to replace the existing fuses.
There are Borehole level electrodes installed, which will require testing. The installation of a submersible level transmitter would be required.
Telemetry
Due to no PLC control on site, the Telemetry would require the following:
19. Interposing relays to start and stop pumping 20. The installation of a VSD to replace the soft starter in the space available at the back of the existing MCC, in order to control the speed of the pump. 21. The installation of a Magnetic Flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry.
22. The installation of an ADSL router and Telemetry Outstation.
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23. The installation of a submersible level transducer in the borehole in order to provide an analogue signal to telemetry, as there are level probes only existing. 24. BT contacted to provide the necessary line installation from the existing telegraph pole at site.
NON COMPLIANCE WITH MED 4300
The following points were noted as non compliant with MED 4300:
16. Door locks not triangular type 17. KWh meter not fitted 18. No test facility for starter 19. No portable tools supply fitted 20. No Power Factor Correction Fitted (This would not be required if a VSD was fitted)
Additional Gilbert Street photos
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A.5.3.5. ROPLEY SOKE PUMPING STATION SITE VISIT Date of Site Visit 02/06/2011
This site has not run for approx four years and was utilised to feed the river Alre
The site consists of a Transformer compound, a 194 KW Borehole Pump with Soft Start, flow meter and pressure vessel.
There is a telegraph Pole at the access road to the site, approx 150 metres away which could be utilised for telemetry.
MCC
The MCC is bottom entry and was manufactured by Barden Control March 1984.
The main Incomer is 630 Amp Fused and the Soft Start has 400Amp Fuses.
The 2900 RPM, 194 KW, 314 Amp FLC borehole is normally run in hand mode and is hard wired with no PLC control. There are no power factor correction capacitors fitted.
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SOFT START
Telemechanique Altistart Soft Start 540mm W X 435mm D X 1350mm H fitted at back of Starter.
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DISTRIBUTION BOARD
The Distribution Board requires updating to a consumer unit and feeds the kiosk light, heater, fan and RCD protected socket outlet.
OFWAT Condition Grading: 3
The MCC is in reasonable condition, it could do with a paint touch up, new door furniture and a consumer unit in the distribution section to replace the existing fuses.
There are Borehole level electrodes installed, which will require testing. The installation of a submersible level transmitter would be required.
Telemetry
Due to no PLC control on site, the Telemetry would require the following:
25. Interposing relays to start and stop pumping 26. The installation of a VSD to replace the soft starter in the space available at the back of the existing MCC, in order to control the speed of the pump. 27. The installation of a Magnetic Flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry.
28. The installation of an ADSL router and Telemetry Outstation.
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29. The installation of a submersible level transducer in the borehole in order to provide an analogue signal to telemetry, as there are level probes only existing. 30. BT contacted to provide the necessary line installation from the existing telegraph pole near the site. Alternatively a satellite communications could be installed.
NON COMPLIANCE WITH MED 4300
The following points were noted as non compliant with MED 4300:
21. Door locks not triangular type 22. KWh meter not fitted 23. No test facility for starter 24. No portable tools supply fitted 25. No Power Factor Correction Fitted (This would not be required if a VSD was fitted)
Additional Ropley Soke photos
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A.5.3.6. SOAMES FARM PUMPING STATION SITE VISIT Date of Site Visit 02/06/2011
This site has not run for approx four years and was utilised to feed the Alre stream, a tributary of the Itchen.
The site consists of a Transformer compound, a 190 KW Borehole Pump with Soft Start, flow meter and pressure vessel.
There is a telegraph Pole at the bottom right of the site, which could be utilised for telemetry purposes.
MCC
The MCC is bottom entry and was manufactured by Barden Control March 1984.
The main Incomer is 630 Amp Fused and the Soft Start has 400Amp Fuses.
The 2900 RPM, 190 KW, 348 Amp FLC borehole is normally run in hand mode and is hard wired with no PLC control. There are no power factor correction capacitors fitted.
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SOFT START
Telemechanique Altistart Soft Start 400mm W X 350mm D X 950mm H
DISTRIBUTION BOARD
The Distribution Board requires updating to a consumer unit, it feeds the kiosk light, heater, fan and RCD protected socket outlet.
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OFWAT Condition Grading: 3
The MCC is in reasonable condition, it could do with a paint touch up, new door furniture and a consumer unit in the distribution section to replace the existing fuses.
There are Borehole level electrodes installed, which will require testing. The installation of a submersible level transmitter would be required.
Telemetry
Due to no PLC control on site, the Telemetry would require the following:
31. Interposing relays to start and stop pumping 32. The installation of a standalone VSD in the kiosk, in order to control the speed of the pump, as there is not enough space available in the soft start section of the existing MCC for a VSD. 33. The installation of a Magnetic Flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry.
34. The installation of an ADSL router and Telemetry Outstation. 35. The installation of a level transducer in the borehole in order to provide an analogue signal to telemetry, as there are level probes only existing. 36. BT contacted to provide the necessary line installation from the existing telegraph pole at site.
NON COMPLIANCE WITH MED 4300
The following points were noted as non compliant with MED 4300:
26. Door locks not triangular type 27. KWh meter not fitted 28. No test facility for starter 29. No portable tools supply fitted 30. No Power Factor Correction Fitted (This would not be required if a VSD was fitted)
Additional Soames Farm photos
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A.5.3.7. WEST END VALE PUMPING STATION SITE VISIT Date of Site Visit 02/06/2011
This site has not run for approx four years and was utilised to feed the river Alre.
The site consists of a Transformer compound, a 170 KW Borehole Pump with Soft Start, flow meter and pressure vessel.
There is no telegraph Pole near the site, which could be utilised for telemetry.
The nearest telephone line is at least 500 Mtrs away where there are some houses.
MCC AND SOFT START
The MCC is bottom entry and was manufactured by Barden Control March 1984.
The main Incomer is 630 Amp Fused and the Soft Start has 400Amp Fuses.
The 2900 RPM, 170 KW, 311 Amp FLC borehole is normally run in hand mode and is hard wired with no PLC control. There are no power factor correction capacitors fitted.
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DISTRIBUTION BOARD
The Distribution Board requires updating to a consumer unit, it feeds the kiosk light, heater, fan and RCD protected socket outlet.
OFWAT Condition Grading: 3
The MCC is in reasonable condition, it could do with a paint touch up, new door furniture and a consumer unit in the distribution section to replace the existing fuses.
There are Borehole level electrodes installed, which will require testing. The installation of a submersible level transmitter would be required.
Telemetry
Due to no PLC control on site, the Telemetry would require the following:
37. Interposing relays to start and stop pumping
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38. The installation of a standalone VSD in the kiosk, in order to control the speed of the pump, as there is not enough space available in the soft start section of the existing MCC for a VSD. 39. The installation of a Magnetic Flow meter to replace the Kent Helix meter installed, in order to provide an analogue signal to telemetry.
40. The installation of an ADSL router and Telemetry Outstation. 41. The installation of a level transducer in the borehole in order to provide an analogue signal to telemetry, as there are level probes only existing. 42. A satellite communications needs to be installed as there is no BT line near the site. NON COMPLIANCE WITH MED 4300
The following points were noted as non compliant with MED 4300:
31. Door locks not triangular type 32. KWh meter not fitted 33. No test facility for starter 34. No portable tools supply fitted 35. No Power Factor Correction Fitted (This would not be required if a VSD was fitted)
Additional West End Vale photos
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Additional Alre scheme photos
Alre Main Outfall
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Alre Cress Beds photos
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Appendix B. Water Quality Data
B.1. Pre-test water quality testing and results
B.1.1. Overview This short review assesses water samples collected by the Environment Agency and compares groundwater and surface water samples. It provides an assessment of the likely impact on the river water quality of discharging water of the type and quality indicated by the groundwater samples.
B.1.2. Summary of samples Water samples have been collected by the Environment Agency to assess water quality from boreholes on the Candover and Alre augmentation schemes and the River Alre at the outfall for the Drayton pipeline and in the receiving waters. In addition historical data for the borehole at Axford on the Candover scheme as well as routine sample results for June and July 2011 for the River Candover at Borough Bridge and the River Alre at Drove Lane as well as Abbotstone for comparison have been made available. Table 1 summarises the samples considered in this review.
Table 1
Sample name Location & Dates Sample type Comments Grid Ref Axford 1A Axford site 06/07/2011 Groundwater Unfiltered SU 61049 sample 43045 Bradley 2B Bradley site 06/07/2011 Groundwater Unfiltered SU62634 41969 sample Wield 3A Wield Site 06/07/2011 Groundwater Unfiltered SU 61549 sample 40547 Ropley Soke Ropley Soke 18/07/2011 Groundwater Unfiltered SU 65299 sample 33998 West End Vale West End Vale 04/07/2011 Groundwater Unfiltered SU6367 3606 sample Gilbert Street Gilbert Street 27/07/2011 Groundwater Unfiltered SU 65444 sample 32603 Soames Farm Soames Farm 03/08/2011 Groundwater Unfiltered SU 6450 3050 sample Candover Borough Bridge 01/06/2011 River water Routine sample 05/07/2011 Alre Drove Lane 06/06/2011 River water Routine sample 05/07/2011 Abbotstone SU 56371 01/06/2011 River water 34559 28/06/2011 05/07/2011 Watercourse at Drayton 27/07/2011 Drayton Drayton pipeline Drayton SU 27/07/2011 Groundwater West End Vale 59690 33312 running
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Axford Axford site 2008 - 2009 Groundwater SU 61049 43045
B.1.3. Sampling methodology Sampling was undertaken by Environment Agency staff, either as part of routine sample rounds (for samples at Borough Bridge, Drove Lane and Abbotstone), as part of the refurbishment of the Alre augmentation scheme (West End Vale, Ropley Soke, Gilbert Street and Soames Farm) and as a pre- test check on the Candover augmentation scheme (for Axford, Bradley and Wield). It is understood that samples from the augmentation schemes were collected as unfiltered samples and that the boreholes were run until three borehole volumes of water had been discharged prior to the sample being collected. This was in order to collect a sample representative of groundwater rather than water that had been standing in the borehole. Some historical data from Axford was made available however there are concerns over the collection method and it is thought unlikely that the boreholes were purged prior to sample collection. As a consequence results from that dataset have not been considered in detail as part of this assessment.
B.1.4. Water types Major Ion analysis indicates Calcium Bicarbonate type waters for both groundwater and the surface water course at Drayton. These samples are all typical chalk waters. This is unsurprising given the down hydraulic gradient location of the Drayton Stream. The Piper diagram in Figure Appendix B.1 provides a plot showing the ionic relationship between the samples collected and analysed for major ions (this does not include the samples at Borough Bridge, Drove Lane or Abbotstone. It is expected that these surface waters would also show the same major ion hydrochemistry given the local chalk geology and hydraulic gradient).
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Figure Appendix B.1 Ca + Mg 100% SO Piper Plot of Hydrochemistry of Itchen Augmentation Scheme: 4 + Cl 100% abstraction boreholes and receiving water for Alre branch at Drayton
Ropley Soke
West End Vale
Gilbert Street
Soames Farm
West End Vale-Drayton HCO 3 100% Na 100% West End Vale - Drayton
Drayton stream
Axf 1A
Mg 100% 4 100% SO Brad 2B
Wield 3A
Na 100%
HCO3100%
100% Ca 100% HCO3 Na 100% Cl 100%
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B.1.5. Consideration of water quality To review the quality of the water in the groundwater and river water samples a number of water quality regulations have been considered. These are the EU Drinking Water Directive (DWD), the Freshwater Fish Directive (FWFD), for both Cyprinids and Salmonids and requirements under the Water Framework Directive (WFD). It is difficult to make comparisons against Directive limits or guidelines as they are mainly intended to be an annual target so non compliance from a single sample does not necessarily indicate a failure to comply with the Directive.
The set of results from surface and groundwater have been reviewed and the following parameter groups are discussed here for assessment of the suitability of discharging groundwater into the surface water environment:
Metals Nutrients Pesticides PAH’s
It should be remembered that due to the hydraulic gradient the groundwater would be expected to discharge into the surface water system under natural conditions.
B.1.5.1. Metals Zinc: WFD suggests 75 ug/L at observed hardness, FWFD limits are higher at 300 ug/L salmonid and 1000ug/L Cyprinid at hardness observed. There is a non compliant result at Gilbert Street (87.5 ug/L) for WFD.
Aluminium: DWD limits are 200 ug/L. There is a non-compliant result at West End Vale 270 ug/L on 12/7/2011, however the sample collected on 27/07/2011 is compliant.
Copper: DWD 2000 ug/L; FWFD 10ug/L salmonid; there is a non-compliant result at Gilbert Street (26.5 ug/L) and Wield 3A (11.5 ug/L).
Lead: WFD 7.2 ug/L. There is a non compliant result at Gilbert Street (43.1 ug/L).
Summary
There appear to be slightly elevated metals concentrations (different exceedences of Directives for different metals) at Gilbert Street and Wield 3A. An exceedence at West End Vale was not repeated following a second sample collection. Given that the other sources in the augmentation schemes do not demonstrate similar exceedences then the concentrations would be expected to be adequately diluted by other abstractions and the receiving waters.
B.1.5.2. Nutrients Nitrite: (analysed as N, so needs to be converted for comparison NO2 = Nx3.3) FWFD Guideline Salmonids 0.01 mg/L and Cyprinids 0.03 mg/L as NO2. Spot results for all surface waters are non-compliant with FWFD nitrite as N concentrations for Salmonids and Cyprinids however, these are single sample results and comparison with FWFD should be considered over 12 months. Addition of groundwater from the augmentations schemes, which is compliant with the FWFD limits, would be beneficial in diluting these concentrations.
Ammoniacal nitrogen: as N (FWFD Imperative 0.025 mg/L; Guideline 0.005 mg/L) – Drove Lane is non compliant on 06/06/11 (0.54 mg/L). All other sample results show concentrations of < 0.03 mg/L which at the Imperative (allowing for rounding).
Summary
There doesn’t appear to be a problem with nutrient concentrations for the groundwater results considered here. The addition of groundwater would be expected to dilute nutrient concentrations in the surface water system.
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B.1.5.3. Pesticides No recent sampling was undertaken for pesticides, however historical sampling at Axford did not indicate any elevated concentrations or exceedences for the pesticides and herbicides analysed for.
Summary
Not of concern
B.1.5.4. Polyaromatic Hydrocarbons (PAH) These are limited by the DWD to 0.01 ug/L for any one compound or 0.1 ug/L for the sum of four: benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene and indeno(123-cd)pyrene. Recent groundwater samples from the Candover scheme indicate concentrations of more than 0.01 ug/L for some PAH compounds. It is thought this may be attributable to the method of sealing the pipeline that would have been used at the time of construction.
Summary
Some exceedences of the DWD PAH concentrations have been found for the Candover scheme. It is thought these are likely to be due to the pipeline construction method.
B.1.6. Conclusions Occasional exceedences of parameter limits occurred in the samples considered here. These were mainly for metals for groundwater samples and nutrients for surface water samples. The Candover scheme samples show non-compliance with DWD PAH concentrations and it is thought this may be attributable to the method of sealing pipeline joints that would have been in general use at the time of construction. It is considered likely that slightly elevated concentration of these compounds has resulted partly due lack of regular use of the scheme. It is therefore considered likely that the compound concentrations will reduce if the scheme is used and the pipeline is adequately flushed with clean groundwater.
B.1.7. Recommendations It is recommended that the schemes are pumped for a prolonged period and abstracted water is monitored at each abstraction borehole and at the end of each pipeline. Samples should be collected after approximately a week of pumping (a week from the start for each abstraction borehole) and again at approximately weekly intervals.
Boreholes should be started such that Soames Farm starts first on the Bishops Sutton pipeline to dilute Gilbert Street.
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Itchen Implementation NEP Scheme Appendix C. Stakeholder Engagement
C.1. Webpage
River Itchen augmentation scheme
Water quality in the River Itchen is naturally high because it is fed by springs which are filtered through the chalk. Find out more about our scheme to reduce abstraction and increase the amount of water flowing in the river.
About the River Itchen
The River Itchen is one of the finest chalk streams in the world. It rises on the upper chalk of Cheriton near Winchester and flows for 28 miles to Southampton Water. The river provides high quality habitats for wildlife and is home to a wide range of protected species including otter and Southern Damselfly. It is a Site of Special Scientific Interest (SSSI) and a Special Area of Conservation (SAC).
Water abstraction in the Itchen catchment
There are many water abstractions from the River Itchen for public water supply. The main water intake is at Otterbourne to supply water to southern Hampshire (operated by Southern Water Services Ltd). There are smaller abstractions at Totford, Easton and Twyford.
Overall, the biggest abstraction pressures on the Itchen are in its lower reaches for public water supply to the wider Southampton urban area. This water is finally discharged into the sea from coastal sewage works.
We regularly assess the impact of abstractions on river flow so that we know how much water, if any, is available for abstraction licensing. There are large abstractions for watercress and fish farming, and a few small hydropower schemes. All of these uses return water back to the environment very close to where it is abstracted. Local sewage treatment works and septic tanks also return almost all of the water they use to the catchment.
Balancing the needs of people and the environment
Under the Water Resources Act 1991, the Environment Agency has a duty to ensure water resources are managed and conserved to meet the needs of people and the environment.
We are working with abstraction licence holders to make sure that the amount of water taken from the River Itchen or from the chalk can be sustained without damaging the environment.
Portsmouth Water have recently applied to reduce their licence near Southampton and Southern Water are also working with us to modify their licences.
The River Itchen augmentation scheme
We are starting to shut down our test of the Itchen Augmentation schemes in the week commencing 24th October 2011. Our use of the Alre and Candover Schemes has increased flows in the River Alre, Candover Stream and River Itchen since we turned the schemes on in mid-September. As the weather over the last few weeks has been dry, river flows in the upper Itchen remain low so we will continue to put a small amount of water into the Candover Stream and
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River Alre at Bishops Sutton until flow in these rivers starts to naturally recover as a result of autumn rain.
The test has provided us with valuable information about how we could manage and use these augmentation schemes in the future. Over the coming weeks, we need to work with others to analyse the data we have collected to assess how use of the schemes has affected river flows, groundwater levels, water quality and the sensitive species that live in the upper Itchen.
© Environment Agency 2012 | Privacy and cookies | Terms and conditions
Author: The Environment Agency | [email protected]
Last updated: 21 April 2012
http://www.environment-agency.gov.uk/business/topics/water/132410.aspx copied from website 23/04/2012
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Itchen Implementation NEP Scheme C.2. Frequently asked Questions
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Itchen Implementation NEP Scheme C.3. Press Release (Draft)
DRAFT, ** August 2011
Partnership scheme means no low flows on the River Itchen this summer
The Environment Agency is working with two water companies on a pilot project to ensure that water supplies for people and the environment are further protected on the River Itchen this summer. In partnership with Portsmouth Water and Southern Water, the Environment Agency is investigating ways to manage water resources more effectively in south Hampshire over the coming years. Following the driest spring on record this year, levels on the Itchen are lower than usual and during the summer months demand for water is high. The Itchen is of international importance for wildlife as well as being a critical water resource for central and southern Hampshire. There are two schemes on the Candover Stream and the River Alre that the Environment Agency operates to pump more water into the Itchen when flows become low. The pumping systems have been used on occasions since 1990 but they will be in full flow from early September to mid-October this year to test how much water they can pump into the river and how the local environment responds. During operation, the schemes take (or abstract) water from the chalk aquifer of the Hampshire Downs and discharge it through pipelines into the headwaters of the Candover Stream and River Alre. The water flows down these rivers into the main River Itchen to support river flow and water quality.
Rod Murchie of the Environment Agency said: “Flows and groundwater levels this year in the River Itchen valley and its headwaters are low following a very dry spring, so it is an ideal opportunity to test the effectiveness of the schemes.
“The result of the pumping will be to keep flows in the Candover Stream, River Alre and River Itchen slightly higher than would be expected for this year. This work will ensure that there is a plentiful supply of water for both people and the environment, but will it not increase the risk of flooding to the area.
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“Working with Southern Water, we will be monitoring groundwater levels and river flows throughout the River Itchen and its tributaries. With Hampshire & Isle of Wight Wildlife Trust we will monitor the impact of the schemes on sensitive wildlife species in the Candover Stream and River Alre.
“Water is a precious resource in Hampshire. By 2050 climate change could reduce the amount of water available in the environment by 15 per cent. On average each resident in the county uses 168 litres of water per day, and so everyone needs to reduce this amount to avoid long term detrimental impacts on our environment.”
Further information about the River Itchen Augmentation scheme is available on our website at: www**********************************************************
ENDS
All media enquiries: 0118 953 5555 Please ask for the duty press officer Environment Agency news releases, both national and regional, can be found on its web site: www.environment-agency.gov.uk
Notes to Editors The Candover scheme was the first of the two schemes to be constructed and it was extensively tested during the 1976 drought to see how effective it was and to understand the possible impacts on other water abstractors and the environment. This proved to be a success and so the Alre scheme was constructed and then tested in 1989.
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Itchen Implementation NEP Scheme C.4. Media Coverage
C.4.1. Hampshire Chronicle Environment Agency launches scheme to boost River Itchen water levels
10:00am Thursday 22nd September 2011 in Winchester
Rod Murchie of the Environment Agency at the Candover Stream where water is being pumped into the River Itchen
ENVIRONMENT chiefs have begun pumping more water into the River Itchen in an attempt to protect against droughts.
Pumps were switched on at Candover Stream, north of Alresford, on Monday (Sept 19) as part of an Environment
Agency scheme to boost water levels downstream.
The agency is pumping this water to discover whether it would provide a solution in prolonged dry weather.
Rod Murchie, of the agency, said: “We are working with Southern Water to see if our scheme is part of their solution into providing people with water during times of drought.
He added: “Companies like Southern Water take water out of the Itchen and supply it to people and the Environment
Agency licences them to do this.
“But the River Itchen has been recently identified as of crucial importance to wildlife and a special area of conservation. It is now of national and international importance and so it means we will reduce our licences to companies during times of drought so they take less water and do not disturb the ecological system.
“We are not going to shut people off but we will have to reduce the amount of water for Southern Water to supply.
This scheme may boost the levels and help them out.”
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The scheme was supposed to start on September 8 but was postponed after concerns were raised over threats to a rare native crayfish that is only found in the Candover and Arle valleys, both where the agency has these pumps.
But Mr Murchie said that although there was a risk of causing stress to the crayfish and their environment, it was believed the scheme would not harm them.
He said: “We have decided now that the risk is acceptable after a lot of argument and analysis of samples in our labs.”
The pumps have been used several times before in the past three decades during droughts and will remain working for the next six weeks to discover whether they are a viable solution.
Hampshire Chronicle http://www.hampshirechronicle.co.uk/news/winchester/9264199.Environment_Agency_launches_scheme_to_boost_Ri ver_Itchen_water_levels/ downloaded 13/05/2012
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C.4.2. Southern Daily Echo
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Itchen Implementation NEP Scheme Appendix D. Pipeline modelling
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D.1. Tables for WANDA
D.1.1. Pipelines Chainage Elevation Diameter Fittings in section Friction loss Comments Assume roughness coefficient 0.15mm for all pipe A Pump Axford 1A 0 69 200 90 bend, NRV, 2 x 3.34 Gate valve, in-line tee, Helix FM Confluence with 67 106.52 200 Axford 1B
B Pump Axford 1B 0 69 200 90 bend, NRV, 2 x 3.79 Gate valve, tee to branch, Helix FM Confluence with 47 106.52 200 Axford 1A
C Confluence of Axford 0 106.52 250 Gate valve, 5 x in-line 2.67 valve 1A & 1B tee, tee to branch. 10 106.56 250 15 106.89 250 74 107.03 250 75 107.31 250 205 105.23 250 330 104.7 250 342 104.52 250 344 104.87 250 389 104.6 250 470 104.26 250 wash out 471 103.8 250 472 103.91 250
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Chainage Elevation Diameter Fittings in section Friction loss Comments Assume roughness coefficient 0.15mm for all pipe 610 110.68 250 700 114.02 250 755 112.17 250 air vent 835 107.47 250 930 106.26 250 954 105.81 250 initial on wash out 1044 105.4 250 1223 112.55 250 air vent 1388 109.1 250 1493 103.94 250 1554 103.91 250 wash out 1739 107.51 250 Confluence with 1754 107.51 250 Bradley borehole main
D Pump Bradley 2A 0 61 200 90 bend, NRV, 2 x 3.34 Gate valve, in-line tee, Helix FM Confluence with 80 116.9 200 Bradley 2B
E Pump Bradley 2B 0 64 200 90 bend, NRV, 2 x 3.34 Gate valve, tee to branch, Helix FM Confluence with 62 116.9 200 Bradley 2A
F Confluence of 0 116.9 250 Gate valve, 2 x in-line 0.82 valve Bradley 2A & 2B tee
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Chainage Elevation Diameter Fittings in section Friction loss Comments Assume roughness coefficient 0.15mm for all pipe 50 119.07 250 200 117.22 250 340 122.26 250 580 124.56 250 676 124.58 250 air vent 776 124.38 250 1196 108.1 250 Confluence with 1466 107.51 250 Bradley Axford main
G Confluence of Axford 0 107.51 350 In-line tee 0.35 and Bradley boreholes 415 117.82 350 Confluence with 420 117.91 350 Wield borehole main
H Pump Wield 3A 0 62 200 90 bend, NRV, 2 x 3.34 Gate valve, in-line tee, Helix FM Confluence with 69 114.37 200 Wield 3B
I Pump Wield 3B 0 61 200 90 bend, NRV, 2 x 3.79 Gate valve, tee to branch, Helix FM Confluence with 60 114.37 200 Wield 3A
J
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Chainage Elevation Diameter Fittings in section Friction loss Comments Assume roughness coefficient 0.15mm for all pipe Confluence of Wield 0 114.37 250 2 x gate valve, tee to 1.04 valve 3A & 3B branch 5 114.61 250 valve 85 115.78 250 215 115.53 250 233 116.49 250 meter in housing 438 116.54 250 538 114.35 250 628 114.31 250 Confluence with main 769 117.91 250 pipeline
K Confluence with 0 117.91 450 Gate valve, 6 x in-line 2.22 Wield boreholes main tee 163 121.88 450 air vent 295 117.97 450 315 116.81 450 385 113.26 450 460 110.16 450 535 108.44 450 580 108.18 450 589 107.79 450 double wash out/air valve? 669 107.32 450 914 106.59 450 1124 106.85 450 1322 107.81 450 air vent 1437 105.66 450 1502 103.76 450 1533 102.24 450 1573 100.1 450 1753 96.2 450
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Chainage Elevation Diameter Fittings in section Friction loss Comments Assume roughness coefficient 0.15mm for all pipe 1853 97.5 450 1937 97.84 450 wash out 1950 96.6 450 1952 96.88 450 2292 112.34 450 2382 114.75 450 2452 115.63 450 2542 117.02 450 2545 117 450 air valve? 2675 116.84 450 2709 116.12 450 3009 101.42 450 3049 100.38 450 3294 106.8 450 3329 107.88 450 3447 112.55 450 3477 113.62 450 3692 116.59 450 3902 112.6 450 3907 112.85 450 3992 109.59 450 4182 111.11 450 4382 110.57 450 4522 104.75 450 4687 101.85 450 air vent 4702 100.87 450 4917 100.19 450 4922 100.36 450 5289 88.59 450 Tee off to minor 5314 87.83 450 outfall
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Chainage Elevation Diameter Fittings in section Friction loss Comments Assume roughness coefficient 0.15mm for all pipe
M Tee off to minor 0 87.83 450 Gate valve, exit loss 1.12 outfall 184 87.72 450 199 85.97 450 200 85.99 450 287 78.43 450 292 78.29 450 432 77.05 450 442 76.83 450 637 77.02 450 652 76.21 450 653 76.23 450 654 76.92 450 659 77.2 450 679 77.97 450 791 77.8 450 891 77.97 450 946 74.69 450 valve Major outfall 949 74.96 450 concrete wall
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D.1.2. Pump Characteristics Bradley 2A,2B & Wield 3A (150kW) Q(m^3/hr) Q(l/s) H(m) efficiency overall (%) 225 63 146 63 250 69 139 64
275 76 131 65 300 83 125 67
325 90 119 67 350 97 113 68 375 104 107 68 400 111 99 67 425 118 85 64 450 125 45 60
Axford 1A &1B (50kW) Q(m^3/hr) Q(l/s) H(m) efficiency overall (%) 108 30 90 47 144 40 80 56 180 50 76 62 216 60 73 67 252 70 66 68 288 80 58 67 324 90 47 63
360 100 26 44
Wield 3B (66kW) Q(m^3/hr) Q(l/s) H(m) efficiency overall (%) 108 30 130 46 144 40 106 55 180 50 102 61 216 60 97 65 252 70 89 67 288 80 77 67 324 90 62 62 360 100 37 44
D.1.3. Valves Name Ref Valve_Type Easting Northing Source Datum Minor Outfall Valve 456964 137540 Atkins 87.45 19/02/96 Major Outfall Valve 456816 136763 Atkins 74.69 19/02/96 Air Vent MP AV 06 Air Vent 457468 137881 Atkins 101.85 1 19/02/96 Chilton MP V 05 Valve 459134 139186 Atkins 117 Candover 19/02/96 The Avenue MP WO 04 Wash Out 459626 139543 Atkins 96.6 19/02/96 MP AV 03 Air Vent 460004 140028 Atkins 107.81 1 19/02/96 Preston Grange MP DAV 02 Double Air 460592 140624 Atkins 107.79 Valve 19/02/96 MP AV 01 Air Vent 460857 140929 Atkins 121.88 1 19/02/96 Wield Valve 461510 140492 Atkins 116.9 19/02/96 Fairview Farm AX WO 05 Wash Out 461277 141466 Atkins 103.91 19/02/96
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Name Ref Valve_Type Easting Northing Source Datum AX AV 04 Air Vent 461231 141794 Atkins 112.55 1 19/02/96 Bradley Corner BRAD AV Air Vent 462060 141549 Atkins 124.58 1 01 19/02/96 Bradley Corner Valve 462569 141938 Atkins 114.61 19/02/96 AX WO 03 Wash Out 461247 142062 Atkins 105.81 19/02/96 East Park AX AV 02 Air Vent 461189 142253 Atkins 112.17 1 19/02/96 Allway, Axford AX WO 01 Wash Out 461042 142497 Atkins 104.26 19/02/96 Axford Valve 461068 142963 Atkins 106.52 19/02/96
D.1.4. Borehole Water Levels mAOD Axford 1A 86.3 Axford 1B 79.09 Bradley 2A 88.42 Bradley 2B 88.11 Wield 3A 87.34 Wield 3B 90.92
D.1.5. Scenarios
Scenario ML/d l/s 1 Axford 1A 5.2 60 Axford 1B 5.2 60 Bradley 9 104 2A Bradley 9 104 2B Wield 3A 6.2 72 Wield 3B 9 104
Scenario 2 Axford 1A 3.5 41 Axford 1B 3.2 37 Bradley 9.2 106 2A Bradley 9.9 115 2B Wield 3A 10 116 Wield 3B 6 69
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D.1.6. K-factors MW Standard K-Factors
Type of fitting K l/d Type of fitting K l/d appr approx ox. . Entry losses Sudden enlargements Sharp edged 0.5 22 (K & I/D for entrance smaller dia.) Re-entrant 0.8 36 Inlet dia:outlet entrance Slightly rounded 0.25 11 5:4 0.15 7 entrance Bellmouth 0.05 2 3:4 0.2 9 entrance Foot valve and 2.5 113 2:3 0.35 16 strainer Intermediate 1:2 0.6 27 losses Elbows (R/D = 1/3 1:3 0.8 36 approx. 22.5 o 0.2 9 1:5 or 1 45 over 45o 0.4 18 Sudden contractions 90o 1 45 (K & I/D for smaller dia.) 90o 1.25 56 Inlet dia:outlet Plastic Short rad. bends 5:4 0.15 7 (R/D = 1) 22.5 o 0.15 7 4:3 0.2 9 45o 0.3 14 3:2 0.3 14 90o 0.75 34 2:1 0.35 16 Long rad.bends (R/D = 2 - 3:1 0.45 20 7) 22.5 o 0.1 5 5 & over 0.5 22 :1 45o 0.2 9 B.S.Tap ers 90o 0.4 18 (K & i/D for smaller dia.) Sweeps (R/D = 8 - Flow to small end neg. neg. 50) 22.5 o 0.05 2 Flow to large end 45o 0.1 5 Outlet dia : Inlet 90o 0.2 9 5:4 0.03 1.5 (1.25) Mitre elbows 4:3 0.04 2 (1.33) 22.5 o - 0.15 7 3:2 (1.5) 0.07 3.5 2 piece 30o - 2 0.2 9 2:1 (2) 0.12 6 piece 45o - 2 or 3 piece 0.3 14 Valves 60o - 2 0.65 29 Gate valves: Fully 0.12 5 piece open 60o - 3 0.25 11 1/4 1 45 piece closed 90o - 2 1.25 56 1/2 6 270 piece closed 90o - 3 0.5 22 3/4 24 1080 piece closed 90o - 4 0.3 14 Globe valves 10 450
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piece Tees R.angle valves 5 225 Flow in 0.35 16 Reflux valves 1 45 line Line to branch or Butterfly valves 0.3 14 v.v. sharp 1.2 54 Exit edged losses radius 0.8 36 Sudden 1 45 ed enlargement Angle Bellmouth outlet 0.2 9 branche s Flow in 0.35 16 Meters line Line to branch or Ventu v.v. ri: 30o 0.4 18 Mercurial type up to 30% 45o 0.6 27 up to Water 20% type 90o 0.8 36 up to Orifice 67%
Roughness Exampl Factors es k Good Normal Poor 0.003 mm Pitch-fibre pipes running Smooth drawn non-ferrous full bore pipes of Al, Brass, Cu, Pb, plastics 0.015 mm Uncoate Asbestos cement d Steel 0.03 mm Wrought iron, Spun Bitumen lined metal Coated Steel pipes Spun Concrete lined metal pipes Uncoated Steel Pitch-fibre pipes running part full 0.06 mm Galvanised Iron, Coated Wrought Iron, Coated Steel Uncoated Cats Iron Steel Concrete Class 4, Glazed vitrified clay 0.15 mm Rusty wrought iron, Galv.iron, coated C.I., Uncoated C.I. Concrete Cl.4 Tate relined pipes 0.3 mm Wood stave pipes, planed plank Uncoated C.I., Glazed vitrified flumes, clay, Monolithic construction dia.600 mm and over in 1m against steel units, or forms, spun precast pipes, dia. 300 mm and over in 0.6 smooth m units trowelled surfaces 0.6 mm Riveted steel pipes, Water Mains Rusty wrought iron, smooth slightly trowelled attacked by turberculation (up to 20 surfaces yrs. use) Glazed brickwork, mature foul sewer - slimed to no more than 6 mm 1.5 mm Riveted steel - up to 20 yrs Riveted steel pipes use. unturbercolated Water main moderately Water main slightly attacked by Pre-cast attacked by tubercolation pipes, tubercolation, well pointed (40-50 yrs use), glazed brickwork,
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brick work mature foul sewer slimed to not more than 6 mm 3 mm Riveted steel, untubercolated, over 6 mm (full rivets, Water main moderately attacked by tubercolation (40- 50 yrs) 6 mm Water mains appreciably attacked by tubercolation, up to 20 yrs use, Mature fouls sewers - < 25 mm slime 15 mm Water mains severely Water mains appreciably attacked by attacked by tubercolation, up to 20 yrs tubercolation, up to 20 yrs use, Straight use, Mature uniform earth fouls sewers - < 25 mm slime channels
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D.2. Hydraulic Profile Scenario 1.BMP
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Itchen Implementation NEP Scheme D.3. Hydraulic Profile Scenario 2.BMP
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Itchen Implementation NEP Scheme D.4. Hydraulic Profile Scenario 3.BMP
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Itchen Implementation NEP Scheme D.5. Candover Schematic.pdf
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Itchen Implementation NEP Scheme Appendix E. Ecological Reporting
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River Itchen SSSI / SAC Flow Augmentation Schemes
Investigating the potential ecological implications of the Upper Itchen flow augmentation schemes: a specific focus on the resident white-clawed crayfish (Austropotamobius pallipes) population.
August 2012
Dr. Ben Rushbrook Southern Chalkstreams Project Officer, Hampshire and Isle of Wight Wildlife Trust Thomas Selby Research Assistant, Hampshire and Isle of Wight Wildlife Trust
Dr. Kerry Evans CEnv MIEEEM Environmental Monitoring Officer (Analysis & Reporting), Environment Agency
Augmentation schemes: ecological and anomalous behaviour report
Front Cover: View of a large white-clawed crayfish encountered during crayfish behavioural monitoring
Information contained in this report is intended for the Environment Agency and Southern Water Services Limited. Species records of rare and notable species may be forwarded to relevant recording organisations with site names removed. All other information in this report should not be passed on to any third party without the express permission of Environment Agency, Southern Water Services Limited and the Hampshire and Isle of Wight Wildlife Trust.
This document should be cited as: Rushbrook, B.J., Selby, T. & Evans, K. (2012). Investigating the potential ecological implications of the Upper Itchen flow augmentation schemes: a specific focus on the resident white-clawed crayfish (Austropotamobius pallipes) population. A report prepared for the Environment Agency and Southern Water Services Limited. Hampshire and Isle of Wight Wildlife Trust.
Rushbrook et al Hampshire & Isle of Wight Wildlife Trust /Environment Agency
Augmentation schemes: ecological and anomalous behaviour report i
Contents
Executive Summary iii
Acknowledgements vi
1. Introduction 1 1.1. Background 1 1.2. Proposals 1 1.3. Remit 1
2. Ecological Considerations 3 2.1. White-clawed crayfish 3 2.2. Macroinvertebrates 4 2.3. Water quality 5
3. Aims and Objectives 7
4. Augmentation Scenarios 8 4.1. Upper Itchen flow augmentation schemes 8 4.2. Proposed operation of flow augmentation schemes 9 4.3. Operation of flow augmentation schemes 9
5. Ecological Monitoring 11 5.1. Methodology 11 5.1.1. Drift 11 5.1.2. Physico-chemical 15 5.1.3. Water quality 16 5.1.4. Statistical analysis 16 5.2. Results 20 5.2.1. Drift and associated abiotic factors 20 5.2.2. Invertebrate community depletion at Abbotstone Causeway 26 5.2.3. Physico-chemical 27 5.2.4. Water quality 29 5.3. Discussion 30 5.3.1. Flow augmentation, water levels and flow rates 30 5.3.2. Flow augmentation and white-clawed crayfish 32 5.3.3. Flow augmentation and invertebrate drift 36 5.3.4. Flow augmentation and invertebrate community depletion 37 5.3.5. Flow augmentation and water quality 38
6. Anomalous Crayfish Behaviour 40 6.1. Background 40 6.2. Methodology – Candover Stream 42 6.2.1. Manual searches 42
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6.2.2. Statistical analysis 45 6.3. Methodology – River Alre 45 6.3.1. Manual searches 46 6.3.2. Statistical analysis 47 6.4. Results – Candover Stream 47 6.4.1. Upper Fobdown 47 6.4.2. Lower Fobdown 54 6.5. Results – River Alre 54 6.6. Discussion 55 6.6.1. Effects of the Upper Itchen flow augmentation schemes 55 6.6.2. Consequences and potential causes of the anomalous behaviour 55 6.6.3. Lower Fobdown and the ‘absence’ of anomalous behaviour 60
7. Conclusions and Recommendations 61 7.1. Summary 61 7.1.1. Ecological monitoring 61 7.1.2. Anomalous crayfish behaviour monitoring 62 7.2. Ecological cost-benefit analysis of Upper Itchen flow augmentation 62 7.3. Future operation of the Candover Stream scheme 64 7.3.1. Operational procedures and output 66 7.3.2. Implications associated with anomalous crayfish behaviour 66 7.3.3. Proposed amendments to review of consents safeguards (Candover) 67 7.4. Recommendations 69 7.4.1. Mitigation and enhancement 69 7.3.2. Future work 70
8. References 71
Appendix 1 77 Appendix 2 79 Appendix 3 81 Appendix 4 84 Appendix 5 87 Appendix 6 88
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Executive Summary
Background Flow augmentation schemes exist on the Candover Stream and River Alre (collectively known as the Upper Itchen flow augmentation schemes), two upper tributaries of the River Itchen Site of Special Scientific Interest (SSSI) / Special Area of Conservation (SAC). The Upper Itchen flow augmentation schemes are owned and operated by the Environment Agency (EA). The EA are working with Southern Water Services Limited to better understand how these schemes may be used to maintain water levels and quality in the lower reaches of the catchment during low flow conditions, and it was agreed that the schemes would be operated during summer / autumn of 2011 to test its effectiveness in meeting these objectives.
Concerns have been raised of the potential for flow augmentation to have a localised impact on the ecology of these chalk river headwaters; specifically on the regionally important resident population of the internationally endangered white-clawed crayfish Austropotamobius pallipes. The Hampshire and Isle of Wight Wildlife Trust (HIWWT) were contracted to undertake ecological monitoring of the Candover Stream and River Alre during testing of their respective flow augmentation schemes.
During the initial stages of ecological monitoring, and prior to the operation of the flow augmentation schemes, a proportion of crayfish at the Upper Fobdown survey site on the Candover Stream were observed exhibiting anomalous diurnal behaviour. Testing of the Upper Itchen flow augmentation schemes was postponed whilst molecular analysis was undertaken to ensure that this did not represent an outbreak of the pathogen Aphanomyces astaci, commonly known as ‘crayfish plague’. Once confirmed that ‘crayfish plague’ was not the causative agent of this behaviour, it was agreed that additional crayfish behaviour monitoring would be undertaken on both the Candover Stream and River Alre, but at distinct degrees of detail.
Objectives 1. To determine whether concerns regarding a number of the potential ecological impacts associated with the operation of the flow augmentation schemes, in particular their effect on the resident population of white-clawed crayfish, are valid; 2. To analyse and discuss the findings of the crayfish behavioural monitoring, identifying possible explanations for the occurrence of increased diurnal behaviour through a detailed literature review and consultation with national experts; 3. To identify the potential implications of, and to, the operation of the Candover Stream and River Alre flow augmentation schemes in the context of the discussion points raised from Objectives 1 and 2.
Ecological Monitoring This monitoring included drift net surveys to assess the effect of increased water velocity upon passive drift of white-clawed crayfish, particularly juveniles, and a range of other key macroinvertebrate groups. Physico-chemical and water quality monitoring was also undertaken, with a number of abiotic factors including water temperature, dissolved oxygen and nutrient levels monitored.
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Drift net surveys did not identify an effect of flow regime or flow rates on levels of crayfish drift on either the Candover Stream or the River Alre. However, the number of crayfish recorded per survey during crayfish behaviour monitoring declined across the study, and it is considered possible that there were unrecorded effects of the Upper Itchen flow augmentation schemes on white-clawed crayfish; these include an undetected increase in levels of drift during the night or increased energetic costs associated with foraging or maintaining position within the channel, particularly during the ramp-up period of operation.
Although there were a number of trends in macroinvertebrate drift with flow, there was not a conclusive relationship between flow patterns and the numbers of drifting organisms associated with either scheme, and there were no apparent trends in other target macroinvertebrate groups and no correlation between diversity and flow rate or survey day. Pre- and post augmentation samples of the benthic macroinvertebrate community at Abbotstone Causeway recorded an increase in the number of taxa following the operation of the Candover Stream scheme. However, it is important to emphasize that this result is based upon single pre- and post-augmentation samples.
Flow rates on the Candover Stream during the test period of the augmentation scheme were comparable with levels during summer / autumn flood events in previous years, and were significantly higher than at the same period during seven of the previous eleven years. Maximum daytime water temperatures on the Candover Stream recorded a significant reduction as flow rates increased, but there was no such correlation between water temperature and the operation of the River Alre scheme. Reduced maximum daytime water temperatures during a seasonal period when they should be at their highest could have a negative impact upon the development of juvenile crayfish, and both these findings provide evidence to support the need for the stable, slowly incremented operation of both schemes.
The majority of chemical variables tested were within water quality standards set by Water Framework Directive (WFD) or River Itchen Special Area of Conservation (SAC) targets, with the exception of the first three recordings of soluble reactive phosphate (orthophosphate) taken from the River Alre, and levels for most variables remained relatively constant throughout the study.
Anomalous Crayfish Behaviour There was no significant effect of the Candover Stream flow augmentation scheme on the expression of anomalous crayfish behaviour at Upper Fobdown, no evidence that the expression of anomalous behaviour extended downstream to Lower Fobdown with the operation of the scheme, and no evidence that the expression of anomalous behaviour was present in the River Alre sub-population. Crayfish from exposed locations were significantly larger than those from beneath refugia and more likely to display signs of agonistic interactions and predator related injury. The reason for this anomalous behaviour is still unclear. There is no strong evidence to relate the expression of anomalous diurnal behaviour with increased population density, reduced water levels, temperature, dissolved oxygen or light levels, an acute pollution event, disease outbreak or mating behaviour.
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Conclusions and Recommendations The testing of the Candover Stream and River Alre flow augmentation schemes in Autumn 2011 resulted in immediate and significant modifications in flow rates and water levels at two regionally important locations for the nationally and internationally endangered white-clawed crayfish. Information and analysis of data collected during this test has led to the following recommendations about future use of the schemes: Ramping-up of the operation of the Candover Stream scheme should be undertaken considerably more slowly in small, regulated flow rate increases; The maximum operating output of the Candover Stream scheme should be reviewed to ensure that, under typical operating conditions, the resultant flows are not uncharacteristic of flows which could naturally be observed downstream of the discharge point; Use of the scheme as a rapid-response solution to short-term deficits or periods of high demand is inappropriate; Habitat improvements should be made on both tributaries, particularly between and downstream of the two Candover survey sites, to mitigate any undetected drift of crayfish caused by use of the schemes; Preparatory actions, such as channel maintenance and weed cutting, must be undertaken before any future use of the schemes; Ecological monitoring (including water quality analysis and crayfish monitoring) should be carried out prior to and throughout all future operations. This will allow for the detection (if present) of any adverse impacts and should result in the suspension of the scheme if necessary.
Further technical advice, guidance and discussion are required to determine the exact details of these recommendations and landowner engagement should be undertaken to ensure that any potential future operation of the scheme be accounted for in their (sympathetic) management of the watercourse.
Further monitoring work is required to determine whether there are any longer-term implications associated with the operation of the Upper Itchen flow augmentation schemes. Further study is also necessary to determine the potential continued expression of anomalous behaviour within the Candover Stream white-clawed crayfish sub-population and, if present, determine the casual factor.
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Acknowledgements The authors would particularly like to thank to Alison Matthews and Tim Sykes of the Environment Agency (Solent and South Downs Area) for their continued and invaluable support and technical guidance throughout the development, implementation and dissemination of this project.
We would like to thank Vitacress Salads Limited and the Itchen Stoke Estate for granting access permissions to undertake the ecological monitoring and crayfish behaviour surveys, and for their continuing support for the project.
We are very grateful to the following for their assistance during field surveys; Adam Cave (Environment Agency; EA), Ali Morse (Hampshire and Isle of Wight Wildlife Trust; HIWWT), Alison Barker, Andy Blincow (HIWWT), Chloe Delgery, Dave Hunter (EA), Ellie Stubbs, Emma McSwan (EA), Guy Mason, Heather Gurd, Jolyon Chesworth (HIWWT), Louise Forder (EA), Polly Whyte (HIWWT), Richard Redsull (EA), Rob Masters, Sarah Hayward (HIWWT), Sean McGrogan (EA) and Tiki Leggett (HIWWT). The authors are also very grateful to Pete Shaw (University of Southampton) for providing drift nets for the ecological monitoring.
The authors would like extend their thanks to Dave Rumble (HIWWT; statistics), Emma McSwan (EA; multi-variate statistics), Martin de Retuerto (HIWWT; comments on an earlier version of this report), Jez Hill (EA; temperature data) and Trevor Rushbrook (for comments on an earlier version of this report) for their assistance and technical advice in data analysis and the production of this report.
Finally, we are extremely grateful to Adrian Hutchings, David Holdich, Lydia Robbins (Avon Wildlife Trust), Martin Frayling (EA) Mary-Rose Lane (EA), Paula Rosewarne (University of Leeds), Paul Stebbing (Centre for the Environment, Fisheries and Aquaculture Science) Ros Wright (EA) and Stephanie Peay (University of Leeds) for their time and generosity in sharing their technical knowledge and expertise in evaluating potential causes for the expression of the anomalous crayfish behaviour observed during this study.
Work undertaken by the Hampshire and Isle of Wight Wildlife Trust was completed under two separate collaborative agreements with the Environment Agency. The white-clawed crayfish is protected under Schedule 5 of the Wildlife and Countryside Act 1981 (as amended) and all work was carried out under licences from Natural England.
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Augmentation schemes: ecological and anomalous behaviour report 1
1. INTRODUCTION
1.1. Background Flow augmentation schemes exist on two upper tributaries, the Candover Stream and River Alre, of the River Itchen Site of Special Scientific Interest (SSSI) / Special Area of Conservation (SAC). These schemes, administered by the Environment Agency, abstract groundwater from the chalk aquifer and pump it directly into the tributaries to maintain levels within the sub-catchments and the main river below during summer / autumn low flow periods. These schemes were originally intended to both maintain water levels (quantity) and water quality for a range of ecological interests (such as fish spawning grounds), and to maintain water levels in the lower reaches of the catchment to meet human consumptive and waste treatment requirements. Though there remains an on-going capacity to use these schemes, their operation has not been regularly required.
Concerns have been raised of the potential for flow augmentation to have a localised negative impact on the ecology of the river, through modification of the physical and chemical properties of these chalk river headwaters. Specific concerns have been raised of the potential impact of the schemes on the internationally endangered white- clawed crayfish Austropotamobius pallipes (Füreder et al., 2010). As part of the Environment Agency’s Review of Consents, specific studies were commissioned during stage 3 and stage 4 of this process to investigate whether the abstraction licences for the augmentation schemes have the potential to adversely affect the River Itchen SAC (Hutchings, 2004, 2005; Taylor, 2005).
However, these reports and other ‘inpromptu’ investigations (Hutchings, 2004, 2005; Taylor, 2005) emphasise that more detailed monitoring is required to understand the potential impacts of the schemes on the nationally and internationally important ecology of these headwaters.
1.2. Proposals The Environment Agency are working with Southern Water Services Limited to understand how the Upper Itchen flow augmentation schemes may be used in the future to support the target flow regime for the River Itchen SSSI / SAC, the levels of which have been determined by the Site Action Plan. To inform this process, Southern Water Services Limited requested that the Candover Stream and River Alre flow augmentation schemes be operated for an extended period through the summer / autumn of 2011; this would enable monitoring of the influence this has on water levels at their abstraction points in the lower River Itchen catchment to be undertaken. Permission from the Environment Agency was granted on the condition that the recommendations of earlier reports (Hutchings, 2004, 2005; Taylor, 2005) associated with the SAP were implemented, and that ecological monitoring was undertaken to determine the nature and severity of any impacts resulting from the operation of the flow augmentation schemes.
1.3. Remit The Hampshire and Isle of Wight Wildlife Trust (hereafter the ‘Trust’) were contacted to advise on the potential impacts of the Candover Stream and River Alre flow augmentation schemes to the resident population of native white-clawed crayfish. Following these discussions, and in consultation with Dr Kerry Evans of the Environment Agency, the Trust produced a proposed protocol (Rushbrook, 2011a) for
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the ecological monitoring of these schemes, with a specific focus on white-clawed crayfish and the wider macroinvertebrate community.
The Trust was subsequently contracted to lead the ecological monitoring during the operation of the Upper Itchen flow augmentation schemes. In addition, following the observation of a previously unrecorded anomalous (diurnal) behaviour within a proportion of the white-clawed crayfish population, the Trust was further contracted to undertake detailed monitoring of this anomalous behaviour.
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2. ECOLOGICAL CONSIDERATIONS
2.1. White-clawed Crayfish The Candover Stream and River Alre represent the most important site(s) in Hampshire for the internationally endangered white-clawed crayfish (Hutchings, 2009; Füreder et al., 2010), the only species of crayfish native to the UK (Holdich et al., 2009).
White-clawed crayfish have suffered a 95% reduction in distribution (at the 2km grid square level) in Hampshire since the 1970’s, with these two upper tributaries of the River Itchen supporting the only remaining breeding population (Rushbrook, unpublished data; Hutchings, 2009). This population consists of two medium to small ‘sub-populations’ distributed along sections of each watercourse. However, due to localised variability in habitat suitability, crayfish distribution is patchy with discrete areas supporting notably higher densities of crayfish. The middle reaches of the Candover Stream, focused around Fobdown Farm (owned by Vitacress Salads Limited), supports the highest density centres and has been the focus of most studies on the River Itchen white-clawed crayfish population over the past two decades.
Hutchings (2004) reviewed in detail the potential implications of groundwater derived flow augmentation to the Candover Stream on the crayfish population at Fobdown Farm, and outlined the key potential impacts and considerations. It is not the intention of this document to repeat the conclusions of this work, but an understanding of them is necessary and the Executive Summary of Hutchings’ (2004) report is provided in Appendix 1. In essence, the key concerns can be summarised as (i) the direct loss of crayfish from areas of suitable habitat through increased rates of drift, (ii) reduced rates of development and recruitment due to a reduction in water temperatures of the important marginal zone, and (iii) the long-term / gradual loss of suitable habitat through prolonged groundwater drawdown and associated direct impact on population levels.
The impact of these flow augmentation schemes on the River Itchen SAC were assessed during the Review of Consents process. The concerns raised in previous work (Hutchings, 2004) were addressed by defining specific environmental outcomes within the Site Action Plan (Environment Agency, 2007), that the augmentation schemes had to meet. These outcomes were that:
1. Flows and temperature must not be rapidly changed in the river downstream of the augmentation discharge point; 2. The range in flows observed under the current flow regime must be preserved.
After detailed assessment of the impacts of the schemes, the Site Action Plan states that, in summary, the following licence changes are required: Modify Candover Scheme licence to include a condition restricting use to flows (corresponding to) Hands Off Flows of 198 Ml/d at Allbrook & Highbridge or when flows at Riverside Park fall below 194 Ml/d; Replace condition in Alre Scheme licence with tiered MRF condition with a condition restricting use to flows Hands Off Flows of 198 Ml/d at Allbrook & Highbridge or when flows at Riverside Park fall below 194 Ml/d; Modify Candover Scheme licence to restrict daily abstraction to 20 Ml/d between 1st May and 31st August; Include conditions in both licences to refer to section 20 operating agreement.
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The following conditions should be included in a section 20 operating agreement to ensure that the environmental outcomes are met:
Preparatory actions before use of the schemes such as channel maintenance, weed cutting, ecological monitoring; Gradual build up of abstraction before May and phased turning off of the schemes after August; Monitoring of ecology, groundwater levels and river flows.
However, these modifications to the abstraction licences are yet to be introduced and there remains the need to agree the formal operating procedures prior to the deadline for the implementation of these modifications. The Site Action Plan originally set the deadline for the implementation of these modifications as December 2012 (Environment Agency, 2007); however, in line with revised deadlines for the modification of abstractions associated with public water supply, this deadline is now set at December 2015 (Environment Agency, personal communication). The planned testing of these schemes during the summer / autumn of 2011 provided an ideal opportunity to investigate these concerns directly, attempt to quantify any impacts of the schemes on the resident white-clawed crayfish population and associated macroinvertebrate community, and disseminate these findings so that they may inform and hopefully influence the imminent modifications to the abstraction licences as outlined above.
It is important to note that the crayfish specific elements of the ecological monitoring undertaken within this study focused only on concerns (i) and (ii) associated with the operation of the scheme as summarised from Hutching’s’ (2004).
2.2 Macroinvertebrates The Candover Stream and River Alre support an important and diverse macroinvertebrate assemblage (Exley, 2004), and a key concern of running these augmentation schemes is their potential direct negative impact on white-clawed crayfish and other macroinvertebrates through increased levels of drift (Taylor, 2005).
There are two significant components or causes of macroinvertebrate drift, although a ‘continuous’ low level of drift representative of the whole macroinvertebrate community will be present at all times (Waters, 1972; Moss, 1998; Bilton et al., 2001). The first is a result of active or behavioural drifting, a natural process by which the individual intentionally becomes entrained in the current and is a mechanism for dispersal (i.e. to locate better foraging grounds) during periods of low flows, in response to high levels of competition or as a mechanism for predator avoidance / evasion (Waters, 1972; Moss, 1998). The timing and periodicity of drift may vary between species and environmental conditions (Waters, 1972; Moss, 1998 and references therein; McIntosh et al., 2002), but levels of active drift are typically greatest during darkness (‘nocturnal drift’). This emphasis for ‘nocturnal’ or ‘crepuscular’ behavioural drift patterns are predominantly considered to be an anti-predation response (but see Ploskey & Brown, 1980), either to avoid fish feeding visually in the water column during daylight or to actively escape benthic invertebrate predators at night (Walters, 1972 [various]; McIntosh & Peckarsky, 1996 [fish]; Hammock et al., 2012 [fish and stoneflies]).
The second reason, and the process of concern for this study, is through passive or catastrophic drifting. This involves individuals being washed out, or off, of the substrate (Waters, 1972; Moss, 1998) with the entrained organism either becoming suspended within the water column (Gibbins et al., 2010 [mayflies]; Long et al., 2011
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[stoneflies]) or ‘tumbling’ downstream associated with flows adjacent to the stream bed (Lancaster et al., 2006 [caddisflies]). Entrainment within catastrophic drift has the potential to negatively affect the associated organisms in number of ways; through a reduction in the quantity and / or quality of foraging opportunities (i.e. displacement to areas with reduced or low energy foraging recourses), an increase in the risk of predation (i.e. displacement to areas with reduced refugia / shelter resources or higher predation pressures), or directly resulting in the injury, damage or mortality of the organism as a consequence of the drifting process (i.e. crushed by rolling or colliding sediment particles; predation attempts / events). Such events of catastrophic drift are often a result of an increase in the level of an environmental stressor(s) (Waters, 1972; Moss, 1998) and may represent a pollution event (Fairchild et al., 1987; Schulz & Liess, 1999), significant reduction in oxygen levels (Connolly et al., 2004), sudden changes in water temperature (Wojtalik & Waters, 1970; Scherr et al., 2010) or sudden or large increases in flow (Lancaster et al, 2006; Gibbins et al., 2010; Long et al., 2011).
The potential effect of increasing flows, specifically in association with the operation of the Candover Stream and River Alre flow augmentation schemes, on drift of white- clawed crayfish and other key macroinvertebrate groups forms the focus of this aspect of the study. An effect could be reflected in the presence / increase of particular taxa within the drift ‘community’ during the operation of the flow augmentation schemes. Furthermore, if this does represent an increase in passive or ‘catastrophic’ drift, the associated displacement of the benthic macro-fauna may also result in localised changes to the composition of stream bed macroinvertebrate communities.
2.3. Water Quality Excessive nutrient supply, particularly of phosphate, is considered to be a major factor in the decline of the state of the UK’s chalk rivers (Environment Agency, 2004). Increased nutrient input to waterbodies can lead to eutrophication, with the resulting deterioration of in-channel habitats (e.g. through the development of dense algal mats on the substrate and other plants) and associated modification of the characteristic floral and faunal communities, often resulting in the loss of important species (Mainstone, 1999). In extreme circumstances this process can lead to the rapid onset of mass mortality of larger faunal species including crayfish (Nyström, 2002) and fish (Ochumba, 1990; La & Cooke, 2011 and references therein).
Leung (2010) recorded high levels of phosphorus (soluble reactive and total) on the River Alre downstream of Alresford Pond (a large, ‘on-line’ lake), watercress beds and commercial stocked fisheries / fish farms. Although no such relationship was recorded at similar locations on the Candover Stream, the eutrophic (nutrient enriched) nature of the ‘on-line’ Grange Lake is reflected in the periodic development of algal blooms.
It is therefore considered that a number of locations on these two sub-catchments, in particular Alresford Pond and the Grange Lake, are acting as nutrient sinks or reservoirs and are considered likely to have high levels of phosphorous, both dissolved within the water column and associated with suspended and bed sediments (Environment Agency, personal communication). As a consequence, it is considered that any activity that either directly (i.e. through movement of water and / or sediment) or indirectly (i.e. from the sediment into the water column) mobilises phosphorous and other nutrients from these lakes could have devastating consequences on the habitats and associated ecology downstream.
Hutchings (2005) observed that, during a previous operation of the Candover Stream flow augmentation scheme, the Grange Lake initially acted as a reservoir for the
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additional water due to the very low levels within it at that time, delaying the onset of increased flows downstream. Furthermore, during the operation of the River Alre flow augmentation scheme, there is the potential for water to be diverted through watercress beds (to maintain water levels within), and it is considered that Alresford Pond could delay the influence of the augmentation scheme in a similar manner to the Grange Lake. Hutchings (2004), in his review of the potential impact of the flow augmentation schemes on the resident native crayfish population, recommended that the operation of these schemes occur with incremental increases in stream flow and that the schemes should simulate characteristic summer flows. The former recommendation was incorporated into the operational procedures of the Candover Stream flow augmentation scheme (Environment Agency, 2007). Despite this, there remains a concern that sudden changes or prolonged periods of augmented flow could result in the mobilisation of phosphorus, other nutrients and suspended sediment from these enriched environments.
In addition to the potential impacts of nutrient release through the mobilisation of sediment particles, the downstream movement of fine sediments could in itself result in the deterioration of these important chalk water headwaters through the modification of the habitat (Jones et al., 2011a) and associated species assemblages. This could directly affect behaviour or cause mortality in white-clawed crayfish (Reynolds et al., 2010), macroinvertebrates (Jones et al., 2011b) and important fish species (Kemp et al., 2011), which are very sensitive to such ‘pollution’ events (Holdich, 2003; Environment, 2004).
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3. AIMS AND OBJECTVIES
The aim of this report is to describe and provide analysis of the ecological and crayfish behaviour specific monitoring undertaken during the operation of the Upper Itchen flow augmentation schemes in 2011.
Objective 1 To answer four key questions intrinsically associated with the concerns raised regarding the potential ecological impacts of these schemes (Hutchings, 2004, 2005): Is there an increase in the rate of drift of crayfish (particularly juveniles) and / or macroinvertebrates associated with an incremental increase and peak flow operation of the flow augmentation schemes? Is there a change in marginal water temperatures and / or levels of dissolved oxygen associated with the flow augmentation schemes? Is there a change in water quality downstream of two large ‘on-line’ lakes associated with an incremental increase and peak flow operation of the flow augmentation schemes? How is the magnitude of any observed effects influenced by the timings, scale and duration of the individual flow augmentation schemes, and what are the observed associated implications of in-channel management?
Objective 2 To analyse and discuss the findings of the crayfish behavioural monitoring, identifying possible explanations for the occurrence of diurnal behaviour through a detailed literature review and consultation with national experts.
Objective 3 To identify the potential implications of, and to, the operation of the Candover Stream and River Alre flow augmentation schemes in the context of the discussion points raised from Objectives 1 and 2.
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4. AUGMENTATION SCENARIOS
4.1. Upper Itchen Flow Augmentation Schemes
Figure 4.1: Location of the Upper Itchen flow augmentation schemes’ pumping stations. Produced by permission: © Crown copyright and database rights 2012; Ordnance Survey 100024198 © Environment Agency.
The two flow augmentation schemes on the Upper Itchen operate at different capacities and abstract groundwater from different locations. The augmentation flow for the Candover Stream scheme is provided from three pumping stations (Figure 4.1), each of which are supplied by two boreholes with the individual potential to supply up to 6 megalitres per day (Ml/d). This scheme therefore has a maximum operating capacity of 36Ml/d, discharged from a single outflow pipe, although a series of constraints on the intensity and timing of pumping have been imposed by the Environment Agency (2007). In contrast, the augmentation flow for the River Alre scheme is provided from four pumping stations, each supplied by a single borehole with the potential to supply up to 14Ml/d. This scheme therefore has a maximum
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operating capacity of 56Ml/d. During operation, the influence or impact of these augmentation schemes on flow rates within the catchment was determined using flow data (collected every fifteen minutes) from the Environment Agency’s Borough Bridge and Drove Lane gauging weir stations for the Candover Stream and River Alre schemes respectively.
4.2 Proposed Operation of Flow Augmentation Schemes Conditions in 2011 were considered appropriate to test the schemes as groundwater levels and river flows were comparatively low. However, the schemes would not have been needed operationally during 2011 as flow rates in the River Itchen downstream were not sufficiently low at Allbrook and Highbridge to reach threshold levels.
It was originally intended that the Candover Stream and River Alre flow augmentation schemes would be operated at a number of different intensities, both in terms of duration and levels of augmentation (Rushbrook, 2011a; Appendix 2). Due to technical difficulties during initial testing of a number of pumps, the scheduled short and intermediate (Candover Stream scheme only) tests were not undertaken. A single ‘full output’ test, in keeping with the relevant constraints on intensities and timing imposed by the Environment Agency (2007), was proposed for each scheme with incremental concurrent increases / decreases in outputs at the start and end of the scheme where feasible. It was intended that the schemes would begin operation in early September, with the augmented flows increased incrementally to a maximum output in mid / late September, with full output reached on the Candover Stream scheme four days earlier than on the River Alre. Augmented flows would then be run at full output for four-and-a-half and four weeks respectively, before being reduced in a stepwise fashion to a rate slightly above natural levels by the end of October. The proposed plan for full output testing of the Candover Stream and River Alre flow augmentation schemes is provided in Table 4.1.
Table 4.1: Proposed plans for full output testing and associated monitoring of the Candover Stream and River Alre flow augmentation schemes (August 2011). Candover Stream River Alre Week Date Operating Operational Approx Operating Operational Approx Regime Stations output Regime Stations output Week 0 08/09/2011 Scheme on 1 9 Ml/d Scheme on 1 12 Ml/d Week 1 13/09/2011 Ramp-up 2 18 Ml/d Ramp-up 2 24 Ml/d Week 1 15/09/2011 Ramp-up 3 25 Ml/d Ramp-up 3 36 Ml/d Week 2 19/09/2011 Full output 3 25 Ml/d Ramp-up 4 48 Ml/d Week 2 22/09/2011 Full output 3 25 Ml/d Full output 4 48 Ml/d Week 3 29/09/2011 Full output 3 25 Ml/d Full output 4 48 Ml/d Week 4 06/10/2011 Full output 3 25 Ml/d Full output 4 48 Ml/d Week 5 13/10/2011 Full output 3 25 Ml/d Full output 4 48 Ml/d Week 6 17/10/2011 Ramp-down 2 16 Ml/d Ramp-down 3 36 Ml/d Week 6 20/10/2011 Ramp-down 1 7 Ml/d Ramp-down 2 24 Ml/d Week 7 24/10/2011 Ramp-down 1 3.5 Ml/d Ramp-down 1 12 Ml/d
4.3. Operation of Flow Augmentation Schemes The ultimate operation of the flow augmentation schemes were subject to both delay in their activation and disruption during their operation (Figures 4.2a and 4.2b). The delay was a consequence of the discovery that a proportion of the crayfish within the Candover Stream sub-population was exhibiting anomalous behaviour (see section 6.1). The situation was immediately reviewed to assess the potential implications that operating the flow augmentation schemes may have for these crayfish and their
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behaviour. The potential causes of this anomalous behaviour and its implications for future operations of the augmentation schemes are specifically discussed within later sections of this report (see sections 6.6 and 7.3).
Furthermore, disruption to the discharge output occurred on a number of occasions, predominantly as a consequence of pump failure. Disruptions in flow were particularly associated with the River Alre scheme, and the malfunction of a pipeline valve resulted in a major shut down of this scheme in mid-September. These disruptions resulted in a more haphazard flow pattern during the operation of the River Alre scheme (Figure 4.2b) than the distinct baseline, ramp-up, full output and ramp-down periods that were originally intended.
a) 0.700
0.600
0.500
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0.200 /s)
3 0.100 (m
0.000 01/09/2011 11/09/2011 21/09/2011 01/10/2011 11/10/2011 21/10/2011 31/10/2011 flows
b) 1.8
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Daily meanDaily 1.4
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0 01/09/2011 11/09/2011 21/09/2011 01/10/2011 11/10/2011 21/10/2011 31/10/2011 Date
Figure 4.2: Daily mean flows at a) Borough Bridge on the Candover Stream and at b) Drove Lane on the River Alre between 1st September and 31st October 2011 with the dates of drift surveys highlighted in red. Please note that the scales on the y-axes differ.
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5. ECOLOGICAL MONITORING
5.1. Methodology The white-clawed crayfish is listed on Schedule 5 of the Wildlife and Countryside Act 1981 (as amended). All aspects of this study that involved the capture and handling of white-clawed crayfish were completed by suitably qualified staff, under Natural England Licence Number 20112714 and / or the Natural England Licence covering all employees of the Environment Agency.
Specific responsibilities for different aspects of the monitoring and analysis were determined by the Environment Agency. All work followed relevant Health and Safety guidelines and stringent bio-security measures were imposed on all field workers.
5.1.1. Drift Drift of white-clawed crayfish and macroinvertebrates were surveyed simultaneously using the following methodology revised from Taylor (2005) and Hutchings (2005). Levels of drift were recorded at two locations on the Candover Stream, and at a single location on the River Alre. Each of the authors acted as lead surveyor for the same site throughout the study period to maintain within site continuity and consistency in the implementation of the methodology.
Figure 5.1: Locations of drift (orange circles), water quality (purple circles) and kick sample (maroon circles) survey points on the Upper Itchen. Produced by permission: © Crown copyright and database rights 2012; Ordnance Survey 100015632 © Hampshire and Isle of Wight Wildlife Trust.
Sample points (Figure 5.1) on the Candover Stream were located along Upper (SU 56801 33965) and Lower (SU 57044 33586) sections of the stream within the Fobdown Farm site boundary (hereafter known as ‘Upper Fobdown’ and ‘Lower Fobdown’ respectively), and were focused on two areas of suitable habitat known to support the greatest densities of native crayfish (Hutching, 2005, 2009).
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a)
b)
c)
Figure 5.2: Drift nets in position at a) Lower and b) Upper Fobdown Farm sampling locations on the Candover Stream and at the c) Drove Lane sample point on the River Alre.
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The single River Alre sampling point (SU 57373 32543) was situated approximately 65m downstream of Drove Lane, the location supporting the main concentration of the native crayfish sub-population, to ensure that drift from both upstream channels of the river was being captured and to minimise the risk of nets becoming displaced by the turbulent flow present immediately downstream of the Drove Lane gauging weir.
Nine drift nets (41 x 26 cm / 1066 cm² sample area; 1mm mesh size) were deployed at each site, with nets placed adjacent to each other but staggered in a downstream direction across the channel at the Candover Steam sites, (Figure 5.2a and 5.2b). Drift nets were numbered 1 through 9, with net number 1 positioned the furthest upstream and associated with the true right bank. The greater width of the River Alre and presence of localised stands of dense macrophytes precluded this formation, but nets were distributed across the channel in a standardised pattern that maximised the coverage across its width (Figure 5.2c). As an increase in levels of passive drift was a key concern associated with the operation of the flow augmentation schemes, collection of drift samples was undertaken during daylight hours to minimise the influence of macroinvertebrates actively entering the water column (see section 2.2 for further detail). Furthermore, this avoided the logistical / Health and Safety complications associated with undertaking survey work at night.
Nets were deployed at approximately 10am on each survey day and collected drifting biotic material for a period of five hours before being removed, the samples washed within the net and the contents emptied into individual containers. Each individual container was then separately transferred to a white tray on the river bank for sorting. Any crayfish were removed immediately and the following information recorded: sex, carapace length, presence of physical damage, evidence of disease, breeding condition, moult stage (see section 6.2.1. for further details). All captured crayfish were then returned into the margins immediately downstream of the surveyed area and in the areas of lowest flow.
Table 5.1: Macroinvertebrate groups recorded within the drift investigation (excluding white- clawed crayfish).
Scientific Name Common Name Classification Level
Mollusca snail / bivalve / limpet Class Hirudinea leech Class Plecoptera stonefly Order Tricoptera cased caddisfly Order Tricoptera caseless caddifly Order Baetidae olive mayfly Family Ephemerellidae blue-winged olive Family Ephemeridae burrowing mayfly Family Heptageniidae flat-bodied mayfly Family Ephemeroptera all other mayfly Order Gammaridae freshwater shrimp Family
The remainder of the sample was subsequently sorted live on the bank with the presence and abundance of a number of key macroinvertebrate groups recorded (see Table 5.1). These groups were selected for one or more of the following criteria:
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Their propensity to become entrained in ‘catastrophic drift’ during periods of increased flow (Borchardt, 1993 [mayfly, freshwater shrimps]; Holomuzki & Biggs, 2003 [cased caddisfly, mayfly and snail]; Long et al., 2011 [stonefly]); Their importance in monitoring river health (based on their BMWP family scores); Their prey value for apex predators such as crayfish (Reynolds & O’Keeffe, 2005; Johnston, 2011) and fish (Wallace & Webster, 1996; Wootton, 1998; Hendry & Cragg-Hine, 2003).
At the Candover Stream sites, samples were sorted for a period of 10 minutes and the abundance of removed individuals from the key taxa groups recorded. Due to the substantial accumulation of leaf litter within the drift nets, on specific occasions samples were further washed where necessary by ‘floating’ the leaves as part of the 10 minute sort time. Conversely, samples collected at the River Alre site were subject to a single, systematic search through all material collected, with the abundance of removed individuals from the key taxa groups recorded as above. At all sites, once sorted the whole sample was then returned to the watercourse.
Baseline surveys Monitoring was undertaken to determine ‘normal’ baseline levels of white-clawed crayfish and macroinvertebrate drift. Initial baseline surveys were undertaken at the three sites prior to the scheduled short and intermediate tests (Rushbrook, 2011a; Appendix 2), on the 28th June, 1st July and 5th July 2011. However, following the cancellation of these earlier tests and subsequent delay in the initiation of full output testing, the requirement for further baseline surveys was identified to avoid the potential influence of seasonal variation on relative abundances and a single additional survey was undertaken at the Drove Lane site. Conversely, an additional three surveys were undertaken at the Fobdown Farm sites, a consequence of the expression of anomalous behaviour within the crayfish sub-population and the subsequent extended delay in operation of this scheme (see section 6.1). All sampling followed the protocol outlined above.
Monitoring surveys Monitoring of the operational Upper Itchen flow augmentation schemes followed the protocol outlined above and was undertaken during September and October. A total of eleven and twelve surveys were undertaken at the Drove Lane and Fobdown Farm sites respectively (Figure 4.2), with the additional Fobdown Farm surveys undertaken during the ramp-up period. Live sorting of the samples in situ enabled a dynamic assessment of the potential effects of the flow augmentation schemes to be undertaken; mechanisms were in place for the immediate suspension of the schemes if certain threshold levels were reached with regards to their impact on white-clawed crayfish drift (Table 5.2; see Appendix 3 for detail of calculation).
Table 5.2: Threshold levels for the suspension of the Upper Itchen flow augmentation schemes reflecting the total number of crayfish recorded within the drift nets during a single survey. Scheme Site Number of crayfish in nets
Candover Stream Upper Fobdown 8
Candover Stream Lower Fobdown 3
River Alre Drove Lane 3
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Invertebrate Community Depletion Standard three minute kick samples (Environment Agency, 2012a) were collected from the Candover Stream at Abbotstone Causeway (SU 56400 34449), situated approximately 1.1km upstream of the Upper Fobdown survey site. A single sample was collected during the Environment Agency’s standard spring (31st May) and autumn (27th October) macroinvertebrate survey periods (Environment Agency, 2012a), to determine the benthic community before and after augmentation testing. Collected samples were initially emptied into a large tray in situ to allow for the removal of any crayfish or fish species present. Samples were subsequently transferred to a small bucket and returned to the Environment Agency laboratory where the samples were preserved in 40% formaldehyde.
Each sample was analysed using a methodology adapted from Environment Agency (2012b) protocol. Prior to identification, samples were separated into three fractions for ease of processing using a stack of three sieves with mesh sizes of 4mm, 1mm and 500µm. All invertebrates were identified to family level (or appropriate level of classification as determined by the Biological Monitoring Working Party scoring system), and abundances recorded. The total number of individuals removed from the sample was the measure of abundance used for all groups with the exception of Gammaridae, Oligacheata, Ephemerellidae and Baetidae, whose abundances were calculated (completely or in part) using estimated values from sub-samples of these fractions. In addition, 50 Gammaridae individuals were removed from across the three fractions for each sample to check for misidentification of Crangonyctidae.
Biological Monitoring Working Party (BMWP) scores, Average Score per Taxa (ASPT) and Lotic-invertebrate Index for Flow Evaluation scores were calculated for each sample.
5.1.2. Physico-chemical Temperature data loggers were deployed at a fixed position at each of the drift net survey sites during the first summer baseline survey (28th June), and remained in-situ for the duration of the ecological monitoring (27th October). The in-situ data loggers recorded the water temperature at 15 minutes intervals at the Upper and Lower Fobdown sites, and 15 minutes +1 second intervals at the Drove Lane site. Data loggers were deployed downstream of the drift nets and located at the margins of the survey areas to a) focus on those habitats important for the development of juvenile white-clawed crayfish, to b) ensure that they were sheltered from increased flow rates during the operation of the schemes and c) to ensure temperature readings were not skewed by the effect of direct solar radiation on the metal probes.
Additional physico-chemical data was collected during each drift survey from the Upper and Lower Fobdown survey sites. Water depth immediately upstream of the frame of each drift net was recorded to measure the proportion of the total collection area that could physically collect invertebrate drift, or its ‘catch effort’. This was not necessary at Drove Lane as water levels were substantially greater than the height of the nets and nets were therefore fully submerged during all surveys. Recordings of sub-surface (approximately first 10cm) water temperature, dissolved oxygen (DO) and pH were taken immediately downstream of the drift nets at five points across the width of the channel using a hand-held gauge. Readings were collected to provide a series of instantaneous ‘snapshots’ of the response of the water temperature and chemistry within these channels to the direct addition of groundwater.
In keeping with stringent bio-security measures and to avoid the potential transfer of biological pathogens between the Candover Stream and River Alre, no readings were
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collected at Drove Lane as disinfection of the hand-held probe was not feasible since the use of disinfectant on the probe would have damaged / affected the sensitivity of the equipment.
5.1.3. Water Quality Water samples were collected on both the Candover Stream and River Alre to monitor potential mobilisation of nutrients and / or sediments from the Grange Lake and Alresford Pond respectively.
An Environment Agency routine water quality (chemical) monitoring point (G0006200) exists downstream of the Grange Lake on the Candover Stream, located immediately upstream of Abbotstone Causeway (SU 56373 34567), and provided a long term baseline dataset. However, additional monitoring at a more sensitive scale was undertaken to ensure that potential nutrient / sediment ‘mobilisation’ events were not missed by the routine (monthly) surveys. This allowed for a more accurate assessment of any observed effects in terms of the nature of any enrichment, the timing, and association this had to the operation of the flow augmentation scheme. Concurrent sampling was undertaken at a novel sampling site, The Soke, downstream of Alresford Pond (SU 58803 32977).
Samples were collected on the same day as drift surveys (including autumn baselines) following the standard collection procedure of the Environment Agency (2010) and sent out for chemical analysis. The samples were analysed using the Environment Agency RivF analysis suite, which included suspended solids and orthophosphate (i.e. soluble reactive phosphorus), with an additional test for total phosphorus. The latter was added in light of Leung’s (2010) findings indicating the elevation of total phosphorus on the River Alre.
5.1.4. Statistical Analysis Statistical analysis was performed using Microsoft® Excel 2003 and 2007 for graphical analysis and Minitab® 14.0 for all other statistical testing unless otherwise stated.
Drift-net surveys The separation of flow data into discrete groups was considered desirable, and it was proposed within the original methodology that comparisons would be made between baseline, ramp-up, full-output and ramp-down periods (Rushbrook, 2011a). The operation of the Candover Stream scheme and associated relatively smooth changes in flow patterns allow for this categorisation to be made. However, due to licence restrictions (for surveying white-clawed crayfish) and the extension of full output operations, only a single ramp-down survey was undertaken at all three sites. This was not included as a separate category as its single value would dramatically undermine the power of any statistical testing. The operation of the Candover Stream flow augmentation schemes was therefore categorised into three discrete groups based on flow rates, reflecting the associated modifications in the operation of the scheme (regime 1 = baseline; regime 2 = ramp-up / down; regime 3 = full output) and is illustrated in Figure 5.3.
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Flow Regime 1 223
0.650
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0.500 /s) 3 0.450
Flow (m Flow 0.400
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0.250 01/09/2011 11/09/2011 21/09/2011 01/10/2011 11/10/2011 21/10/2011 31/10/2011
01/09/11 – 18/09/11 19/09/11 – 28/09/1129/09/11 – 22/10/11 23/10/11 – 31/10/11 Figure 5.3: Flow regime groups used for statistical analysis of Fobdown Farm survey sites based upon daily mean flows at Borough Bridge on the Candover Stream between 1st September and 31st October (with dates of drift surveys annotated in red).
The separation of the flow data for the River Alre scheme into discrete groups was not considered appropriate due to the irregular flow patterns (Figure 4.2b) associated with the various disruptions to its operation. Though this limited the amount of statistical testing that could undertaken, it was considered that little confidence could be attributed to any findings associated with statistical testing where the data was ‘forced’ to fit those flow regimes applied to the Candover Stream scheme.
The following statistical testing was performed on the results from all three drift sample sites independently, to allow for a greater weight of testing on the potential effect of augmented flows on the levels of drift. This was considered appropriate as it would minimise the baseline environmental variability (e.g. channel width, depth, baseline flows, substrate type(s) and complexity, etc) that would exist between the three sites and their associated invertebrate communities. Furthermore, the extended delay in the operation of the Candover Stream scheme (see sections 5.1.1 & 6.1) and the disruption to flow patterns on the River Alre, with the associated differences in timings and validity in separating flow data into discrete regimes, provides further justification for the separate analysis of the two schemes.
A total of eight samples (Lower Fobdown: n = 4; Drove Lane: n = 4) were excluded from the drift analysis due to drift nets becoming dislodged and overturned by the flow with the loss of some or all of the sample assumed or observed. Furthermore, a single sample from the Upper Fobdown site was removed from the multivariate analysis executed using the Primer-E software as no target invertebrates were recorded. All continuous variable data was tested for normal distribution using the Anderson-Darling normality test. Data that deviated from normal distribution was first Log10- or arcsine square root-transformed (as appropriate) to normalise the variance and subsequently tested using parametric statistics. Discrete data or data sets that could not be normalised were tested using non-parametric equivalents.
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For each survey at the three sites, both the exact number of individuals in each target group collected per net (raw data) and the ‘catch’ of individuals per unit of effort (CPUE) were analysed using multivariate statistics. The CPUE was calculated by dividing the number of individuals collected by the proportion of the ‘wetted area’ of the net (i.e. the area that was submerged and therefore capable of collecting drifting invertebrates).
Due to the limitations in sample size for each of the regime groups and the associated conservative nature of the above testing (i.e. risk of returning non-significant results where differences actually exist) graphical analyses were first performed for each site to see if any general trends in levels of a) crayfish specific or b) invertebrate drift could be identified. The number of crayfish, the total number of invertebrates, and the number of individuals for specific taxon collected across all nine nets combined was plotted against survey number and flow to investigate whether there was a trend associated with these factors.
To determine whether there was a difference among target invertebrates groups in drift community composition across the study, data was pooled for all nets per survey and Shannon-Wiener indices of diversity were calculated. One-way ANOVA (with Fisher’s individual error rate post-hoc testing) were performed to test for an effect of flow regime (Figure 5.3) on the diversity of the drift communities at the two Fobdown Farm sites only. The potential correlation between Shannon-Wiener diversity index with survey day (i.e. survey day 1 = autumn baseline survey 1) and flow rate was tested using Pearson’s and Spearman’s rank correlation tests as appropriate.
For more detailed analysis, multi-variate testing was performed on data from Upper and Lower Fobdown sites using the Primer-E (version 6) statistical software. Data from Drove Lane was excluded as the flow data could not be separated into discrete flow regimes with any genuine confidence. For both raw and CPUE data, a Multi- Dimensional Scaling (MDS) plot was created to provide a visual representation to help determine whether there were any similarities (or clustering) of the invertebrate drift data at Upper and Lower Fobdown based on the three flow regimes. The Bray-Curtis coefficient was the similarity measure used. An Analysis of Similarities (ANOSIM) test (R) was then performed to test the similarities shown on the MDS plots. ANOSIM tests the null hypothesis that there is no difference in drift net communities between flow regimes. The closer the computed R-value is towards 1 the higher the degree of separation between the flow regimes, though the significance of this value is dependent on the test results rejecting the null hypothesis.
BEST tests were then performed to analyse whether the multivariate biotic patterns could be linked to suites of abiotic (environmental) variables and, if so, determine which abiotic variables best describe the biological spread. The abiotic variables included in the analysis for the Fobdown Farm sites were: flow (daily mean) on day of survey, flow on day prior to survey, water temperature, dissolved oxygen (DO) and pH. Water temperature, DO and pH were determined by calculating the mean of the five cross-channel readings taken using the hand-held probe at each survey. In keeping with stringent bio-security measures, specifically concerns of the potential transfer of biological diseases between the Candover Stream and River Alre site via the hand-held probe, only flow on day of survey and flow on day prior to survey was collected at Drove Lane. Therefore, the Drove Lane drift data was excluded from this analysis.
Invertebrate Community Depletion Invertebrate abundances were Log10–transformed and a graphical comparison of the pre- and post-augmentation samples by taxa was undertaken. Furthermore, to
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determine whether there was a general trend for a lower abundance within individual families between the two sample visits, a statistical sign test was performed. Finally comparisons of BMWP, ASPT and LIFE scores and Shannon-Wiener diversity index were made.
Physico-chemical The effect of the augmentation scheme on water temperatures between the 1st September and 26th October was investigated. Firstly, daytime water temperatures were assessed and the period between 16:00 and 17:00 considered to be most consistently associated with maximum water temperatures. Maximum daytime water temperatures for this period were therefore determined by calculating the mean temperature between 16:00 and 16:59 using readings recorded by the in-situ probes. This figure was used to determine whether there was an effect of the operation of the flow augmentation schemes on the summer high water temperatures considered important for juvenile crayfish (Reynolds, 2002; Hutchings, 2009). Average flow rates from Borough Bridge and Drove Lane for the corresponding period were used in the analysis of the Candover Stream and River Alre schemes respectively. Ambient temperature data recorded at the Environment Agency’s weather station at Otterbourne (SU 46730 23490) was used for measures of daily maximum and minimum ambient temperatures. For each site, Spearman’s rank correlation tests were performed between maximum daytime water temperatures and mean daily flows, between maximum daytime water temperature and daily maximum ambient temperature, and between daytime maximum ambient temperature and mean daily flows.
Overnight water temperatures were also calculated to exclude the potential that the effects of solar radiation were concealing the scale of any temperature reductions caused by the flow augmentation schemes Overnight water temperature was determined by calculating the mean temperature between 01:00am to 01:59am, and average flow rates were calculated using corresponding flow data as above. For each site, Spearman’s rank correlation tests were performed between overnight water temperatures and flow rates, between overnight water temperature and daily minimum ambient temperature, and between daily minimum ambient temperature and mean daily flows.
Flow data from the Candover Stream between 2000 and 2010 was plotted against flow data during 2011. To compare the flow rates during the augmentation scheme with baseline levels, Wilcoxon-signed rank tests were performed on the flow data between 1st September and 31st October 2011 with each of the previous eleven year classes separately. More detailed analysis of the influence of the flow augmentation schemes on the hydrology of the River Itchen catchment will be provided in a report currently being compiled by Atkins Limited (Environment Agency, personal communication).
Water Quality The levels of a number of chemical variables across the monitoring period was analysed against water quality standards for the relevant sections of the River Itchen catchment (Table 5.3). The data for a number of these variables collected at Abbotstone Causeway was compared with the results of the Environment Agency’s routine water quality (chemical) monitoring at this location during 2010.
Daily mean flow rates within the Candover Stream and River Alre for the period between the 1st July and 31st October were plotted and graphically compared against each of these variables to identify any potential associations between flow rates and / or flow patterns with the level of these chemicals within the watercourse.
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Table 5.3: Chemical variables tested during water quality monitoring with threshold levels for high water quality and associated determining legislation.
Standard for High Factor Type Level Determiner Water Quality
Water Framework Ammonia < 0.6mg/l General 90-percentile Directive* Water Framework Biological Oxygen Demand < 2.5mg/l General 90-percentile Directive† Water Framework Dissolved Oxygen > 70% General 10 -percentile Directive* Soluble Reactive Phosphate Candover Habitat Directive < 0.04mg/l average (orthophosphate) - Candover Stream specific Review of Consents Soluble Reactive Phosphate River Alre Habitat Directive < 0.06mg/l average (orthophosphate) - Alre specific Review of Consents pH - - - -
River Itchen Habitat Directive Suspended solids < 10μg/l average specfic Review of Consents
Total Phosphate - - - -
* Threshold for good ecological status † Not used as a determinate of good ecological status
5.2. Results
5.2.1. Drift and associated abiotic factors A total of eight and one white-clawed crayfish were recorded across the 12 drift net surveys at Upper and Lower Fobdown survey sites respectively, with no crayfish recorded during any of the 11 drift net surveys at Drove Lane. There was no trend in the occurrence and number of crayfish collected at Upper Fobdown (Figure 5.4).
4
3
2 Number of crayfish of Number 1
0 024681012 Survey number Figure 5.4: Number of crayfish recorded across all nine nets combined during each of the twelve drift net surveys undertaken at the Upper Fobdown site. Vertical (dashed) lines represent flow regime boundaries.
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Graphical analysis The total number of (target) invertebrates collected varied considerably between the two tributaries, with a greater number of invertebrates collected in each of the River Alre (Drove Lane) surveys than was recorded during any surveys at either Candover Stream site. Baetidae mayfly nymphs constituted a large proportion of the drift community at all sites, with freshwater shrimp (Gammaridae) also a very important component at Lower Fobdown, Drove Lane and Upper Fobdown to a lesser degree (Table 5.4). Other important groups included cased and caseless caddisfly larvae (Trichoptera) and snails / limpets / pea mussels (Mollusca). White-clawed crayfish constituted only a very small proportion of the drifting community at the two Fobdown sites, and (as outlined above) were not recorded in drift surveys at Drove Lane.
Table 5.4: Relative abundances of all recorded target taxa across all drift net surveys for each of the three sites. Values for the three most commonly recorded taxa within the drift for each site are represent in bold, with the single most dominant group annotated in red
Taxa Upper Fobdown Lower Fobdown Drove Lane Astacidae 1.19 0.13 0.00 Mollusca 23.59 1.89 6.53 Hirudinea 0.15 0.50 3.66 Plecoptera 0.15 0.25 0.40 Tricoptera (cased) 2.52 10.08 9.26 Tricoptera (caseless) 15.43 1.89 4.46 Baetidae 38.72 40.81 33.11 Ephemerellidae 0.59 5.79 3.86 Ephemeridae 1.04 0.25 0.27 Heptageniidae 0.59 0.00 0.00 Ephemeroptera 0.74 0.00 0.07
Gammaridae 15.28 38.41 38.37
At Upper and, to a lesser degree, Lower Fobdown sites, there was a trend for an increased level of drift as flow rates were increased during the ramp-up (i.e. flow regime 2) period of the Candover Stream flow augmentation scheme; this was followed by a dramatic reduction in numbers of drifting invertebrates as flow rates reached maximum levels and a general trend for a more steady decline as flow rates plateau (Figure 5.5). At Drove Lane, there was an immediate decline in the number of invertebrates collected with the initiation of the River Alre scheme, reaching a temporary plateau before recording a secondary peak during the later stages of the scheme’s operation (Figure 5.6).
There was a substantial decline in the numbers of Baetidae mayfly nymphs collected at all three sites with the operation of the respective flow augmentation schemes (Figure 5.7). This decline was most rapid at Drove Lane, following the general trend shown by the total number of invertebrates, with Baetidae numbers dropping steadily at the Fobdown sites with the onset of augmentation. There were no apparent trends associated between flow regime and any other target invertebrate group, but both Upper and Lower Fobdown sites recorded a sharp increase and associated peak number of freshwater shrimps (Gammaridae) on survey 6 (Figure 5.7).
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a) 100
90
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70
60
50
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Total number of invertebrates collected 20
10
0 123456789101112
b)
0.7
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0.5 /s) 3
0.4
0.3 Mean daily flow (m flow daily Mean 0.2
0.1
0 123456789101112 Survey Number
Figure 5.5: The a) total number of invertebrates from target groups recorded in Upper (solid line) and Lower Fobdown (dashed line) during drift surveys and the b) corresponding mean daily flow rates associated with those surveys. Vertical (dashed) lines represent flow regime boundaries.
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a) 250
200
150
100
Total number invertebrates of Total collected 50
0 1234567891011
b) 1.600
1.500
1.400 /s) 3
1.300
1.200 Mean daily flow (m flow daily Mean
1.100
1.000 1234567891011
Survey Number Figure 5.6: The a) total number of invertebrates from target groups recorded at Drove Lane during each drift survey and the b) corresponding mean daily flow rates associated with those surveys.
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a) Baetidae Gammaridae
50 35 45 30 40 35 25 30 20 25 20 15 15 10 10 5 5 0 0 024681012 024681012
b)
60 70
50 60 50 40 40 30 30 20 20 10 10 0 0 024681012 024681012
c)
100 120 90 80 100 70 80 60 50 60 40 30 40 20 20 10 0 0 024681012 024681012 Survey Number Survey Number Figure 5.7: Number of Baetidae and Gammaridae collected across all surveys at a) Upper Fobdown, b) Lower Fobdown and c) Drove Lane. Note that survey numbers for the Fobdown and Drove Lane sites are not directly comparable (see section 5.1.1), and that vertical (dashed) lines represent flow regime boundaries (Fobdown sites only).
There was a significant difference in diversity (Shannon-Wiener Index) among the target invertebrate groups between flow regimes at Lower Fobdown (One-way ANOVA: F2,9 = 5.44, p = 0.028; Figure 5.8), but not at Upper Fobdown (One-way ANOVA: F2,9 = 1.15, p = 0.360; Figure 5.8), with drift net communities less diverse under flow regime 2 (ramp-up / -down) compared with regime 3 (full output) at Lower Fobdown (Fisher’s post-hoc test).
Upper Fobdown Lower Fobdown
1.8 1.6
1.6 1.4
1.4 1.2 1.2 1 1 0.8 0.8 0.6 0.6 0.4 0.4 0.2 0.2 Mean of Shannon-Wiener Index 0 0 123 123 Flow Regime Figure 5.8: Mean diversity for drift communities per flow regime at Upper and Lower Fobdown. Error bars represent one standard deviation.
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No correlations were identified at any of the three sites between diversity and flow rate (Spearman’s rank correlation: [Upper] rs = 0.329, N = 12, p = 0.297; [Lower] rs = 0.336, N = 12, p = 0.286; Pearson’s rank correlation: [Drove] r = 0.218, N = 11, p – 0.520) or survey day (Pearson’s correlation: [Upper] r = 0.172, N = 12, p = 0.593; [Lower] r = 0.373, N = 12, p = 0.232; [Drove] r = 0.237, N = 11, p = 0.416).
For more detailed multivariate analyses of the two Fobdown sites, samples with missing data (i.e. nets overturned and sample lost) and an outlier sample (i.e. no target invertebrate drift recorded) had to be removed to allow for effective analysis. No transformation was applied to the biological data as the abundances were small and this would not cause the data to be skewed.
The pair-wise ANOSIM results for both the raw and catch per unit effort (CPUE) data identified little difference in invertebrate drift between different flow regimes (Table 5.5). A number of pair-wise flow regime comparisons at both Upper and Lower Fobdown identified statistically significant differences, indicating that the resultant invertebrate drift data was not random and this was explained by flow regime to some degree. However, the R-statistic in all cases was very low, signifying that differences between invertebrate drift as a result of differing flow regimes was very small. For example, the most significant result recorded, which was within the CPUE data for Lower Fobdown, had an R-statistic of 0.197 (with p = 0.1%) for flow regime 1 versus flow regime 3. R-statistics are values between 0 and 1 making 0.197 equivalent to almost 20%, which suggests that nearly 20% of the difference in invertebrate numbers could be attributed to the change from flow regime 1 to regime 3. Conversely, 80% of the difference is attributable to a non-flow regime effect.
Table 5.5: Significance levels and corresponding R-statistics for pair-wise comparison of invertebrate data by flow regime with significant results shaded. Pairwise Flow R statistic % Significance regime level Raw data Upper Fobdown 1 vs 2 0.017 20.8 1 vs 3 0.004 41.1 2 vs 3 0.031 8.1 Lower Fobdown 1 vs 2 -0.005 49.8 1 vs 3 0.085 1.4 2 vs 3 0.133 0.1
CPUE Upper Fobdown 1 vs 2 0.002 44.1 1 vs 3 0.073 3.9 2 vs 3 0.061 0.8 Lower Fobdown 1 vs 2 -0.019 72.6 1 vs 3 0.197 0.1 2 vs 3 0.153 0.1
BEST was performed to examine the extent to which the physico-chemical data is related to (“explains”) the observed biological pattern. Again, significant differences were recorded for Upper and Lower Fobdown, indicating that the resultant invertebrate drift data was not random and this was explained by one or a combination of physico-chemical factor(s) to some degree (Table 5.6). However, as with the pair-
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wise ANOSIMs, all significant results are associated with very low correlation values, indicating that a large amount of the difference is not attributable to that factor(s).
Table 5.6: Significance levels and corresponding correlation values for the BEST correlated variable(s) to explain invertebrate data. Significant results are shaded. BEST correlated Correlation % Significance level Variable Raw Data Upper Fobdown Temperature 0.168 1
Lower Fobdown Temperature 0.101 10
CPUE Upper Fobdown Temperature 0.176 1
Previous day Flow, Lower Fobdown 0.127 1 Temperature, pH
5.2.2. Invertebrate Community Depletion at Abbotstone Causeway A total of 1810 and 2618 individuals were identified respectively in the pre- and post augmentation benthic samples from Abbotstone Causeway. Higher numbers of total taxa, taxa unique to the sample and BMWP scoring taxa were recorded in the post augmentation sample (Table 5.7). Furthermore, a considerably higher BWMP score was recorded for the post-augmentation sample, although APST was lower and LIFE scores were very similar.
Table 5.7: Results of pre- and post augmentation benthic invertebrate surveys at Abbotstone Causeway. N = total number of taxa recorded, NØ = number of taxa which were unique to that sample and NBMWP the number of BMWP scoring taxa BMWP Sample Type N N N ASPT LIFE Ø BWMP Score Pre 31 3 30 173 5.77 7.36
Post 38 10 36 203 5.64 7.35
ASPT is the standard measure used to compare benthic invertebrate samples, with differences of <0.5 considered to represent ‘noise’ in the sample (Environment Agency, personal communication). It is therefore considered that there was no evidence of a general depletion in invertebrate groups between samples, nor was there evidence of a reduction in the sensitivity of the invertebrate community to organic pollution.
When directly comparing individual taxa, there was no significant trend in the abundances between the two samples (sign test: N = 41, p = 0.749). However, there were a number of notable differences both between the individual ‘families’ (Figure 5.9) and some of the taxonomic orders. There was a considerable reduction in the number of Ephemerellidae mayfly larvae and Oligochaeta (segmented worms) between the pre- and post augmentation surveys, but conversely there was a dramatic increase in the numbers of Baetidae mayfly, Goeridae and Hydroptillidae caddisfly larvae, freshwater shrimp (Gammaridae), riffle beetle (Elmidae) larvae and black fly larvae (Simulidae). Stonefly larvae (family Perlodidae) were completely
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absent for the second sample, but two new mayfly groups, the Heptageniidae and Leptophlebiidae, were recorded.
3.5
3
2.5
2
1.5 Log Abudnance 1
0.5
0 Dixidae Sialidae Elmidae Baetidae Asellidae Physidae Goeridae Corixidae Caenidae Ancylidae Haliplidae Dytiscidae Pediciidae Simuliidae Valvatidae Bithynidae Perlodidae Planariidae Piscicolidae Oligochaeta Sphaeriidae Planorbidae Hydracarina Lymnaeidae Gammaridae Hydroptilidae Ephemeridae Erpobdellidae Limnephilidae Chironomidae Heptageniidae Odontoceridae Calopterygidae Rhyacophilidae Glossiphonidae Ephemerellidae Leptophlebiidae Hydropsychidae Polycentropodida Sericostomatidae Cordulegasteridae Figure 5.9: Log abundance for all taxa recorded during benthic invertebrate surveys. Hatched bars represent pre- and shaded bar post augmentation sample values.
5.2.3. Physico-chemical There was a highly significant negative correlation between flow rates within the Candover Stream and maximum daytime water temperatures at both Upper and Lower Fobdown sites (Table 5.8), with a decrease in temperature associated with increasing flow. Conversely, there was no correlation between flow rates and overnight temperatures (Table 5.8).
Table 5.8: Spearman’s rank correlations comparing the relationship between flow rate (Flow), water temperature (WT) and ambient temperature (AT) at each of the three sites. Overnight WT / Min AT Daytime WT / Max AT Factors N rs p-value rs p-value WT vs Flow 56 -0.171 0.207 -0.565 <0.001 Upper WT vs AT 56 0.839 <0.001 0.703 <0.001 Fobdown AT vs Flow 56 -0.110 0.418 -0.057 0.679 WT vs Flow 56 -0.090 0.510 -0.365 0.006 Lower WT vs AT 56 0.860 <0.001 0.818 <0.001 Fobdown AT vs Flow 56 -0.110 0.418 -0.057 0.679 WT vs Flow 56 -0.177 0.192 -0.138 0.311 Drove Lane WT vs AT 56 0.802 <0.001 0.811 <0.001
AT vs Flow 56 -0.032 0.816 0.066 0.630
There was a highly significant positive correlation between maximum daytime water temperatures and daily maximum ambient temperature at Upper and Lower Fobdown (Table 5.8), and graphical analysis demonstrates the subtleness of this change in maximum daytime water temperatures, a consequence of the apposing influence that
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concurrent increases in flow rates and maximum ambient temperatures appear to be applying (Figure 5.10a and 5.10b). Furthermore, there was a highly significant positive correlation between overnight water temperatures and daily minimum ambient temperature (Table 5.8), but no correlation between either measure of ambient temperature and flow rates (Table 5.8).
a) 30 0.7
0.6 25
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5 0.1 /s) 3 0 0 01/09/2011 12/09/2011 23/09/2011 04/10/2011 15/10/2011 26/10/2011 b) 30 0.7 Flow rates rates (m Flow Temperature (°C) 0.6 25
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0 0 01/09/2011 12/09/2011 23/09/2011 04/10/2011 15/10/2011 26/10/2011 Date
Figure 5.10: Comparison of maximum daytime water (solid black line, open squares) and daily maximum ambient (dashed line, open diamonds) temperatures with daily mean flow rates (solid line, closed triangles) at a) Upper Fobdown and b) Lower Fobdown survey sites.
Similarly, there was a highly significant positive correlation between measures of ambient temperature and its associated measure of water temperatures at Drove Lane (Table 5.8), and there was no correlation between either measure of ambient temperature and flow rates (Table 5.8). In contrast to the Fobdown sites, there was no correlation between flow rates on the River Alre and either maximum daytime or overnight water temperature at Drove Lane (Table 5.8).
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Flow rates for the period between 1st September and 31st October in 2011 were significantly higher than during the corresponding period for seven of the previous eleven years (Table 5.9; Appendix 4). Of the remaining four years, flow rates were only significantly higher than 2011 during 2001, when unseasonably heavy rain and associated widespread autumnal flooding was recorded across south-east England.
Table 5.9: Results of Wilcoxon signed-rank tests to compare flow rates at Borough Bridge on the Candover Stream between 1st September and 31st October 2011 (inclusive) with the corresponding period during the previous eleven years. Year N N for test Z- Value p-value Median 2000 61 61 1130 0.186 0.02 2001 61 61 385.5 <0.001 -0.08 2002 61 61 1475.5 <0.001 0.06 2003 61 61 1627 <0.001 0.12 2004 61 61 1525 <0.001 0.08 2005 61 61 1891 <0.001 0.17 2006 61 61 1807.5 <0.001 0.16 2007 61 61 936.5 0.951 0.00 2008 61 61 703 0.082 -0.03 2009 60 60 1727 <0.001 0.14 2010 61 61 1591.5 <0.001 0.09
5.2.4. Water quality Throughout the study, the recorded levels for the majority of the chemical variables analysed were within acceptable levels based upon high water quality standards for the relevant reaches of the River Itchen catchment (Table 5.10). The exception to this was the high levels of soluble reactive phosphate (orthophosphate) recorded within a number of the samples collected from The Soke (River Alre). Furthermore, where applicable the range of levels recorded at the Abbotstone Causeway sample point during the ecological monitoring were consistent with the range of values recorded during routine water quality (chemical) monitoring throughout 2010 (see Appendix 5).
Determining patterns in the levels of these chemical variables is difficult, and all conclusions should be treated with caution due to the limited number of samples in comparison to flow data. On the River Alre, there is an immediate response to the onset of flow augmentation (increased flow) with a dramatic reduction in levels of ammonia (Figure 5.11a) and soluble reactive phosphate (Figure 5.11b), with the latter continuing to steadily decline through the monitoring. In addition, after a short lag, there is a similar dramatic reduction in total phosphate levels (see Appendix 6). There is a degree of fluctuation in the levels of other variables on the River Alre, but none demonstrate an obvious pattern associated with flow rate (see Appendix 6).
The levels of chemical variables recorded on the Candover Stream are generally more stable, with variability where present not obviously associated with flow rates (see Appendix 6). The only exception is the presence of two peaks in suspended solid levels during the ramping-up period of the Candover Stream scheme.
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Table 5.10: The range and mean values of the specific chemical variables measured during ecological monitoring.
Candover Stream River Alre Standard for Factor High Water Range Mean Range Mean Quality
Ammonia (mg/l)* 0.03 0.03 0.051 - 0.368 0.104 < 0.6
Biological Oxygen Demand 1.0 - 1.4 1.1 1.0 - 1.4 1.2 < 4 (mg/l)†
Dissolved Oxygen (%) 85.9 - 156.0 109.4 81.4 - 131.4 103.3 > 70
Soluble Reactive Phosphate 0.02 - 0.036 0.022 - - < 0.04 (mg/l) - Candover* Soluble Reactive Phosphate - - 0.035 - 0.186 0.078 < 0.06 (mg/l) - Alre
pH 7.56 - 8.04 7.87 7.52 - 7.85 7.67 -
Suspended solids (mg/l)† 3 - 4.35 3.25 3 - 5.88 4.28 < 10
Total Phosphate (mg/l)* 0.02 - 0.046 0.025 0.047 - 0.259 0.100 -
† A number of samples contained concentrations below the low est level of detection for this variable at both sites. * A number of samples contained concentrations below the low est level of dection for this variable at Abbotstone Causew ay
5.3. Discussion As discussed above (see section 5.1.4), it was considered important that the results from each site were analysed separately to ensure that no site-specific effects of the scheme were concealed by combining the data. Within this section, each site is first discussed individually, then cross-site comparisons of the results are made (as appropriate) to identify general trends or explain differences in the response of sites to augmented flow. Cross-comparisons have been made to provide a greater depth of detail to inform and, as necessary, mitigate against any potential effects associated with the future use of these schemes. However, all comparison must be assessed with caution, as intrinsic site differences such as total / relative abundance of target invertebrate groups have not been directly tested and as such associated inferences have been made.
5.3.1. Flow Augmentation, Water Levels and Flow Rates The operation of the Candover Stream flow augmentation scheme resulted in a 66% increase in flow rates at Borough Bridge in the first four days of operation, and a greater than 80% increase during the initial ten day period. This was associated with an approximately 50% increase in water depth at both Upper and Lower Fobdown sites, and a visible increase in wetted area at Upper Fobdown (including the submergence of previously exposed marginal berms).
The operation of the River Alre flow augmentation scheme resulted in a greater than 50% increase in flow rates and a discernible increase in water depth. However, the effects of the augmented flows were not as easily observed, partly due to the greater size and associated natural capacity of the River Alre compared with the Candover Stream, but also as a consequence of its disrupted operation.
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a) 1.8 0.4
1.6 0.35
1.4 0.3
1.2 0.25 /s)
3 1.0 0.2 0.8 Flow (m 0.15 0.6 Ammoniacal Nitrogen (mg/l) 0.1 0.4
0.2 0.05
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011
b)
1.8 0.2
1.6 0.18
0.16 1.4
0.14 1.2 0.12 /s) 3 1.0 0.1 0.8 Flow (m 0.08 0.6
0.06 Orthophosphate (mg/l)
0.4 0.04
0.2 0.02
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date Figure 5.11: Comparison of flow rates (closed triangles) with levels of a) ammoniacal nitrogen and b) soluble reactive (ortho-) phosphate (open squares) on the River Alre at The Soke.
During events associated with rapid increases in flow rates, large numbers of animals may be displaced or lost from a specific point and transported downstream, a phenomenon widely referred to as passive or catastrophic drift (Waters, 1972; Moss, 1998). A number of studies have shown that passive drift increases in parallel with discharge or flow rates; an increase in discharge typically results in higher water velocities and corresponding levels of shear stress with an associated increase in dislodgement of animals from the substrate (Walters, 1972, Brittain & Eikeland, 1988; Borchardt, 1993, Lancaster, 1999). If shear stress exceeds the sediment entrainment threshold, the bed becomes unstable and particles are partially or fully set in motion (Gibbins et al., 2005, 2010). This movement can result in substrate interstices no longer offering a refuge from disturbance, whilst animals present on the surface of entrained particles will be carried downstream with the substrate (Gibbins et al., 2010).
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All sites supported a heterogeneous substrate composition with the inclusion of large and static features such as cobbles, boulders, bedrock and complex tree root systems at the Fobdown sites, and dense stands of in-channel macrophytes at Drove Lane. These types of features have been shown to be important in reducing levels of invertebrate (Holomuzki & Biggs, 2003, Long et al., 2011) and crayfish (Nyström, 2002; Benvuento, et al., 2008; Clark et al., 2008) drift and associated mortality. The lowest level of particulate sorting and greatest size and density of large cobbles is considered to be associated with the Upper Fobdown site, and this site is therefore considered to have been subject to the lowest levels of substrate entrainment. In contrast, the Lower Fobdown site is considered to exhibit the greatest homogeneity of substrate and provide the fewest fixed or large potential refugia. Sediment entrainment was not directly investigated (but was observed at all sites) and these assumptions cannot be confirmed from the data collected in this study. However, anecdotal evidence does exist to support the theory that substrate stability was greater at Upper Fobdown Farm, since this was the only site not to experience displacement of nets and associated loss of samples.
5.3.2. Flow Augmentation and White-clawed Crayfish Incidence of crayfish capture within the drift net surveys was low or absent at all sites and there was no evidence that crayfish drift differed between flow regimes, was influenced by flow rates, or differentially affected age classes at any of the three sites. However, within the crayfish behavioural monitoring, there was a negative correlation between the total number of crayfish recorded and the duration of the study at both Fobdown sites (see sections 6.4.1 & 6.4.2). Increased levels of passive or catastrophic drift would potentially have direct adverse impacts on the white-clawed crayfish population. These impacts can either be direct, through damage or mortality associated with drifting (i.e. collisions with static or mobile substrate, increased risk of predation), or indirect such as displacement to inferior habitats in terms of foraging and sheltering resources.
The increase in flow rates during the ‘ramping-up’ stage of the Candover Stream scheme was considerably more dramatic than originally intended, both in terms of the size of increments and the reduced lag period between. This was a consequence of the extended delay in the operation of the scheme associated with the identification of anomalous behaviour among crayfish at Upper Fobdown, and a lower than expected capacity to control discharge from each of the pumping stations (Environment Agency, personal communication). Furthermore, though based on the number of crayfish collected within the drift nets there was no evidence of any effect during the ramping- up of the scheme, at the Upper Fobdown site there was a notable reduction in the total number of crayfish collected per survey across the duration of the crayfish behavioural monitoring, and a corresponding non-significant reduction in the level of expression of the anomalous behaviour (see section 6.4.1, Table 6.2). These findings could indicate a short-term loss of individuals to drift as crayfish acclimatised to a rapid and substantial increase in change in flow rates.
During this concurrent crayfish behavioural monitoring, crayfish were recorded across the width of the channel, with juveniles predominantly associated with the shallower stream edges and larger individuals with cobbles and boulders in deeper waters as expected (Demers et al., 2003; Hutchings, 2009). However, there was no evidence of behavioural adaptations such as avoidance of areas of high velocity with increasing flow rates, which is in contrast to a number of studies where white-clawed crayfish and closely related astacid species avoided refugia in areas of high flow ([white-clawed crayfish] Benvenuto et al., 2008; Pearson, 2011 and references therein; [stone crayfish Austropotamobius torrentium] Streissl & Hödl, 2002). However, high densities
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of crayfish were only recorded at the Upper Fobdown site, and any such behavioural adaptations may have been concealed by the proportion of crayfish expressing anomalous behaviour. In fact, a number of such crayfish were observed clasping on to vegetation to maintain their position on the upper side of large flints even during the periods of greatest flow rates. Furthermore, no attention was paid to crayfish posture, a common response among many species of crayfish to increased flow rates, where individuals adopt a more streamlined body shape (Maude & Williams, 1983; Clark et al., 2008).
The size and heterogeneity of substrate particles is known to affect drift rates in aquatic invertebrates (Holomuzki & Biggs, 2003; Lancaster et al., 2006; Long et al., 2011), with heterogeneous habitat types that include larger particle types (i.e. cobbles and boulders) offering the best resistance to increased flow. Among lotic crayfish populations, a high level of habitat complexity or heterogeneity is very important due to differentiation in microhabitat utilization between age classes (Demers et al., 2003; Benvuento, et al., 2008; Hutchings, 2009). The presence of shallow water with complex tree root systems and dense marginal vegetation is therefore considered to be as important as deeper water with large cobbles and boulders in determining the ability of the crayfish ‘population’ to respond to increased flow rates (Nyström, 2002, Pearson, 2011). Therefore, the maximum tolerable flow velocity for white-clawed crayfish will be determined by the range, size, shape and associated stability of available refuges; since in addition to the increased risk of drift, high flow rates can result in the downstream displacement of bed substrate with the associated loss of refuges (inherently increasing the risk of drift) and even direct damage or mortality of crayfish (Demers et al. 2003; Robinson et al., 2000; Pearson, 2011). The three drift sites studied were selected due to their locally superior habitat availability for crayfish and associated greater densities of individuals. It was considered important to select such sites as any adverse effects on white-clawed crayfish at these localities would have a significant impact on the viability of the Upper Itchen population. However, this selection may therefore have influenced the results of this drift study as they represent the areas of greatest habitat complexity and associated amelioration of increased flow conditions resulting from the operation of the flow augmentation schemes. This raises concerns that the impacts of the augmentation scheme on white-clawed crayfish may be variable at a localised level, with implications that unrecorded drift could have occurred in areas with lower refugia availability or suitability. Though those locations potentially at risk will not be the key high density centres, crayfish distribution is typically patchy (Holdich, 2003; Peay, 2003, Hutchings, 2009) and the loss of a significant proportion of crayfish from these areas could result in further fragmentation of what is already considered to be discontinuous population.
Though flow rates recorded during the scheme are within the natural flow range for the sites, these values are comparable with winter or summer flood levels and significantly higher than seven of the previous eleven years for the same time period. White-clawed crayfish possess seasonal patterns in behaviour, becoming decreasingly active with the onset of late autumn / early winter and moving into deeper water or sheltering within burrows (Barbaresi & Gherardi, 2001; Gherardi, 2002). Therefore, this microhabitat utilisation and decreased levels of activity will limit their exposure to and resulting implications of these high winter flow rates. However, during the summer and early autumn crayfish will be actively foraging, during which time they move away from sheltered locations and seek out exposed locations to feed (Clavero et al., 2009), making them more vulnerable to drift. Even accounting for the anomalous diurnal behaviour observed at Upper Fobdown, it is considered that most foraging crayfish would express typical nocturnal foraging behaviour. Therefore, it is possible that undetected levels of drift overnight may have been associated with the
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operation of the augmentation scheme. This potential implication cannot be tested within the design of these monitoring studies.
The direct loss of crayfish from these sites through drift or mortality are the most acute implications of the increased flows, though other chronic effects may be associated with the operation of the Upper Itchen flow augmentation schemes. During the concurrent behaviour monitoring, a number of crayfish were observed to become entrained within the flow, and a proportion were observed to swim (through rapid and extended tail flexing) and successfully re-associate themselves with the substrate or associated features at a distance of less than 3m downstream. Others were observed to be actively moving against the flow, or attaching themselves to rocks and associated vegetation to maintain their position within the watercourse. Though not tested as part of this study, it is considered highly likely that there are increased energetic costs imposed on crayfish by the increased flow rates associated with the flow augmentation schemes. This may be as a direct cost associated with moving within the current, effectively reducing the net gain of foraging activities. Alternatively, crayfish may become decreasingly active with increased flow ([Orconectes obscurus] Clark et al., 2008), avoiding typical foraging grounds due to the associated exposure to increased flow, and therefore suffering a reduction in energy intake. This could have implications for somatic growth, particularly for juveniles which typically undergo rapid growth in their first year, and fecundity in sexually mature individuals due to slower or reduced gonad development (Reynolds, 2002). If there is a net depletion in energy levels associated with the flow augmentation schemes, then extended operation of these schemes may increase the risk of ‘exhausted’ individuals becoming entrained within the drift and displaced to sites of lower habitat suitability. Furthermore, its repeated use over two or more years could have substantial implications on recruitment during subsequent years.
Water temperature plays a very important role in crayfish ecology (Nyström, 2002), and influences the timings of behaviour (Gherardi, 2002 and references therein). Disruptions to the typical cyclical pattern of water temperatures may have an adverse impact on white-clawed crayfish recruitment and development. Specifically, growth in crayfish only occurs above a certain temperature and, among temperate water species such as white-clawed crayfish, temperature is a fundamentally important factor in influencing moult frequency and therefore growth (Reynolds, 2002). A reduction in temperatures during late summer / early autumn could therefore have negative impacts through retardation of crayfish growth rates. These could be particularly significant within the year 0+ age class, for which rapid growth through a series of short inter-moult periods is fundamentally important in influencing crayfish survival, both for the avoidance of gape-limited predators and preparations for reduced activity during winter.
There was evidence that the operation of the augmentation scheme affected water temperatures at the Upper and Lower Fobdown sites, with maximum daytime – but not overnight – water temperature significantly reduced as flow rates increased. This would indicate that the augmentation of additional cool groundwater limited the ability of the marginal areas to heat up through solar radiation, but as water temperature naturally cools during the night the influence of additional groundwater is lost. However, determining the degree of significance of this impact associated with the scheme is complex, since there were also significant positive correlations between water and ambient temperatures. However, the presence of this negative correlation between flow rates and daytime temperatures, when water temperatures should be at their highest and so important in influencing growth rates at this critical time for juveniles, indicates that there is an effect of the augmented flows on the water temperature of the Candover Stream. This is of particular concern, and it is
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considered likely that any temperature changes associated with the operation of the Candover Stream scheme will adversely impact white-clawed crayfish by reducing juvenile survival rates. Furthermore, the repeated or long-term use of this scheme is also considered likely to impact on future recruitment within this sub-population.
There was no correlation between water temperatures and the operation of the River Alre scheme, with water temperature only (positively) correlating to ambient temperatures. It is considered that this is likely to be both a consequence of the lower input of this scheme relative to the total volume of water within the River Alre, and the irregular flow patterns associated with the disrupted operation of this scheme.
Since white-clawed crayfish populations associated with chalk river catchments are adapted to relatively stable flow and temperature conditions, it is considered that the above findings provide further evidence for the importance of a stable, slowly incremented operation of both the Candover Stream and River Alre schemes (Hutchings, 2009). The turbulent nature of rapid or variable changes in flow may not only have an increased propensity to cause drift compared with more stable, laminar increases in flow, but may cause irregular fluctuations in water temperature with potential disruptions to crayfish behavioural or ecological cycles.
Finally, though not included within the remit of this study, it is important to highlight the potential long term implications of these schemes. Previous testing and modelling has demonstrated that the longer term impact of the Upper Itchen flow augmentation schemes is to reduce the flows during the subsequent winter, with impacts carrying over to the following summer but to a lesser degree (Environment Agency, personal communication). However, it is considered that the scheme’s impacts on winter levels and its capacity to continue into the summer months (and associated severity) will be dependent on the degree to which groundwater levels were already suppressed (prior to operation) and the provision of sufficient winter re-charge of the aquifer. Since the scheme is designed to alleviate low water flows and increase water levels to, in part, meet abstraction demands, it is inherently likely to be drawing from an already depleted groundwater supply. Therefore, without sufficient winter re-charge of the aquifer, it is considered highly likely that the impacts associated with groundwater drawdown over an extended period could have an adverse effect on the crayfish population, particularly at Fobdown Farm. Specifically, this would include (taken from Hutchings, 2004): Low flows in autumn / winter and the following spring / early summer could result in increased adult and juvenile mortalities as traditional refuges are lost, increasing interaction between age classes and exposure to predation, Low flows will lead to changes in habitat conditions, slower current velocity, increasing siltation, reduced marginal zone, infilling of refuges by silt will result in increasing fragmentation of the population, Elevated nutrient and depressed dissolved oxygen levels could lead directly to crayfish mortalities.
However, if used sensitively, it is important to note that the operation of the Upper Itchen flow augmentation schemes during periods of extreme drought would benefit fish, white-clawed crayfish, and other aquatic invertebrates by providing a secured supply of water essential for their survival. Extreme drought in this instance would be considered to represent the extensive or complete loss of suitable sheltering and foraging habitat, either through a significant reduction in the wetted width or modification of habitat characteristics associated with the reduction in flow (i.e. increased deposition of fine substrates). The occurrence of such circumstances should be determined following discussions between suitably qualified ecologists on site.
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5.3.3. Flow Augmentation and Invertebrate Drift The total numbers of invertebrates recorded per survey at Drove Lane were consistently larger than at either Fobdown site. Graphical comparisons of flow rates and the total number of drifting individuals at the two Fobdown sites illustrate a potential response in the numbers of drifting organisms to the rapid increases in flow rates, followed by a subsequent tailing off of invertebrate numbers. This may reflect an increase in drift associated with increased flow in the short term, with levels of drift subsequently declining as those organisms most susceptible to drift were either gradually lost from the area or were deposited / able to locate areas with suitable refuge from flow. This trend was most strongly associated with Upper Fobdown, but it must be emphasised that at neither site was there a conclusive relationship between flow patterns and numbers of drifting organisms. In comparison, there was an immediate dramatic decline in total numbers at Drove Lane in response to the first increase in flow, an increase and a smaller peak in numbers during the later stages of the study, with relatively stable numbers in the drift both between and after.
At all sites, Baetidae mayfly nymphs accounted for a third or more of all target individuals collected. At Lower Fobdown and Drove Lane, a combination of Baetidae nymphs and freshwater shrimp comprised over 79% and 71% of all drifting target taxa respectively, with approximately a further 10% accounted for by cased caddisfly larva. At Upper Fobdown however, the close to 40% Baetidae mayfly nymph component, in combination with molluscans, caseless caddisfly and freshwater shrimps, accounts for over 93% of total drift within the target groups.
Baetidae mayfly nymphs are a common component in passive or catastrophic drift, susceptible to both direct dislodgement and entrainment on mobilised sediment (Holomuzki & Biggs, 2003; Gibbins et al., 2010 and references therein). This is considered to be a consequence of microhabitat utilisation, as Baetidae mayfly nymphs have fixed gills and actively seek areas of higher velocity to aid respiration, their streamlined shape enabling them to maintain a position on exposed surfaces where velocities are greater and where their oxygen demands can be met (Lancaster & Beylea, 2006). However, this preference for areas of higher water velocity is likely to result in Baetidae nymphs being readily lost through drift where flow rates are naturally or artificially raised, which is consistent with the findings of this study. Furthermore, due to the relative importance within the drift community, it is unsurprising that rates of Baetidae mayfly drift have a strong influence in total drift at all three sites, with this similarity in drift patterns particularly evident at Drove Lane.
Numbers of freshwater shrimp within the drift dramatically increased during the middle of the study at both Fobdown sites, corresponding to the onset of peak flow rates associated with the Candover Stream scheme. Conversely, freshwater shrimp numbers at Drove Lane follow the same pattern as Baetidae mayfly. Despite their similar patterns, nearly three times as many freshwater shrimp were recorded in drift nets at Lower Fobdown compared with Upper Fobdown (N = 305 vs. 103), and more than five times the number at Upper Fobdown were collected at Drove Lane. Though a highly mobile invertebrate and able to withstand greater levels of flow (and associated shear stress) than other freshwater organisms (e.g. Ephemerellidae mayfly nymphs), freshwater shrimps are not intrinsically suited to flowing environments (Hynes, 1970), and significant population losses have been recorded at shear stress values well below that required for the movement of the surface layer of inorganic substrate (Borchardt, 1993). This would support the trend in the numbers of freshwater shrimp within the drift at the Fobdown sites. Furthermore, within this study Borchardt demonstrated that freshwater shrimp utilise refugia more efficiently and to a greater extent than some other taxa, and a behavioural response to these high flows
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could explain the sharp decline in this trend at these sites. In addition, the perceived greater levels of refuge availability and substrate stability at the Upper Fobdown site, could explain the lower number of freshwater shrimp recorded within the drift. No other notable trends were identified within the target macroinvertebrate groups recorded.
Multivariate analysis found no evidence that the ‘community composition’ of target invertebrates within drift at the two Fobdown survey sites was affected by flow regime, influenced by flow rates (both on the day of and day prior to survey) or any of the other environmental variables tested at the Candover Stream sites. However, there was a significant difference between flow regimes in community diversity at the Lower Fobdown survey site. The Shannon-Wiener index of diversity responds most strongly to changes in the importance of the rarest species (Peet 1974, referenced in Nagendra, 2002), and the differences observed at Lower Fobdown appear to be associated to an increase in the relative importance of cased caddisfly larva and a reduction in freshwater shrimp during flow regime three. However, there was no consistent trend in the effect of flow regime or flow on diversity within the individual sites, and it is therefore considered that neither flow nor any other abiotic variables had a consistent significant effect on the composition of the (target) invertebrate drift community.
5.3.4. Flow Augmentation and Invertebrate Community Depletion There was no evidence of invertebrate community depletion at Abbotstone Causeway following the operation of the Candover Stream scheme. Indeed, there were notable increases within the post augmentation sample in the number of recorded taxa, number of taxa unique to that sample and in the BMWP score; with similar values for the ASPT and LIFE scores returned. The timing of these surveys was selected to reflect the spring and autumn survey protocol adopted by the Environment Agency (2012a). The observed increase in the number of taxa and BMWP score is inconsistent with trends observed during routine monitoring of other chalkstream sites, with BMWP scores and species richness typical greater within spring samples. However, it is important to emphasise that the comparisons made within this study are based on a single pre- and post augmentation sample. Furthermore, a number of alternative explanations associated with the operation of the flow augmentation scheme require discussion.
Firstly, due to an unseasonably dry spring, flow conditions within the Upper Itchen were already depleted (see Appendix 4) by the time of the late spring / pre- augmentation survey, and this was reflected in a lower than expected return from the survey. The section of the Candover Stream surveyed has a high level of in-channel vegetation and substrate heterogeneity, partially a result of recent (2009) habitat enhancement work. Habitat complexity / substrate heterogeneity positively correlates to species richness and diversity, and the operation of the Candover Stream flow augmentation scheme and associated increase in water levels would encourage re- colonisation of this section as marginal areas become re-wetted and in-channel vegetation developed. An associated active upstream colonisation of these areas by macroinvertebrates would explain the increase in the number of taxa and unique taxa, BWMP ‘families’, and associated BMWP score recorded. However, the observed differences in richness were largely attributed to changes in the large and middle size fraction of the samples. With the exception of freshwater shrimp, those groups that ‘returned’ or increased within the autumn / post-augmentation sample (e.g. Heptageniidae and Leptophlebiidae mayfly nymph, riffle (Elmidae) beetle larvae, Hydroptilidae caddisfly larvae, blackfly (Simulidae) larvae, etc) are generally poor
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upstream dispersers during their juvenile stage, and their active upstream movement to this location is considered unlikely.
A second, perhaps more probable, explanation is that colonisation has occurred in a downstream direction, associated with continuous (active) or catastrophic (passive) drift. Studies have shown that active drift can be triggered by a reduction in flow conditions with invertebrates actively seeking more suitable habitat conditions (Minshall & Winger, 1968; Poff & Ward, 1991), though this response is not universal (Dewson et al., 2007). Conversely, organisms entrained within passive drift during high flow conditions are inherently more likely to return to the substrate in areas of low flow or flow refugia. Due to habitat conditions (i.e. homologous substrate, reduced particle size), invertebrates within the substrate immediately upstream of Abbotstone Causeway are considered to be susceptible to drift, and therefore provide a potential source for the increase in abundance and richness at this site observed in the post- augmentation sample. If the high level of habitat complexity in this section is an important factor for the observed increase in the abundance and richness in the later sample, separating whether this is a direct (through active colonisation) or indirect (through accumulation of drifting organisms) effect is not possible from the data collected in this study.
5.3.5. Flow Augmentation and Water Quality Throughout the duration of the operation of the Candover Stream scheme, levels of each chemical variable analysed remained within (and often significantly below) the water quality standards set by the Water Framework Directive or SAC targets (as relevant). Furthermore, with the exception of pH, levels remained relatively steady; only a gradual decrease in dissolved oxygen and minor increases in biological oxygen demand and suspended solids demonstrated any degree of association with the operation of the augmentation scheme. However, as all levels remained within acceptable ranges, it is considered that there was no significant effect of the Candover Stream flow augmentation scheme on water quality.
Patterns between flow rates and water quality variables in the River Alre were more complex, though all were within acceptable limits with the exception of soluble reactive (ortho-) phosphate. Prior to the operation of the River Alre scheme, levels of soluble reactive (ortho-) phosphate substantially exceeded threshold levels based on SAC targets. This could be a consequence of the low water levels present at this time, leading to an increase in concentration of orthophosphate through a lack of dilution. However, it is not uncommon for chemical samples from the River Alre to fail to meet its SAC targets for orthophosphate. To address this issue, through the Review of Consents process (undertaken in 2004) a number of modifications to discharge licences on the River Alre have been proposed, and are set to come into effect in December 2012 (Environment Agency, personal communication). Given the inherent water quality problems associated with the Alre (Leung, 2010), it is difficult to determine whether the presence of low flows was simply coincidental or were actually exacerbating this situation.
The onset of the flow augmentation scheme resulted in a dramatic decrease in level of soluble reactive (ortho-) phosphate, with levels dropping to within acceptable standards by the fourth survey. Levels of total phosphate followed a similar pattern to the soluble component. The observed reduction is phosphates could suggest a beneficial influence of augmentation, with the increased volume of water acting to dilute phosphate concentrations. The average (ortho-) phosphate concentration in the groundwater discharged at the Alre Scheme outfalls was 0.028 mg/l, which is similar to the background levels observed in nearby rivers and streams with no local sources
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of phosphate. This is compared with average levels of 0.046 mg/l recorded during the test upstream of the outfall at Drayton and 0.18 mg/l recorded in the River Alre at The Soke before the test started. Simple volumetric calculations show that dilution of the higher phosphate concentrations in the river by the augmentation water does not totally account for the drop in concentrations observed in the river. It is therefore likely that there is significant fluctuation in phosphate levels caused by upstream activities, which may partially account for the fall in levels. There is no apparent evidence of significant mobilisation of phosphate from Alresford Pond.
During the study levels of ammonia superficially showed a similar pattern to phosphates. However, the decline in levels actually corresponds to the period prior to the onset of augmentation (between survey 1 and 2), and it is therefore more likely to be associated with changes in upstream discharges rather than the operation of the River Alre scheme. This may support the theory that upstream discharges may have a greater impact on water quality than the augmentation schemes. A longer term data set would be needed to confirm this. Biological oxygen demand, dissolved oxygen and suspended solids also all showed some degree of association with flow rates, but even greater caution is recommended on putting too much emphasis on these inferences. Therefore, it is considered that there is no evidence to suggest a significant effect of the River Alre flow augmentation scheme on water quality.
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6. ANOMALOUS CRAYFISH BEHAVIOUR
The white-clawed crayfish is listed on Schedule 5 of the Wildlife and Countryside Act 1981 (as amended). All aspects of the study that involved the capture and handling of white-clawed crayfish were completed by suitably qualified staff, under Natural England Licence Number 20112714 and / or the Natural England Licence covering all employees of the Environment Agency.
6.1. Background During baseline monitoring undertaken on the 5th September, the expression of a previously unrecorded anomalous diurnal behaviour was observed among a proportion of the white-clawed crayfish at the Upper Fobdown survey site. Specifically, a number of crayfish could be observed moving or sitting out on open gravels or climbing upon the sides or tops of large flints (Figure 6.1). Crayfish are nocturnal (Gherardi, 2002; Holdich, 2003) and such behaviour has never been observed at Fobdown Farm (Hutchings, personal communication; Rushbrook, personal observations), despite the site being subject to detailed monitoring since the mid 1990’s (Hutchings, 2009) and visited by the authors earlier that same year.
Figure 6.1: Crayfish out on open gravel demonstrating anomalous diurnal behaviour.
The initiation of both Upper Itchen flow augmentation schemes was postponed whilst the cause and extent of the expression of this behaviour was investigated. Diurnal behaviour forms part of the typical behavioural pattern for white-clawed crayfish infected by Aphanomyces astaci, commonly referred to as ‘crayfish plague’. A.astaci is a fungal-like disease introduced into the UK with non-native crayfish species from North America, specifically the signal crayfish Pacifastacus leniusculus, and can cause up to 100% mortality within infected white-clawed crayfish populations (Oidtmann, 2000; Evans & Edgerton, 2002). The potential that this observation represented an outbreak of crayfish plague was a key factor in the postponement of the operation of the scheme, since an increase in flow rates could facilitate the dispersal of infective zoospores and therefore the spread of crayfish plague. An
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alternative explanation provided for this behaviour was that infection with the chronic, yet ultimately lethal, porcelain disease was the causative factor (Stebbings, personal communication). Gross signs of porcelain disease include the development of an opaque white “porcelain-like” colouration to the musculature, particularly within the abdomen or tail (Oidtmann, 2000; Figure 6.2). This represents the microsporidian parasite Thelohania contejeani reproducing within the host’s muscle tissues, eventually filling the cells, and culminating in the death of the individual (Imhoff et al., 2009).
a) b)
Figure 6.2: Ventral views of a) parasitized (opaque white colouration to abdomen) and b) unparasitized white clawed crayfish (translucent abdomen).
Following consultation with a number of national experts, no agreement could be reached as to whether this represented an incidence of crayfish plague and it was decided that a small sample would be sent to the Centre for the Environment, Fisheries and Aquaculture Science (Cefas) for analysis. Six white-clawed crayfish (four expressing diurnal and two ‘normal’ behaviour), with three (two and one) suspected to be infected with porcelain disease, were collected and sent to Cefas. The removal and transfer of white-clawed crayfish for pathogenic and parasitic analysis was performed under the Natural England Licence covering all employees of the Environment Agency.
Concurrently, the extent of this behaviour within the population was monitored with detailed examination (manual searching; see section 6.2.1) undertaken at the Fobdown sites on the 7th and 8th September, and all three drift net survey sites on the 12th September. The anomalous behaviour was not identified at either the Lower Fobdown or the Drove Lane survey site. Following these investigatory surveys and subsequent discussions between the Environment Agency, Natural England and the Trust, it was concluded that the expression of this behaviour was confined to the Candover Stream and that the River Alre flow augmentation scheme could be operated (13th September). Furthermore, with the confirmation that none of the white- clawed crayfish sent to Cefas were infected with A. astaci, it was agreed that the Candover Stream flow augmentation scheme could be operated (19th September). However, due to the continued expression of the anomalous behaviour at the Upper
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Fobdown site and the failure to identify its cause, it was agreed that monitoring would be undertaken at all sites with three specific purposes:
1. To provide safeguards against the potential for the operation of the Candover Stream scheme to exacerbate existing stressors / put additional strain on crayfish within the Upper Fobdown survey section (i.e. an increase in the percentage of the population expressing anomalous behaviour); 2. To ensure that the scheme was not acting as a vector to increase the downstream expression of this behaviour (i.e. to the Lower Fobdown section); and 3. To ensure the River Alre sub-population continued to show no evidence of these abnormalities.
Due to the different statuses of the two crayfish sub-populations, specific monitoring protocols were devised for the Candover Stream and River Alre sites.
6.2. Methodology – Candover Stream The Candover Stream, specifically the Upper and Lower Fobdown survey points, formed the focus for the crayfish anomalous behaviour monitoring. The methodology adopted for the Fobdown Farm sites was adapted from the techniques used by Hutchings (2009) during his long-term monitoring (10+ yrs) study of white-clawed crayfish at Fobdown; this study used the corresponding survey sections to allow for direct comparison (Upper Fobdown = section 2; Lower Fobdown = section 7).
6.2.1. Manual Searches Thirty minute manual searches were undertaken within the two survey sections at Fobdown by a single surveyor. This provided a standard Crayfish Per Unit Effort (CrPUE), corresponding to the total number of crayfish recorded per survey.
Working in an upstream direction, characteristic crayfish habitat patches (i.e. clean gravels of varying particle size underlying large flints, cobbles and woody debris) were identified and investigated for the presence of crayfish using a purpose built survey viewer (allowing the surveyor to see the stream bed more clearly; Figure 6.3). Cobbles / large stones, bricks, woody debris and other potential natural refugia were lifted or turned, the bed beneath allowed to clear and the area inspected for crayfish. Where appropriate, any stones beneath were also lifted until the gravel, sand or soft substrate beneath was encountered and this was examined for crayfish and their burrows. Concurrently, the stream bed was scanned for the presence of any crayfish on the open gravel / silt or on the tops or sides of cobble, boulders or vegetation.
All captured crayfish, with the exception of recently moulted individuals which were immediately returned due to their vulnerability, were immediately separated into those individuals that were those collected from under or within refugia (i.e. flint / cobble / woody debris) and those from exposed locations (i.e. open gravel and sands or on top of flints, cobbles or woody debris). Those individuals collected from exposed locations were considered to be demonstrating anomalous behaviour. The location (refugia or exposed) of individuals that were returned (i.e. recently moulted) or that managed to evade capture (noted as escapees) was recorded and juvenile or adult status was estimated. The level of expression of the anomalous behaviour was calculated by:
CA = (IE / (IE + IR)) × 100
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where CA is the percentage of recorded crayfish expressing the anomalous behaviour, IE the number of individuals recorded from exposed locations, and IR the number of individuals associated with refugia.
Figure 6.3: Manual searching on the Candover Stream at the Lower Fobdown survey section.
Whilst distinguishing sheltering from exposed individuals was usually clear, there were instances when this distinction could be considered ambiguous (i.e. a crayfish hunkered down on the outer edge, or in a depression on the surface, of a refugia), and the surveyor was required to make an objective assessment. To avoid this ambiguity influencing the relative percentage measures used for comparison, the same surveyor (Dr Rushbrook) was used for all manual surveying on the Candover Stream.
Following the thirty minute manual survey period, the two sets of crayfish were immediately transferred to the riverbank and the following information was recorded for each individual: sex, carapace length, presence of physical damage, evidence of disease, breeding condition, and moult stage (Table 6.1). Crayfish were then carefully returned to suitable areas of the stream (i.e. areas of lower flow, vegetated margins or associated with suitable refugia) along the length of the surveyed stretch.
Table 6.1: Information collected from captured crayfish.
Characterisitc Information Record
Sex Male, female or juvenile [<25mm]
Measured from tip of rostrum to the dorsal junction between carapace and Carapace Length (mm) abdomen Missing / regenerating limbs, antenna or uropods; punctures in or loss of Damage sections of carapace; missing abdominal segments
Disease Presence of burn spot, porcelain disease, etc
Breeding Status Presence of glair in females; berried [egg bearing] females
Moult Stage Pre-moult, moult, inter-moult, post-moult
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Baseline Monitoring Baseline levels of the expression of anomalous behaviour were required to be able to monitor whether the operation of the Candover Stream scheme was increasing the level of expression within the Upper Fobdown Farm site (i.e. criteria 1) or the extent of its expression within the Candover Stream (i.e. criteria 2). Following the initial observation of anomalous behaviour (5th September), and during the postponement in the operation of the scheme, two baseline manual surveys were undertaken at both the Upper and Lower Fobdown Farm sites on the 14th and 16th September. The percentage level of anomalous behaviour expression (CA) was calculated for each survey and the mean baseline CA was calculated for each site.
A total of 19 (from 51) and 23 (from 52) individuals were recorded from exposed areas during baseline surveys at the Upper Fobdown site (Table 6.2), with baseline mean CA for the Upper Fobdown population (CA [upper]) calculated at 40.8%. To allow for intrinsic variability between surveys, an increase of CA up to 20% above the baseline mean was agreed to be an acceptable degree of change and the threshold level of CA [upper] = 49% was determined (see Appendix 3 for detail of calculation). Exceeding this threshold value would suggest a significant worsening in condition of an already stressed population and the operation of the scheme would be suspended.
Fewer crayfish were recorded at the Lower Fobdown site during baseline surveys and no crayfish were recorded from exposed areas (Table 6.2). However, a threshold value of 0% was considered unsatisfactory as it would not provide any flexibility (i.e. for individuals disturbed during the survey or moving between refugia) and was therefore not considered to be a sensible value to monitor criteria 2. Therefore, a threshold level of CA [lower] = 20% from a minimum sample size of ten individuals was determined to provide a robust and pragmatic threshold level. Exceeding this threshold would provide a significant indication of a previously undetected level of stress at this monitoring site and the operation of the scheme would be suspended.
Table 6.2: Total numbers and the proportion of crayfish collected from exposed areas during crayfish behaviour surveys on the Candover Stream at the Upper and Lower Fobdown sites Flow Upper Fobdown Lower Fobdown Date Regime Total Recorded Total % Exposed Total Recorded Total % Exposed 14/09/2011 1 51 37.25 22 0.00 16/09/2011 1 52 44.23 18 0.00 20/09/2011 2 81 38.27 17 0.00 23/09/2011 2 41 29.27 20 0.00 24/09/2011 2 35 20.00 14 0.00 28/09/2011 2 54 37.04 15 0.00 30/09/2011 3 46 39.13 12 8.33* 02/10/2011 3 40 35.00 17 0.00 05/10/2011 3 51 37.25 15 0.00 07/10/2011 3 43 41.86 15 13.33 14/10/2011 3 38 31.58 13 0.00 21/10/2011 3 34 20.59 11 9.09* 26/10/2011 2 31 16.13 8 0.00 * Represents a single individual observed in exposed locations
Augmentation Monitoring It was determined that crayfish anomalous behaviour monitoring could not be undertaken on the same day as the drift net surveys. This was a consequence of the relatively small size of the Candover Stream and the disruptive nature of manual searching, which could influence the results of the drift monitoring by mobilising benthic invertebrates. Where possible, crayfish specific surveys were undertaken
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within a day of the drift net surveys, but with additional crayfish surveys undertaken during the ramp-up stage of operation (Table 6.2; Figure 5.3).
6.2.2. Statistical Analysis Each of the three crayfish behaviour monitoring sites was analysed individually. This was to reflect the unique objectives associated with the monitoring of each site (see section 6.1), the resulting variation in survey method, and depth and type of statistical testing required. Where appropriate, and prior to more detailed analysis, data was tested to ensure it conformed to the assumptions associated with parametric testing. All continuous variable data was tested for normal distribution using the Anderson- Darling test. Data that deviated from normal distribution was first Log10- or arcsine square-root transformed (as appropriate) to normalise variance and subsequently tested using parametric tests. Discrete or small sets of data that could not be normalised were tested using non-parametric equivalents, with all results from non- parametric testing adjusted for ties as appropriate. All samples were tested using Minitab® 14.0.
Upper Fobdown A Kruskal-Wallis test was performed to test for an effect of flow regime on the level of expression of anomalous behaviour (CA[Upper]), with subsequent Spearman’s rank correlations undertaken to test for an effect of flow rate and survey day on both CA[Upper] and total numbers of crayfish recorded. For all captured individuals (excluding those moulting), a Scheirer-Ray-Hare test (non-parametric equivalent to the two-way ANOVA; Dytham, 2011) was performed to test the effects of life stage (adult vs. juvenile) and the expression of anomalous behaviour (refugia vs. exposed) on carapace length; subsequent Mann-Whitney U tests were performed to undertake pair-wise analysis as required. A second Scheirer-Ray-Hare test was performed to test the effects of adult sex (male vs. female) and the expression of anomalous behaviour on carapace length; subsequent Mann-Whitney U tests were performed to undertake pair-wise analysis as required. Spearman’s rank correlation tests were performed to test for an effect of survey day on carapace length for exposed and refugia groups.
Chi-square tests of association were performed on the expression of anomalous behaviour with the following; life-stage, sex within adults, development of female sexual condition, presence of porcelains disease, presence of damage and presence of burn spot.
Lower Fobdown A Kruskal-Wallis test was performed to test for an effect of flow regime on the level of expression of anomalous behaviour (CA[Lower]), with subsequent Spearman’s rank correlations undertaken to test for an effect of flow rate and survey day on both CA[Lower] and total numbers of crayfish recorded.
6.3. Methodology – River Alre No anomalous behaviour was observed in the white-clawed crayfish during an investigatory survey at Drove Lane on the River Alre. Nonetheless, to ensure the River Alre sub-population continued to show no evidence of this anomalous behaviour, it was considered necessary to undertake low-level monitoring of this population as a precaution (criteria 3).
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6.3.1. Manual Searches A twenty minute manual survey was undertaken by Dr Kerry Evans (with one exception) immediately prior to each of the scheduled River Alre drift net surveys (Figure 6.4). This time was evenly divided between immediately above and below the road bridge at Drove Lane. The final two minutes of the latter were spent investigating areas of limited river bed heterogeneity, where crayfish would have been able to avoid high flows (during augmentation) and the expression of anomalous behaviour would be observed more readily. All observed crayfish were recorded as either exposed or associated with refugia, but no individuals were captured. These values were used to calculate values of CA [Drove] in order to monitor whether the River Alre sub-population began to express the anomalous behaviour seen on the Candover Stream.
Figure 6.4: Manual searching for white-clawed crayfish on the River Alre, immediately upstream of Drove Lane.
Baseline Since no anomalous behaviour had been observed within the River Alre sub- population, the River Alre flow augmentation scheme was commenced prior to any crayfish specific surveys being undertaken; the baseline values were in fact determined using the mean of the values of CA calculated from the day that pump 1 (13th September) and pump 2 (15th September) were switched on respectively.
No crayfish (from 6) and a single (from 16) individual were recorded from exposed areas during baseline surveys at the Drove Lane site (Table 6.3), with ‘baseline’ mean CA for Drove Lane (CA[Drove]) calculated at 4.54%. Even applying the same principle as for Upper Fobdown, this would equate to a threshold value of 5.45% (see Appendix 3 for detail of calculation).This value was considered unsatisfactory as it did not provide sufficient flexibility (i.e. for individuals disturbed during the survey or moving between refugia) and could therefore not be considered a sensible value to infer a potential impact of the River Alre scheme. In keeping with the Lower Fobdown site, a threshold level of CA[Drove] = 20% from a minimum sample size of ten individuals was determined to provide a robust and pragmatic threshold level. Exceeding this threshold would provide a significant indication of a previously undetected level of stress at this monitoring site, and the operation of the scheme would be suspended.
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Augmentation Monitoring It was considered that performing manual surveys on the same day as the planned drift net surveys would not affect the drift net results and were therefore undertaken immediately prior to the deployment of the nets (Table 6.3). This was a reflection of the substantially greater size of the River Alre, and the fact that the drift net survey site was approximately 65m downstream of Drove Lane.
Table 6.3: Total number and percentage of crayfish collected from exposed areas during crayfish behaviour surveys on the River Alre at Drove Lane. Drove Lane Date Flow Regime Total Recorded Total % Exposed 13/09/2011 2 6 0.00 15/09/2011 2 16 6.25* 19/09/2011 2 12 8.33* 22/09/2011 2 21 14.29 29/09/2011 2 14 0.00 03/10/2011 3 11 0.00 06/10/2011 3 8 0.00 13/10/2011 3 10 10.00* 20/10/2011 3 3 33.33* 27/10/2011 2 9 11.11* * Represents a single individual observed in exposed locations
6.3.2. Statistical Analysis Spearman’s rank correlations were performed to test for an effect of flow rate and survey day on CA[Drove], and a Pearson’s correlation to test for an effect of flow rate and survey day on the total numbers of crayfish recorded.
6.4. Results – Candover Stream
6.4.1. Upper Fobdown A total of 597 (refugia = 392 vs. exposed = 205) crayfish were recorded during 13 surveys (Table 6.2). Crayfish numbers per survey (or CrPUE) were consistently greater than the numbers recorded at the same location during long-term monitoring of Fobdown Farm between 1997 and 2008 (Hutchings, 2009).
Of the 597 crayfish recorded during the 13 surveys, 455 (refugia = 271 vs. exposed = 184) were successfully captured. This equates to a total capture success rate of 76.2%, and capture success rates of 69.1% and 89.8% for individuals associated with refugia and exposed locations respectively. These capture success rates are consistent with results from long-term monitoring of this location (Hutchings, 2009). However, juveniles comprised a substantial component of total and refugia escapees, but not for exposed locations (adults:juveniles; [total] 39:103, [refugia] 28:93; [exposed] 11:10).
A total of two captured individuals (1 vs.1) were moulting at the time of capture and were not subject to more detailed analysis. Therefore, based on 453 individuals, mean (± one standard deviation) and median (inter-quartile range) carapace lengths at the Upper Fobdown site were 26.5mm (±8.0mm) and 28.1mm (20.6mm – 31.4mm) respectively. Mean male to female ratio across the study was 1:1.18, but ratios
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fluctuated throughout the study, ranging from almost half as many females as males to more than double (Table 6.4).
Table 6.4: Sex ratio of females per male for individual crayfish surveys at Upper Fobdown. Survey No. 12345678910111213 Sex Ratio 0.811.460.91 1.3 0.64 1.89 0.92 2.17 1.5 1.43 1.75 0.75 -
Flow regime There was no significant difference in the levels of CA[Upper] between flow regimes (Kruskal-Wallis: H = 3.59, d.f. = 2, p = 0.167). However, comparisons of the median and interquartile ranges of CA[Upper] for each regime, indicates that levels were reduced during the operation of the Candover Stream scheme when compared to baseline levels, and this was particularly notable during flow regime 2 (Figure 6.5). This non- significant trend is retained if data for the ramp-down period is removed from analysis (i.e. from regime 2), though the reduction is less notable (median values: regime 1 = 40.7%; regime 2 = 33.2%; regime 3 = 36.1%). Furthermore, there was no correlation between flow rate and the level of CA[Upper] (Spearman’s rank correlation: rs = 0.072, N = 13, p = 0.816) nor the total number of individuals recorded (Spearman’s rank correlation: rs = -0.152, N = 13, p = 0.621).
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Expression of anomalous behaviour (%) anomalous of Expression 15 1 2 3 Flow Regime
Figure 6.5: Boxplot of the effect of flow regime on the expression of anomalous behaviour (CA[Upper]). Median values: Regime 1 = 40.7%, Regime 2 =29.3%, Regime 3 = 36.1%.
There was a highly significant negative correlation between the total number of crayfish recorded per survey (CrPUE) and survey day (Spearman’s rank correlation: rs = -0.677, N = 13, p = 0.011), but there was no correlation between survey day and CA[Upper] (Spearman’s rank correlation: rs = -0.435, N = 13, p = 0.138). However, a simple scatter-plot of the level of expression of anomalous behaviour (CA[Upper]) against time indicates that there was a general reduction in observed levels (Figure 6.6) .
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Figure 6.6: Scatter-plot showing the expression of anomalous behaviour (CA[Upper]) against survey day.
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Figure 6.7: Boxplot of exposed vs refugia for carapace length. Median values: exposed = 30.4mm, refugia = 23.1mm).
Carapace length, life stage and sex (processed individuals only) There was a highly significant difference in carapace length between crayfish from different life stages (i.e. adults, juveniles) and between crayfish collected at exposed and refugia locations (Scheirer-Ray-Hare: [life stage] H = 252.175, d.f. = 1; p < 0.001;
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[location] H = 78.975, d.f. = 1, p < 0.001), but there was no interaction between these two factors (Scheirer-Hare-Ray: H = 0.003, d.f. = 1, p = 0.954). Crayfish collected from exposed areas were significantly larger than those collected associated with refugia (Mann-Whitney U test: W = 49149.0, n = 183,270, p = 0.001; Figure 6.7). However, there was negative correlation between carapace length and study day for both exposed (Spearman’s rank correlation: rs = -0.270, N = 183, p < 0.001) and refugia (Spearman’s rank correlation: rs = -0.278, N = 270, p < 0.001) groups.
Pairwise comparisons found juveniles were significantly smaller than both males and females (Mann-Whitney U test: [male] W = 30500.0, n = 181,147 , p < 0.001; [female] W = 37485.0, p < 0.001). Within the adult class, there remained a highly significant difference in carapace length between crayfish collected at exposed and refugia locations (Scheirer-Hare-Ray: H = 11.142, d.f. = 1, p < 0.001), but there was no significant difference between sexes and no interaction between the two factors (Scheirer-Hare-Ray: [sex] H = 0.785, d.f. = 1, p = 0.375; [interaction] H = 0.238, d.f. = 1, p = 0.635). Crayfish collected from exposed areas were significantly larger than those collected associated with refugia (Mann-Whitney U test: W = 49149.0, n = 150,122, p < 0.001; Figure 6.8).
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Figure 6.8: Boxplot of exposed vs refugia for carapace length of adults only. Medians values: exposed = 31.4mm, refugia = 30.0mm.
There was a highly significant association between the expression of anomalous behaviour and life stage (χ2 = 3.767; d.f. = 1; p < 0.001); the juvenile class was the largest contributor to this association, with significantly fewer juveniles recorded from exposed locations than would be expected (Table 6.5a). Within the adult class, there was a non-significant association between the expression of anomalous behaviour and sex (χ2 = 65.379; d.f. = 1; p = 0.052); the use of refugia was the biggest contributor to this non-significant association, with a greater number of males observed at refugia locations than would be expected (Table 6.5b).
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Table 6.5: Results of Chi-square tests of association between crayfish location and a) life stage and b) sex (adults only). a) Location Adult Juvenile Total Observed (O) 122 148 Refugia Expected (E) 162.12 107.88 270 (O-E)2/E 9.928 14.920 Observed (O) 150 33 Exposed Expected (E) 109.88 73.12 183 (O-E)2/E 14.648 22.013 Total 272 181 453
b) Location Male Female Total Observed (O) 64 58 Refugia Expected (E) 56.07 65.93 122 (O-E)2/E 1.123 0.955 Observed (O) 61 89 Exposed Expected (E) 68.93 81.07 150 (O-E)2/E 0.913 0.776 Total 125 147 272
There was no association between the development of female sexual condition (i.e. the development of the glair glands) and crayfish location (χ2 = 0.062; d.f. = 1; p = 0.803).
Presence of disease and damage (processed individuals only) A total of 22 crayfish at the Upper Fobdown survey site were observed to be infected with porcelain disease, representing 4.86% prevalence within the population. Most infected individuals were collected during the first half of the study (under flow regimes 1 and 2). However, during all surveys those individuals identified to be infected with porcelains disease constituted only a minority of all individuals collected (Figure 6.9).
Nine individuals infected with porcelain disease were collected from refugia and thirteen from exposed locations. There was a non-significant association between the identification of porcelain disease and location (χ2 = 3.356, d.f. = 1, p = 0.067); the presence of infection was the biggest contributor to this non-significant association, with a greater number of infected individuals observed at exposed locations than would be expected (Table 6.6a).
A number of crayfish exhibited evidence of external damage, with the presence of some damage recorded among 26.6% of all individuals. This damage ranged from missing or regenerating pereopods, damage to chelae or antennae and, in the most extreme cases, substantial damage to the carapace (i.e. mammalian bite marks) or missing sections of the abdomen. There was a highly significant association between the presence of damage and location of crayfish (χ2 = 15.962, d.f. = 1, p < 0.001); the location of crayfish was the biggest contributor to this association, with significantly fewer undamaged crayfish collected from exposed locations than would be expected (Table 6.6b).
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Figure 6.9: Total number (open bars) and the number of porcelain infected (shaded bars) crayfish collected on each of the 13 surveys undertaken at Upper Fobdown.
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Table 6.6: The results of Chi-square tests of association between crayfish location and a) infection with porcelain disease, the b) presence of external damage and the c) presence of burn spot. a) Location Infected Uninfected Total Observed (O) 9261 Refugia Expected (E) 13.11 256.89 270 (O-E)2/E 1.290 0.066 Observed (O) 13 170 Exposed Expected (E) 8.89 174.11 183 (O-E)2/E 1.903 0.097 Total 272 181 453
b) Location Presence Absence Total Observed (O) 138 132 Refugia Expected (E) 158.54 111.46 270 (O-E)2/E 2.662 3.786 Observed (O) 128 55 Exposed Expected (E) 107.46 75.54 183 (O-E)2/E 3.927 5.586 Total 266 187 453
c) Location Presence Absence Total Observed (O) 53 217 Refugia Expected (E) 72.12 197.88 270 (O-E)2/E 5.069 1.847 Observed (O) 68 115 Exposed Expected (E) 48.88 134.12 183 (O-E)2/E 7.478 2.726
Total 121 332 453
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Burn spot is often associated with external damage, and a highly significant association was also recorded between the presence of burn spot and the location of crayfish (χ2 = 17.120, d.f. = 1, p < 0.001); the presence of burn spot was the biggest contributor to this association, with significantly more crayfish from exposed locations infected with burn spot than would be expected (Table 6.6c).
6.4.2. Lower Fobdown A total of 197 (refugia = 193 vs. exposed = 4) crayfish were recorded during 13 surveys (Table 6.2). Crayfish numbers per survey (or CrPUE) were consistent with the numbers recorded at the same location during long-term monitoring of Fobdown Farm between 1997 and 2008 (Hutchings, 2009).
Of the 197 crayfish recorded during the 13 surveys, 133 (refugia = 129 vs. exposed = 4) were successfully captured. This equates to a total capture success rate of 67.5%, and capture success rates of 66.8% and 100% for individuals associated with refugia and exposed locations respectively.
A total of five captured individuals (all associated with refugia) were moulting at the time of capture and were not subject to more detailed analysis. Therefore, based on 128 individuals, mean (± one standard deviation) and median (inter-quartile range) carapace lengths at the Lower Fobdown site were 20.6mm (±6.1mm) and 20.6mm (18.5-23.1mm) respectively. Furthermore, crayfish recorded at the Lower Fobdown site were significantly smaller than crayfish collected at refugia locations at the Upper Fobdown site (Mann-Whitney U Test: W = 21361.0, N128,270, p < 0.001).
Effect of flow regime The principal aim of the crayfish behavioural monitoring at the Lower Fobdown site was to ensure that the Candover Stream scheme was not acting as a vector for the increase of downstream expression of this anomalous behaviour (criteria 2). There was no significant difference in the level of CA[Lower] recorded between flow regimes (Kruskal-Wallis [adjusted for ties]: H = 4.12, d.f = 2, p = 0.128). Furthermore, there was no correlation between flow rate and the level of CA[Lower] (Spearman’s rank correlation: rs = 0.486, N = 13, p = 0.092) nor between flow rate and the total number of individuals per survey (CrPUE) recorded (Spearman’s rank correlation: rs = -0.397, N = 13, p = 0.180). There was a highly significant negative correlation between the total number of crayfish recorded and survey day (Spearman’s rank correlation: rs = - 0.816, N = 13, p = 0.001), but there was no correlation between survey day and CA[Lower] (Spearman’s rank correlation: rs =0 .409, N = 13, p = 0.166).
Insufficient numbers of crayfish were observed / collected from exposed areas during surveys of the Lower Fobdown site to enable a meaningful comparison of the two groups. Therefore, no further analysis was undertaken of the data collected at this site, though it was observed that no individuals were identified to be infected with porcelain disease from either refugia or exposed locations.
6.5. Results – River Alre The single aim of the crayfish behavioural monitoring on the River Alre was to ensure that there continued to be no evidence for the expression of anomalous behaviour (above the threshold level) at Drove Lane (criteria 3). Though the threshold level was exceeded on one occasion (Table 6.3), this was associated with a very small sample size where only a single individual was recorded in exposed areas. This was therefore below the pre-agreed sample size (see Appendix 3) to make a pragmatic and robust decision to suspend the operation of the River Alre flow augmentation scheme.
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There was no correlation between flow rate and the level of CA[Drove] (Spearman’s rank correlation: rs =-0.450, N = 10, p = 0.192) nor between flow rate and the total number of individuals recorded (Pearson’s correlation: r = -0.329, N = 10, p = 0.353). There was also no correlation between survey day and the total number of crayfish (Pearson’s correlation: r = -0.475, N= 10, p = 0.165) nor between survey day and the level of CA[Drove] (Spearman’s rank correlation: rs = 0.438, N = 10, p = 0.206).
As it was not considered that the crayfish observed at Drove Lane were expressing anomalous behaviour, no further analysis was undertaken of the data collected at this site.
6.6. Discussion
6.6.1. Effects of the Upper Itchen Flow Augmentation Schemes Throughout the operation of the Candover Stream flow augmentation scheme, a notable proportion of the white-clawed crayfish at the Upper Fobdown survey site continued to demonstrate anomalous diurnal behaviour. There was no increase in the level of expression of this behaviour associated with the onset of the scheme, and no significant difference in the level of expression as a result of different flow regimes (baseline, ramp-up/crank-down, full-output). However, when compared to baseline levels, there was a non-significant reduction in the levels of anomalous behaviour during flow regimes associated with the operation of the scheme, most evident during flow regime 2 (ramp-up / down). There was no correlation between the level of expression and flow rate, nor was there significant correlation between the level of expression and the duration of the study (i.e. survey day). Nonetheless, fewer crayfish were recorded per survey at both Fobdown sites as the scheme progressed. It is therefore considered that there was no discernable effect of the augmentation scheme on the expression of anomalous crayfish behaviour at the Upper Fobdown site.
A small number of individuals were recorded actively moving through exposed locations at the Lower Fobdown site, though the majority of surveys recorded no such behaviour. It is not exceptional for a very small number of white-clawed crayfish to be observed in exposed locations within such an extensive survey period (Rushbrook, personal observation), as crayfish can be disturbed or missed during ‘stone turning’ and observed as they move away. However, this would usually equate to two or three individuals during four or five surveys, and not the levels observed at the Upper Fobdown site. Therefore, there was no evidence to suggest that the expression of the anomalous crayfish behaviour was extending downstream with the operation of the Candover Stream flow augmentation scheme.
One or more crayfish were recorded in exposed locations on over half the surveys at Drove Lane. However, with the exception of one occasion where the total catch was three individuals, the percentage of individuals observed in exposed locations remained low. Furthermore, excluding this exception, levels were considerably lower than the level of expression of anomalous behaviour that had trigger concerns at the Upper Fobdown site. Therefore, there was no evidence from this study to indicate that the expression of the anomalous behaviour was present within the River Alre.
6.6.2. Consequences and Potential Causes of the Anomalous Behaviour
The expression of anomalous diurnal behaviour in white-clawed crayfish, as observed at the Upper Fobdown survey location, is a classic sign of infection with A.astaci ([crayfish plague] Oidtmann, 2000; Evans & Edgerton, 2002). However, testing for the
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presence of this pathogen at Fobdown proved negative. Furthermore, through this detailed two month study, no mass mortalities occurred and only four dead crayfish were recorded. When compared with the 597 living individuals recorded at this site during the study, this is considered well within natural levels. Furthermore, no individuals were observed moving out of the river onto the river banks and, with the exception of this diurnal anomalous behaviour and the presence of porcelain disease (discussed later in this section), very few individuals showed signs of being highly stressed or in poor health (i.e. unable to right themselves if on their back).
Although a number of unexplained mass mortalities of crayfish have been documented where crayfish plague could be reliably ruled out (Edgerton et al., 2002a; Holdich & Jackson, 2010; Stebbings, personal communication), very few examples exist where high numbers of white-clawed crayfish have been recorded displaying similar anomalous behaviour in their natural environment without associated mortality (exceptions: Frayling, personal communication; Peay, personal communication). Therefore, determining both the consequences and cause of this behaviour is essential in planning and delivering conservation measures for what is an already highly vulnerable population.
Within this study, there were a number of significant differences between those individuals captured in association with refugia and those at exposed locations. Crayfish collected from exposed locations were significantly larger than those associated with refugia. This was largely a consequence of the far fewer juveniles recorded in exposed locations, and this result is in spite of the larger numbers of juvenile escapees associated with the refugia than exposed locations. However, when testing the adults independently, this relationship between carapace length and locations was retained, with those individuals associated with refugia on average smaller than those in exposed areas. However, crayfish location was not wholly determined by size, and the two largest individuals were both recorded under large rocks / small boulders. The carapace length of the adult crayfish captured did not differ between the sexes nor was there an association between the presence of well developed glair glands (indicating a female’s propensity to breed; Reynolds, 2002) and location in females, though there was a non-significant association between males and the occupation of refugia.
Crayfish from exposed locations were more likely to possess injuries attributed to agonistic interactions and / or an escape from a predator including the loss of limbs, damage to the carapace and the presence of burn spot (Holdich, 2002; Sáez-Royuela et al., 2002; Oidtmann, 2000). Furthermore, there was a non-significant association between individuals infected with porcelain disease and exposed locations.
Crayfish numbers per survey (or CrPUE) at the Upper Fobdown survey site were consistently higher than the numbers recorded at the same location (with the same level of survey effort) during long-term monitoring of Fobdown Farm between 1997 and 2008 (Hutchings, 2009). In fact, all CrPUE values recorded during this study exceeded the maximum number of crayfish recorded at any location during the earlier study. Although comparisons between these two studies must be assessed with caution, as each was undertaken at opposite ends of the recommended survey period (July – October), it is considered potentially significant that greater numbers were always returned during this study, even from those surveys undertaken outside the optimum survey period (i.e. in October; Peay, 2003). It is considered likely that the increased ease of locating and subsequent capture of individuals from exposed locations would be an important factor in this result. Though care was taken by the surveyor to attribute similar levels of survey effort to exposed and refugia locations, exposed individuals could be observed from a greater distance and were significantly
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easier to capture. This was considered to be a consequence of the fact that time was not required to carefully ‘turn’ and place stones (or other refugia) before capture of exposed individuals could be attempted, providing less of an opportunity for the crayfish to escape, rather than a consistent difference in the responsiveness of the individuals from these two locations. As the surveyor(s) in the original study would solely be searching for crayfish associated with refugia, it is likely that the total number recorded would therefore be lower. Furthermore, for those individuals successfully captured, there was greater consistency between the two studies in sex ratios, with a general tendency for a slightly higher number of females despite the considerable variation between surveys in the actual sex ratios returned.
An alternative explanation is that the greater numbers captured does represent an actual increase in crayfish density at the site, and that the expression of this anomalous behaviour (and associated greater ease of capture) is in fact a consequence of a rapid increase in population size and resulting competition for refugia. Refugia availability is an important factor in determining abundance and densities of white-clawed crayfish (Broquet et al., 2002, Gherardi, 2002, Nyström, 2002, Hutchings, 2009). The tendency for larger individuals to be recorded expressing anomalous behaviour may therefore reflect a shortage of refugia of a suitable size, since studies have shown that crayfish and refugia sizes are positively correlated (Foster, 1993). As crayfish directly compete with each other for suitable refugia, an increase in crayfish numbers to a level above the carrying or resource (refugia) capacity of the site could result in an increase in agonistic interactions (Nystr m, 2002). The losers would therefore be excluded and forced into sub-optimal habitat such as more exposed or open locations, and may display evidence of these encounters such as damaged chela (claw) or antenna (Holdich, 2002, Sáez-Royuela et al., 2002). Furthermore, individuals excluded from shelters are at a greater risk to predators, increasing the likelihood of displaying such injuries (Gherardi, 2002). This expected increase in the presence of injuries in exposed individuals is consistent with the findings of this study, with injuries both consistent with agonistic interactions and predation attempts recorded (Figure 6.10). However, during all thirteen surveys a notable proportion of the suitable refugia investigated were not sheltering crayfish.
Crayfish size, refugia type and refugia dimensions are important factors in determining refugia selection in Austropotamobius spp. ([white-clawed crayfish]: Foster, 1993; Demers et al., 2003; [stone crayfish]: Streissl & Hödl, 2002), and differences in the availability of certain refugia type(s) may effect an age / size specific class. However, it is considered that there were unutilised refugia available for all size classes and the significantly larger average size of crayfish from exposed locations is not a consequence of a shortage of size-suitable refugia for mature adults; although the potential influence of other factors to create sub-optimal conditions at these unutilised refugia (e.g. associated localised flow rates, orientation, etc) cannot be discounted. Therefore, it is considered that insufficient evidence exists to support the theory that the expression of anomalous behaviour within the Upper Fobdown site is a consequence of an increase in crayfish density and associated increased competition for resources (i.e. refugia availability).
A number of abiotic factors are known to influence crayfish behaviour, with their influence on daily and seasonal patterns well documented (Gherardi, 2002). However, at uncharacteristically elevated or reduced levels, abiotic factors can act as environmental stressors with impacts on crayfish behaviour and mortality. The first observation of anomalous behaviour at Upper Fobdown was associated with an extended low flow period, immediately prior to the testing of the Candover Stream scheme, and was proposed as a potential cause for its expression. Water levels within the Candover Stream were likely to be lower than would be characteristic of that time
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of year, resulting in the loss of the marginal habitat that is utilised by juvenile crayfish (Demers et al., 2003; Hutchings, 2009). However, as previously discussed juvenile crayfish were significantly under-represented within those individuals recorded at exposed locations. Furthermore, the operation of the flow augmentation scheme resulted in the re-availability of these microhabitats, and should have resulted in a significant reduction if not disappearance of the anomalous behaviour.
Figure 6.10: White-clawed crayfish captured at Upper Fobdown with injuries consistent with mammalian bite marks: puncture wounds to carapace and abdomen and section of carapace lost on its right flank.
An increase in temperature and resulting reduction in levels of dissolved oxygen is often associated with a reduction in water flow and correlated reduced water depths. Crayfish species demonstrate a number of behavioural adaptations to low oxygen levels including exposing their gills to the air-water interface and crawling onto land (Taylor & Wheatly, 1980; Nyström, 2002 and references therein). Maximum daytime water temperatures at Upper Fobdown reached in excess of 18-19°C in the days immediately prior to the discovery of this anomalous behaviour, and had reached over 22°C in early August. However, despite the considerable decline in water temperature over the duration of the study period, the expression of the anomalous behaviour was retained. Furthermore, levels of dissolved oxygen and biological oxygen demand (based on water quality and in-situ measurements) recorded throughout September and October remained consistently within acceptable levels. Furthermore, no crayfish were observed at the water’s surface or crawling onto the land. It is therefore considered that reductions in water levels / flow, temperature or oxygen levels were not the cause of the observed anomalous crayfish behaviour.
White-clawed crayfish are susceptible to a number of organic and inorganic pollutants (Nyström, 2002 and references therein), and extreme pollution events have resulted in the loss or fragmentation of a number of UK white-clawed crayfish populations
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(Holdich & Reeve, 1991; Peay, 2010; Rogers & Watson, 2010). Most sub-lethal behavioural studies associated with organic pollution have focused on the response of crayfish to the associated reduction in oxygen levels, which as outlined above was not a trend observed within this study. In fact, there is increasing evidence that crayfish of the genus Austropotamobius are quite tolerant to a decrease in the partial pressure of ambient oxygen and thus this specific effect of eutrophication or organic pollution. Water quality testing at Abbotstone Causeway (approximately 1.1km upstream of the Upper Fobdown survey site) recorded levels of ammonia, soluble reactive phosphorus and suspended solids within the required standards for water quality and that were consistent with the previous year. Furthermore, though inorganic pollutants such as heavy metals were not included in this analysis, it is highly unlikely that such pollutants would be sufficiently diluted for the Lower Fobdown site not to express the anomalous behaviour. It is therefore considered that there is no evidence that an acute or chronic pollution event was the cause of the anomalous crayfish behaviour.
White-clawed crayfish are susceptible to a wide range of pathogens and parasites (Edgerton et al., 2002b; Evans & Edgerton, 2002), many of which cause symptoms consistent with the anomalous behaviour observed at the Upper Fobdown site. Initial discussions following the discovery of the observed anomalous behaviour identified infection with Thelohania contejeani (porcelain disease) as a potential causal factor. Crayfish infected with Thelohania spp. become lethargic and anorexic as the disease progresses and the parasite replaces the host‘s muscle tissue. This could result in individuals being more likely to be observed away from refugia as the disease develops, with heavily infected individuals more likely to be found out in the open than less heavily infected ones (Stebbings, personal communication; but see Imhoff et al., 2009). Furthermore, the death of diseased individuals and the associated ‘loss’ (through downstream drift / predation) of these individuals could explain the non- significant trend for a reduced level of expression of anomalous behaviour with the duration of the monitoring, and the reduction in CrPUE at both Upper and Lower Fobdown across the survey visits. However, although there was a non-significant association between crayfish infected with T. contejeani and expression of anomalous behaviour, the numbers of visibly (i.e. heavily) infected individuals was considerably lower than the number of individuals expressing anomalous behaviour. In addition, despite greater levels of infection than recorded in previous monitoring visits in July (Hutchings, 2009), the actual difference in percentage infections was moderate (3.3% refugia vs. 7.1% exposed), and even the upper value is well within naturally recorded levels at other populations (Holdich, 2003). Therefore, there is not strong evidence to support the theory that T. contejeani is the cause of the anomalous behaviour, though it is important to emphasise that proper investigation of this possible cause could not be undertaken within the design of this study.
Two further explanations of the anomalous behaviour considered were the possibility that low light levels, a result of tree-cover, encouraged crayfish to forage; and that the behaviour represents the onset of mate-searching behaviour. Dense tree cover is present at the Upper Fobdown site, but light levels were never considered to be particularly low and were not considered to be lower than in recent years. However, with the very low flows at the time of discovery, it was suggested that a combination of low flows and light levels coupled with the indicated high population density may have triggered a localised change in population behaviour. However, if it was the cause of the anomalous behaviour, its expression should have disappeared with the onset of the flow augmentation scheme and the evident increase in light levels by mid-late September as the trees shed their leaves. It is therefore considered that the expression of anomalous behaviour within the Upper Fobdown site was not a consequence of dense tree cover and associated low light levels at the site.
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Exposed individuals were on average larger than those recorded associated with refugia and are likely to constitute an important component of the breeding ‘population’ at the Upper Fobdown site. However, timing for the onset of mating in Britain is determined by photoperiod (day length) and water temperatures dropping below 10-11°C for extended periods (Reynolds, 2002; Holdich, 2003). The latter is completely inconsistent with the situation at the time of discovery of the anomalous behaviour, with water temperatures elevated by the warm early autumn ambient temperatures and exacerbated by the low flow conditions. Furthermore, there was no evidence that the anomalous behaviour represents males actively seeking out females, there was no difference in the development of glair glands in females between locations and, although only low numbers were recorded, the presence of juveniles associated with exposed groups and their increase in relative abundance as the study progressed, all contradicts this theory. It is therefore considered that the expression of anomalous behaviour within the Upper Fobdown site is not a consequence of an early onset of mating behaviour.
6.6.3. Lower Fobdown and the ‘absence’ of anomalous behaviour Although it was considered important to limit cross-comparisons between sites, it is immediately evident that far fewer and significantly smaller crayfish were collected at Lower Fobdown compared with the Upper Fobdown site; with crayfish at the Lower Fobdown site smaller on average than crayfish associated with refugia in the Upper site. There is considerably less suitable habitat for crayfish at the Lower Fobdown site and crayfish numbers per survey were consistent with the numbers recorded at the same location during long-term monitoring of Fobdown Farm between 1997 and 2008 (Hutchings, 2009). Therefore, the differences between the two sites in the total number of crayfish recorded may be a consequence of habitat availability, accentuated by the potentially skewed numbers of crayfish recorded in the Upper Fobdown site as discussed above. Furthermore, the possibility that regular fluctuations or cyclical patterns in the adult and juvenile cohorts exist at this site has been hypothesised in previous studies (Hutchings, 2009). However, the latter would not explain the observed differences between the two sample sites as a good size / age class range was recorded at Upper Fobdown.
An increased level of predation pressure may explain the differences in size and numbers between the two Fobdown survey sites. An active otter Lutra lutra holt is located immediately downstream of the Lower Fobdown survey site, and crayfish remains were discovered within otter spraint at the holt’s entrance on a number of occasions (Rushbrook & Selby, personal observations). Though it is likely that the otter(s) is foraging within both sites, the inferior habitat complexity and quality and associated reduced water turbidity at the Lower Fobdown site would result in a greater susceptibility to predation of individuals present there. Otters will preferentially feed on larger crayfish and could cause the skew in size / age class distribution observed at the Lower Fobdown site. Furthermore, and of greater significance with respect to this study, this may also obscure the expression of the anomalous behaviour within this site, as any crayfish spending extensive amounts of time in exposed locations during crepuscular (dawn / dusk) periods may be highly susceptible to predation and could effectively be removed from detection during surveys. Therefore, though the reduction of CrPUE at Lower Fobdown over the duration of the study could simply reflect natural changes in crayfish behaviour, it could alternatively reflect a steady loss of individuals either through unrecorded drift or unrecorded predation. However, the former is not supported by other results (see section 5.2.1) and the latter cannot be tested within the design of this experiment.
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7. CONCLUSIONS AND RECOMMENDATIONS
7.1. Summary
7.1.1. Ecological Monitoring The operation of the Candover Stream and River Alre flow augmentation schemes resulted in immediate and significant modifications in flow rates and water levels at two locations of regional importance for the internationally endangered white-clawed crayfish. Specifically, flow rates on the Candover Stream during the augmented period were significantly greater than seven of the past eleven years and were therefore not comparable with typical summer flows. However, the River Itchen Site Action Plan proposes that these schemes would only be used to support the target flow regime for the River Itchen, and would therefore only be used in exceptionally low flow conditions such as during the severe drought of 1976. The threshold low flow conditions required for their operation was not reached prior to testing, and therefore these schemes would not have been operationally required in 2011. Conclusions drawn from the test carried out in 2011 should therefore be considered in this context.
Studies from other sites have demonstrated that a naturally or artificially induced rapid or significant increase in flow rates can result in increased levels of passive or catastrophic drift of benthic macroinvertebrates, including white-clawed crayfish. During operation of the Upper Itchen flow augmentation schemes, no such increase in drift of white-clawed crayfish was recorded. However, it is considered very plausible that an unrecorded increase in the levels of crayfish drift may have occurred. Furthermore, as the operation of the scheme progressed, concurrent behavioural monitoring identified a reduction in the total numbers of crayfish being recorded per survey at each of the Fobdown survey sites. This could represent individuals being lost from these sites through drift, or could simply represent natural changes in crayfish numbers or activity.
No consistent relationships between flow rates and taxon specific macroinvertebrate groups were identified during the drift net studies, and no effect of the scheme was recorded on the community of drifting target organisms nor the wider benthic macroinvertebrate community. These findings suggest that there was no effect of the augmentation scheme on the invertebrate community per se, nor an indirect effect on white-clawed crayfish through the loss of important prey items. However, it is important to acknowledge that the findings from the wider benthic macroinvertebrate community study are based on the results of a single pre- and post-augmentation sample.
A significant negative correlation between flow rates and maximum daytime water temperatures was observed on the Candover Stream, with water temperatures also significantly influenced by ambient temperatures, but overnight water temperature unaffected by flow. The observed reduction in the maximum daytime water temperatures recorded within the marginal zone could have significant negative effects on juvenile moult and therefore growth patterns. Juvenile growth patterns were not monitored as part of this study, but it is considered likely that growth rates would be inhibited by these reduced maximum daytime water temperatures, with associated implications for individual survival rates in the short term, and on recruitment to the sub-population in the long-term.
There was no apparent effect of the operation of the Candover Stream flow augmentation scheme on water quality downstream of the Grange Lake. Determining
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the relationships between water quality and the operation of the River Alre flow augmentation scheme is less straightforward, as significant fluctuations in levels of a number of variables (i.e. phosphate, ammonia) are regularly recorded. However, there was no apparent effect from the operation of the scheme on water quality downstream of the Soke.
7.1.2. Anomalous Crayfish Behaviour Monitoring Throughout the operation of the Candover Stream scheme, a notable proportion of the white-clawed crayfish at the Upper Fobdown survey site continued to demonstrate anomalous behaviour. There was no significant correlation between the level of expression of this behaviour with flow rate or with the duration of the monitoring (i.e. survey day). There was no significant effect of flow regime on the expression of anomalous behaviour, though a potential difference between baseline and operating flow regimes was returned.
It is considered that, although a small number of individuals were observed in exposed locations at Lower Fobdown and Drove Lane, this is likely to simply reflect the high level of survey effort, and there was no evidence to indicate the expression of anomalous behaviour at either of these sites. However, the reduced number and significantly smaller size of crayfish at the Lower Fobdown site, when compared with the Upper Fobdown site less than 650m upstream, dictates that the potential for confounding factors (e.g. increased levels of predation) to conceal the expression of this behaviour cannot be discounted.
At Upper Fobdown, crayfish expressing anomalous behaviour were significantly larger, under-represented by juvenile cohorts and were more likely to present signs of injury and associated disease (i.e. burn spot). A number of potential causes of this diurnal behaviour were considered including disease (crayfish plague and porcelain disease), crayfish density / refugia availability, water levels, water temperature, dissolved oxygen levels, pollution, overhead light levels, sex and propensity to breed (see section 6.6.2. for details). However, none of these factors provide a robust or definitive explanation for the expression of this anomalous behaviour.
7.2. Ecological Cost-Benefit Analysis of Upper Itchen Flow Augmentation The disruptions to the operation of the River Alre scheme and the resulting irregular flow pattern make it difficult to realistically assess its potential ecological impact if, and when, operated at full output. Therefore the majority of this section will focus on the Candover Stream scheme, with inferences made to the River Alre scheme where appropriate.
A key proponent for the operation of the Upper Itchen flow augmentation schemes were the ecological benefits they would provide during periods of low flow. However, it is considered that the most significant ecological benefits achieved from their operation would be associated with the alleviation of low flow conditions further downstream in the catchment; in particular the retention of unobstructed fish passage, prevention of strandings, and maintenance of suitable spawning habitats (Environment Agency, personal communication).
The original study investigating the potential effects of the Candover Stream Pilot scheme (Southern Water Authority, 1979) found little variation in aquatic plant biomass and invertebrate communities on the Candover Stream, and concluded that it is unlikely that the influence of the operation of the scheme would impose itself over natural variation. Furthermore, this study highlighted the benefits of the scheme to the
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tributaries of the Upper Itchen, alleviating the potential loss and modification of habitats associated with reductions in water levels and consequential shift in invertebrate communities to those that prefer low flow and silty conditions. In fact, the report suggests that medium to high summer flows would increase the range of habitats and would therefore support a greater number of species. The findings of the current study support this earlier work to a degree, with no evidence returned for an increase in macroinvertebrate drift and an increased diversity recorded (based on single samples) at Abbotstone Causeway following the operation of the Candover Stream Scheme. However, it is important to emphasise that flow conditions during this survey are considered to exceed summer high flows (see section 5.2.3), and as outlined below a number of potential adverse implications may therefore be associated with these uncharacteristic summer flow conditions.
The ecological monitoring undertaken during this study did not identify any direct adverse impacts on white-clawed crayfish from the operation of either the Candover Stream or River Alre schemes, and neither the expected increase in (juvenile) crayfish drift rates (Hutchings, 2004) nor any instances of drift associated mortality was recorded. However, it is considered that the potential implications associated with the operation of the Candover Stream scheme are more complex than discussed within the Pilot scheme report. Chalk headwater streams such as the Candover Stream support a diverse assemblage of species, some of which have only been recorded within the upper reaches (Mainstone, 1999), and these two upper tributaries of the River Itchen support the only remaining viable population of white-clawed crayfish in Hampshire. It is considered highly likely that a negative impact on white-clawed crayfish and more specialised headwater fauna will be associated with this scale of operation of the scheme. This level of flow augmentation generates uncharacteristic summer flow conditions (potentially prolonged and comparable to winter flows) within an otherwise stable hydrological regime to which the white-clawed crayfish are adapted (Hutchings, 2004). The key physico-chemical modifications associated with the operation of the Candover Stream flow augmentation scheme, and their associated effects (costs) on the resident white-clawed crayfish sub-population, are outlined in Table 7.1 and discussed in more detail below.
The operation of the Candover Stream scheme resulted in a substantial, visible increase in water depth and flow, with the latter demonstrating an almost two-thirds increase in four days and over a 80% increase over a ten day period. It is considered highly plausible that unrecorded increases in the levels of drift may have occurred, particularly in association with the rapid increase of flow during the early stages of the operation of the Candover Stream scheme or during the night when crayfish are conventionally more active. Even if not associated with direct damage or mortality, any such drift could result in the translocation of crayfish to areas of sub-optimal habitat, where they may be more susceptible to predation as a consequence of reduced foraging and sheltering resources. This is of particular concern downstream of the Upper Fobdown survey site, where the greatest concentrations of white-clawed crayfish reside. Long sections of the Candover Stream between the two Fobdown survey sites are dominated by a uniform substrate of coarse gravels and finer sediment, providing limited habitat heterogeneity and therefore refugia, leaving individuals at a greater risk to predation and susceptibility to further drift during high flow periods. Increased levels of drift could also result in an increased rate of transmission of disease. This could be through the transfer of porcelain-infected moribund individuals to downstream reaches with a lower prevalence of this disease, or in the worst case accelerate the downstream transfer of A. astaci (crayfish plague) spores, increasing the likelihood of the complete loss of the population before any response measures could be implemented. The preparation of a response plan to such an event is currently being undertaken (Rushbrook, in prep).
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In addition to the risk of unrecorded increased levels of drift, it is considered highly likely that these elevated summer flow rates will impose significant energetic costs on white-clawed crayfish to maintain their position within the channel, which would be at the expense of investment in growth and reproduction (i.e. development of gametes). This would exacerbate the observed reduction in maximum daytime water temperature within the marginal area, important in stimulating juvenile moulting and therefore growth. Combined, this could significantly impact both on the short-term survival of individual crayfish (i.e. increased risk of predation) and long-term recruitment to the Fobdown site.
The long-term effects of operating these two schemes on groundwater levels did not form part of this study, but potentially represents a highly significant adverse implication of these schemes. Previous testing and modelling has demonstrated that the longer term impact of the scheme is to reduce flow rates the following winter, influencing summer flow rates to a notably lesser degree (Environment Agency, personal communication). However, it is considered that the impact of the scheme on winter levels and its capacity (and severity) to continue into the summer months will be dependent on the degree to which groundwater levels were already suppressed (prior to operation) and the provision of sufficient winter re-charge of the aquifer. Since the schemes are designed to alleviate low water flows and increase water levels to, in part, meet abstraction demands, it is inherently likely to be drawing from an already depleted groundwater supply. Therefore, without sufficient winter re-charge of the aquifer, it is considered highly likely that the impacts associated with groundwater drawdown over a long period could have an adverse affect on the crayfish population through habitat modification, with the inherent risk of increased levels of predation and competition for space. This is a particular concern for those sections supporting the highest densities of crayfish, such as Upper Fobdown, and is emphasised by the significantly below average rainfall recorded during the winter preceding the 2011 test operation of the schemes; the second consecutive winter with below average rainfall.
Finally, it is recognised that the sympathetic operation of the Upper Itchen flow augmentation schemes would be beneficial during prolonged extreme low flow conditions (Hutchings, 2004). In this context, extreme low flow conditions are considered to represent a substantial reduction in the wetted width or depth (for example reduced to a third of the typical width / depth) of the headwater channel. In this instance the adverse implications associated with the operation of these schemes would be inherently reduced, and be significantly outweighed by the considerable negative impact that a major or complete loss of water and / or flow would have on the aquatic fauna; both those inhabiting these headwaters (including fish, white-clawed crayfish and other macroinvertebrates), as well as the important in-channel (i.e. the Ranunculion fluitantis and Callitricho-Batrachion vegetation community) and floodplain (i.e. south damselfly Coenagrion mercuriale) interest features of the River Itchen SSSI / SAC further downstream. However, the operation of these schemes, specifically on the Candover Stream, would require significant modification before it would be considered to be appropriate or sympathetic.
7.3. Future Operation of the Candover Stream Scheme It is recommended that the findings of this study be used to refine the operating procedures for the Candover Stream flow augmentation scheme. These operating procedures will be designed both to specifically minimise the potential impacts of the scheme on the highly important yet vulnerable resident white-clawed crayfish sub- population, and to meet the Environment Agency’s over arching requirement to modify all abstraction licences by 2015 to ensure they have no adverse effect on integrity of the River Itchen SAC (Environment Agency, personal communication).
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-
- reduction - reduction - reduction - reduction - reduction
ntial - increased increased -
- smaller individuals individuals smaller -
- individuals killed by in refugia reduction - - result of infection or in refugia reduction - or acute of result - r Stream flow augmentation scheme and pote scheme and flow augmentation r Stream in the energy available for individuals to invest in growth or reproduction reproduction or growth in invest to individuals for available energy in the reproduction or growth in invest to individuals for available energy in the reproduction or growth in invest to individuals for available energy in the reproduction or growth in invest to individuals for available energy in the invest to individuals for available energy therefore and opportunities foraging in reproduction or in growth reduced competitive ability of individuals / investment in limb regeneration regeneration limb in investment / individuals of ability competitive reduced in growth invest to individuals for available energy the in a reduction in resulting reproduction or age at sexual maturity maturity sexual at age collisions / impacts during drifting predation of risk an increased in resulting resources acute or chronic exposure to pollutants suitable from individuals some of exclusion in competitive resulting resourced refugia with an associated increased risk of predation of a result as potential or / pollutants conditions extreme to exposure chronic increased predation resulting from behavioural change associated the with individuals the of status stress increased Potential direct effects on the white-clawed crayfish sub- population population of individuals from the loss Direct subject to increased levels of predation due to increased susceptibility to gape gape to susceptibility increased to due predation of levels increased to subject / prey-size limited predators Direct loss of individuals from the population of individuals from the loss Direct year(s) in subsequent to population recruitment Reduced year(s) in subsequent to population recruitment Reduced year(s) in subsequent to population recruitment Reduced population of individuals from the loss Direct Direct loss of individuals from the population of individuals from the loss Direct population of individuals from the loss Direct Reduction in recruitment to population in subsequent year(s) in subsequent to population in recruitment Reduction population of individuals from the loss Direct year(s) in subsequent to population recruitment Reduced years in subsequent to population recruitment Reduced year(s) in subsequent to population recruitment Reduced tes (particularly juveniles)tes (particularly as activity resulting in decreased activity sociated with the operation of the Candove with the operation sociated Potential direct effects on individual white-clawed crayfish Increased rates of (unrecorded) daytime or over-night crayfish drift resulting in the death or of individuals injury Increased rates of (unrecorded) daytime or over-night crayfish drift resulting in displacement to areas of poor or sub-optimal habitat Retardation of individuals growth ra a result of reduced metabolic rates and associated fewer moults during summer / autumn and associatedReduction / quality in habitat availability increase in habitat fragmentation resulting in increased levels of intra- and inter-specific competition for resources Increase in speed of transmission or transfer of pathogens (i.e. crayfish plague) and / or pollutants resulting in the death of individuals Increased energetic cost to crayfish in maintaining position within the channel (i.e. resisting drift) Increased energetic cost in moving the water current within and association reduction of foraging intake efficiency (i.e. energy / expenditure) energy Behavioural reduction in foraging uptakeenergy Increase in water temperature, levelsreduction and in oxygen increase in concentrations of pollutants resulting in the death of individuals clawed crayfish sub-population. sub-population. crayfish clawed Summary of the physico-chemical changes as changes of the physico-chemical Summary Physico-chemical changes associated with the flow of the scheme operation augmentation Increase in rate flow (levels uncharacteristic of flows) summer typical Reduction in maximum daytime temperature water Reduced subsequent winter / spring / summer flow rates levels* and water * A consequence of (multiple) operation(s) of the flow augmentation scheme with inadequate winter aquifer re-charge Table 7.1: resulting effects on the resident white- resident on the resulting effects
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7.3.1. Operational Procedures and Output The likelihood and degree to which the operation of the Candover Stream scheme has the potential to adversely impact white-clawed crayfish will be determined by the timing, operating procedures (including output patterns and levels), and duration of its operation. Data and information gained from the test carried out in 2011 can be used to inform discussions about future operational procedures and consideration of the output of the schemes. Section 7.3.3 recommends how the concerns raised below could be addressed.
Although there was no evidence of a direct ecological impact during testing of the Candover Stream scheme in 2011, it is considered that the output procedures employed were not sufficiently precautionary. Specifically, it is considered that the increments in abstraction / discharge and associated flow rates during the early stages of the operation were considerably too great in volume and too frequent in occurrence. Data collected by Atkins Limited (and provided to the authors by the Environment Agency) recorded abstraction rates of 25Ml/d within three days of commencing (from zero) the operation of the Candover Stream scheme (Figure 7.1), with an associated 66% increase in flow rates within four days (Figure 4.2a). It is very strongly recommended that during any future operation the ‘ramping-up’ of the Candover Stream scheme be undertaken considerably more slowly, with small, regulated increases in flow rates introduced, simulating the typically staggered response of these chalk stream headwaters to rainfall / aquifer re-charge.
Furthermore, unseasonably high flow rates were associated with the operation of the Candover Stream scheme when compared with flow rate data for the September to October period over the past twelve years. As outlined above, it is considered highly plausible that this could have unrecorded direct and indirect adverse impacts on white-clawed crayfish, both at Fobdown Farm and throughout their distribution on this chalk stream. Though it is recognised that the test undertaken in 2011 was not carried out under the low flow conditions required to trigger a future operation of this scheme, it is recommended that a review of the maximum flow rates should be undertaken. This should ensure that the conclusions regarding the impact of the schemes on the flow regime made in the Site Action Plan are still valid.
In conclusion, it is considered that although the Site Action Plan addressed many issues of concern, new data collected shows that a more considered approach to the operation of the flow augmentation schemes are required, in particular for the Candover Stream scheme. In essence, the operation of the River Alre and Candover Stream schemes must be carefully planned and operated, and it is not considered appropriate to utilise these schemes as a rapid response measure to short term deficits in water supply or in reaction to periods of high demand.
7.3.2. Implications Associated with Anomalous Crayfish Behaviour The expression of this anomalous diurnal behaviour within a proportion of white- clawed crayfish at Upper Fobdown is a significant consideration for the future operation of the Candover Stream, and potentially the River Alre, flow augmentation scheme(s). It is considered that the expression of this anomalous behaviour has the potential to increase the susceptibility of this vulnerable crayfish population to the increased flow rates associated with the operation of these schemes. However, it is important to recognise that there was no evidence for a direct effect of the operation of the flow augmentation schemes, or the expression of anomalous behaviour, on levels of white-clawed crayfish drift or survival. Furthermore, without determining the cause of this anomalous behaviour, it remains difficult to accurately assess how it may
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interact with the potential effects of flow augmentation discussed above (i.e. undetected drift, indirect energetic costs, decreased maximum water temperatures).
80
70
60
50
40
30 Abstraction (Ml/d) Abstraction
20
10
0 03 Oct 03 Oct 2011 10 Oct 2011 17 Oct 2011 24 Oct 2011 31 Oct 2011 02 Jan 2012 09 Jan 2012 07 Nov 2011 14 Nov 2011 21 Nov 2011 28 Nov 2011 12 Sep 2011 Sep 12 2011 Sep 19 2011 Sep 26 2011 Dec 05 2011 Dec 12 2011 Dec 19 2011 Dec 26
Date
Figure 7.1: Summary representing cumulative abstraction rates from each of the pumping stations associated with the Upper Itchen flow augmentation schemes. Pumping stations associated with the Candover Stream and River Alre schemes are shown as shades of red and blue respectively.
The imposed delay in the operation of the Upper Itchen flow augmentation schemes reflects the implication of this diurnal behaviour on the viability of the scheme. Whilst the cause and potential impacts of this anomalous behaviour remains undetermined, there remains a conflict between the risk of compounding any negative effects associated with this behaviour and the need to secure sufficient water supply downstream. On the Candover Stream, it has been suggested that a possible solution is the construction of a new pipeline to allow groundwater to be pumped directly to the lower reaches, therefore by-passing the majority of the crayfish sub-population. There are significant and substantial ecological considerations associated with such measures, which are not within the remit of this report to discuss. However, it is important to acknowledge that the diversion of groundwater directly to the downstream reaches of the Candover Stream could have significant impacts, resulting in a depletion of the flow rates and water levels upstream. Therefore, it is considered highly likely that such an operation of the Candover Stream scheme may exacerbate existing low flow conditions, which are inherently linked to its operation. An auxiliary flow through the existing pipeline may be required to ensure that there are no adverse impacts of the scheme on white-clawed crayfish further upstream.
7.3.3. Proposed Amendments to Review of Consents Safeguards (Candover) The changes to the augmentation scheme licences proposed in the River Itchen Site Action Plan were designed to ensure that use of the augmentation schemes could not compromise the integrity of the River Itchen SAC. In summary, the changes are to:
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Modify both licences so they can only be used during low flow periods to support the new target flow regime. (i.e. to maintain flows above 198 Ml/d at Allbrook & Highbridge and to maintain flows at Riverside Park above 194 Ml/d) Modify Candover Scheme licence to restrict daily abstraction to 20 Ml/d between 1st May and 31st August; Include conditions in both licences to refer to an operating agreement.
Although the test in 2011 was not carried out under the low flow conditions that the schemes would be operationally required, it has provided additional information which can be used to improve the informal operating procedures currently used. These procedures need to be formalised as part of the review of consents process.
The recommendations outlined below aim to provide guidance on the timing, duration, and procedures (including output patterns and levels) for the operation of the Upper Itchen flow augmentation schemes, and should facilitate further technical discussions to determine the exact prescriptions for their operation. It is therefore recommended that: A gradual build up and reduction in abstraction levels be undertaken at all times of the year for both schemes, with a greater number of smaller stepwise increments than observed during the operation of the schemes in 2011. For example, for the Candover Stream scheme it is recommended that maximum stepwise increments be around 5Ml/d with an interval of at least four days between increments, extended to an interval between increments of one week prior to August 31st; If such fine scale increments cannot be achieved within the existing system, it is considered to be essential that modifications are made to allow for a greater degree of control in the volume of abstraction / discharge from each of the pumping stations; A programme of ecological monitoring (including water quality analysis) be agreed upon that includes the period prior to, during, and after the operation of both schemes. This programme should be implemented with all future uses of these schemes; A schedule of actions be prepared and implemented prior to future use of the both schemes such as channel maintenance and weed cutting.
In addition to informing development of a formal operating procedure, testing of the scheme in 2011 has raised new concerns about the amount of daily abstraction authorised by the licence and the impact this has on the flow regime of the Candover Stream. Within the Site Action Plan, these concerns had been resolved by restricting use of the Candover Scheme to 20 Ml/d from May to August, and by restricting use of both schemes to periods of exceptionally low flow. To ensure that these measures are appropriate, a re-assessment of the impact of the scheme on river flows under realistic operating scenarios and on SSSI / SAC target features and headwater ecology should be completed before the final operating procedures and licence changes are agreed.
Outside of the period from May to August, the proposed Candover Scheme licence has a daily limit of 36 Ml/d. Based on in-situ observations of the effects of the scheme's operation at Fobdown Farm, it is recommended that this limit be reduced to reflect the Autumn 2011 test’s intended maximum abstraction level, 26-27 Ml/d, representing approximately two-thirds of its existing abstraction capacity.
Finally, it is recommended that no increases in the outputs of the scheme should be undertaken beyond 15th October, and, if there has been sufficient late-summer / early
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autumn rainfall to maintain water levels typical for that time of year, a phased turning off of the flow augmentations schemes should be implemented from this date. This date reflects the approximate onset of the breeding period of white-clawed crayfish and the associated increased sensitivity / reduced mobility of the berried ‘egg-bearing’ females.
7.4. Recommendations
7.4.1. Mitigation and Enhancement As outlined above, it is considered highly plausible that there may exist undetected negative impacts of operating the Upper Itchen flow augmentation schemes on white- clawed crayfish. Hutchings (2004) identified the need to mitigate the potential risks of increased crayfish drift through habitat enhancement downstream of the crayfish population. Since the mid 2000’s, the Environment Agency has led on the implementation of a series of combined salmonid and crayfish enhancement projects (Holmes, 2007) on the Candover Stream above, within, and below Fobdown Farm. This has included the introduction of large flints, sedges and encouragement of localised overhanging bankside cover to provide refuge for juvenile trout and white- clawed crayfish. However, large sections of the Candover Stream remain dominated by homogenous, well sorted gravels and small stones. Specifically, a significant proportion of the Candover Stream between the two Fobdown survey sites, and the section immediately downstream of Lower Fobdown, are dominated by well sorted low grade substrate with limited available refugia features.
Increasing the heterogeneity of substrate and the inclusion of a range of complex habitat features will help mitigate the potential adverse impacts of drift on white- clawed crayfish, both through a reduction in the risk of drift (see sections 5.3.2. and 6.6.2) and increasing the likelihood that any drifting crayfish are displaced to areas of equal or greater habitat suitability. The inclusion of range of in-channel and marginal features will provide suitable refuge from high flows for all age cohorts of white-clawed crayfish. Furthermore, although it was not possible to discern the cause of the anomalous crayfish behaviour, if an increase in population density is in fact the driver for this, the provision of a greater availability of refugia would mitigate against this and any other negative consequences associated with a current or future population expansion.
The protection of existing / creation of new marginal gravel and flint berms should allow for the retention of areas of shallower water as levels rise and fall. This will both provide habitat for juvenile crayfish and potentially aid juvenile growth and development by maintaining areas that will positively respond to increases in solar radiation. The exact extent, nature and location of such work on both the Candover Stream and the River Alre will need to be determined in discussions with the appropriate river / floodplain owners and managers, but will be based on pre-existing recommendations outlined within a series of reports (Holmes, 2007; Rushbrook, 2011b, 2011c). Furthermore, where feasible these habitat enhancement works should be complemented by modification and improvements in management practices to allow a greater degree of connectivity between the channels and their floodplain. This will allow the channel to respond to the natural variations in water levels and demonstrate a greater robustness to the expected future trend of lower summer flows (Rushbrook, 2011b).
As conducted during this test period, it is recommended that landowner engagement and communication form part of the strategic operation of these schemes, and a two
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way dialogue be retained during the entire augmentation period. Key areas of discussion will include the timing and scale of weed management and management of off-take and outlet structures immediately prior to, and during the operation of these schemes. Furthermore, it is recommended that detailed ecological (crayfish) monitoring is employed during any future use of the Upper Itchen flow augmentation schemes, and a condition be imposed on its operation to allow for its suspension if any adverse impacts on white-clawed crayfish are recorded.
7.4.2. Future Work It is the intention of the authors to continue to monitor the presence / prevalence of the expression of the anomalous behaviour within the resident Candover Stream crayfish sub-population, and continue to endeavour to determine its cause through more detailed investigations into the potential ecological (abiotic and biotic) and anthropological causes of this behaviour.
Finally, it is recommended that annual spring / autumn macroinvertebrate surveying at Abbotstone be continued over multiple years. It is understood that, within chalk water systems, the effects of low flow rates are more likely to impact the invertebrate community during the following (or subsequent) spring(s), rather than immediately after or in association with a low flow event. This could be a consequence of lowered groundwater levels not receiving sufficient winter re-charge, and it is therefore a potential mechanism of measuring any longer term implications of aquifer drawn down associated with the (multiple) use of the Upper Itchen flow augmentation schemes.
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Appendix 1: Executive Summary of ‘A review of the potential impacts of the Candover Stream Augmentation Scheme on the native crayfish population at Fobdown Farm near Alresford, Hampshire.
This report discusses the potential impact of flow augmentation on the native crayfish Austropotamobius pallipes population in the Candover Stream, near Alresford Hampshire. The report aims to assist a review of the consents process for the River Itchen candidate Special Area of Conservation (cSAC) being undertaken by the Environment Agency in Autumn 2004.
Native crayfish in the Candover Stream have adapted to a stable flow regime characteristic of southern chalkstreams and their annual life cycle is finely tuned to the gross, macro and micro variations in channel flow velocity. The distribution of aquatic invertebrates generally is determined by a range of factors including flow velocity and many studies have looked at this relationship in some detail. Few specific studies have been undertaken on crayfish and their relationship with variations in channel flow, but there have been several investigations into the ecological and specific habitat preferences of the native British crayfish. These studies have revealed the requirements for a range of inter-related factors including a diverse physical habitat comprising an abundance of refuges, and moderate to slow flowing water. These requirements vary in accordance with the stage in the life cycle of an individual but are most critical during the early juvenile growing phase. Few studies have looked at the impact of extreme low flows on crayfish but the basic physiological requirements of the native crayfish are known and there is little doubt that such conditions would have a detrimental affect on this species.
The potential impact of flow augmentation on the crayfish population is discussed in relation to several possible scenarios:
A short one-off event, Continuous augmented flow in summer and The longer term implications of groundwater drawdown as a result of prolonged abstraction.
In summary the possible impacts of implementing the augmentation scheme as a short, one-off event are: Rapid increases in current velocity may lead to the loss of marginal habitat and refuges and increase the affects of drift on juveniles, An influx of lower temperature water will lead to cooling of marginal slack waters and shorten the growing period of juveniles, Some displacement and drift of individual crayfish, particularly juveniles, into unsuitable habitat areas downstream and within the Fobdown Farm stretch will occur, It is unlikely that colonisation downstream will happen, but the potential to establish a new colony will increase with the implementation of habitat enhancement work, Channel management practices could significantly increase the potential impact of augmentation, Late summer/early autumn augmentation may have lesser impact on the crayfish population than early and mid summer high flows.
In summary the possible impacts of implementing the augmentation scheme on a longer term basis over several months of the summer are:
Increased intensity of all the possible impacts mentioned earlier, The most serious implications relate to juvenile growth and survival, A small and regulated increase in flow velocity, simulating natural summer flows, could be beneficial but only at times of prolonged extreme drought.
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In summary the possible impacts of groundwater drawdown over a long period on the crayfish population at Fobdown Farm are:
Low flows in autumn/winter and the following spring/early summer could result in increased adult and juvenile mortalities as traditional refuges are lost, increasing interaction between age classes and exposure to predation, Low flows will lead to changes in habitat conditions, slower current velocity, increasing siltation, reduced marginal zone, infilling of refuges by silt will result in increasing fragmentation of the population, Elevated nutrient and depressed dissolved oxygen levels could lead directly to crayfish mortalities Implementing the augmentation scheme for short periods at times of extreme drought could benefit crayfish by at least ensuring their survival.
It is difficult to assess specific impacts but generally the following conclusions can be made:
No studies have assessed the direct impacts on a crayfish population of flow augmentation, but information on the ecological requirements and behaviour of this species can assist in investigating the potential consequences of such activities, Some form of negative impact will be inevitable, since augmentation represents an alien event (sometimes prolonged) in an otherwise stable hydrological regime, to which the native crayfish is adapted, Sympathetic use of the scheme at times of prolonged extreme drought conditions could be beneficial to the survival of the crayfish population, The level and intensity of impact will be determined by the timing and duration of flow augmentation and abstraction episode and the extent of a diverse in-stream habitat.
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Appendix 2: Original scheduled testing of the Candover Stream and River Alre flow augmentation schemes as outlined in Rushbrook (2011).
Candover Stream The augmentation flow for the Candover Stream scheme is provided from three pumping stations each of which comprises two boreholes with the potential to supply up to 6 megalitres per day (Ml/d) each. The scheme therefore has a maximum operating capacity of 36Ml/d, though a series of constraints on the intensities and timings have been imposed by the Environment Agency.
It is understood that the Candover Stream scheme will be operated at three different intensities: Short test – each of the boreholes will be individually tested for a period of approximately 12 hours. This will result in no more than 6Ml/d entering the Candover Stream per day for six separate days. Intermediate test – both boreholes will be pumped at each of the three pumping stations individually for a period of 1-2 days. This will result in no more than 10Ml/d entering the Candover Stream for 1-2 days on three separate occasions. Full output – scheduled to start in mid to late August, the augmented flows will be increased in 10Ml/d increments with the scheme restricted to 20Ml/d until the 1st September and maximum output probably occurring in mid / late September. Augmented flows will then be reduced incrementally with the scheme ‘turned off’ by early / mid October. A proposed plan for full output testing of the Candover Stream flow augmentation is provided in Table App 2.1.
Table App 2.1: Proposed plans for full output testing of the Candover Stream and River Alre flow augmentation schemes Candover Stream River Alre Timings Operating Level Operational Approx Operational Approx Stations output Stations output Week 0 Turn scheme on 1 10 Ml/d 1 12 Ml/d Week 1 Increase augmentation 2 20 Ml/d 2 25 Ml/d Week 2 Ramp to full opertation 3 30 Ml/d 4 50 Ml/d Week 3 Full operation 3 30 Ml/d 4 50 Ml/d Week 4 Full operation 3 30 Ml/d 4 50 Ml/d Week 5 Full operation 3 30 Ml/d 4 50 Ml/d Week 6 Decrease augmentation 2 20 Ml/d 2 25 Ml/d Week 7 Turn scheme off 1 10 Ml/d 1 12 Ml/d
River Alre The augmentation flow for the River Alre scheme is provided from a single borehole at four separate pumping stations, each with the potential to supply up to 14Ml/d. The scheme therefore has a maximum operating capacity of 56Ml/d.
It is understood that the River Alre scheme will be operated at two different intensities: Short test – each of the boreholes / pumping stations will be individually tested for a period of approximately 24 hours. This will result in no more than 14Ml/d entering the River Alre per day for four separate days.
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Full output – scheduled to start in August, the augmented flows will be increased incrementally with maximum output probably occurring in mid / late September. Augmented flows will then be reduced incrementally with the scheme ‘turned off’ by early / mid October. A proposed plan for full output testing of the River Alre flow augmentation is provided in Table App 2.1.
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Appendix 3: Threshold levels for the termination of the Upper Itchen flow augmentation schemes determined for both drift net monitoring and specific anomalous crayfish behaviour monitoring.
Summary
The following values have been calculated as the threshold values for each of the three crayfish monitoring sites, both in terms of rates of crayfish drift and the prevalence of crayfish presenting anomalous behaviour. In all cases, the values calculated exceed what is considered to be acceptable levels, and have been collectively agreed upon. Therefore, if these values are reached, it is strongly recommended that the appropriate scheme(s) are terminated immediately – though the operation of a single pump for each scheme may be necessary to allow fish time to retreat downstream with the reducing water levels.
Table App 3.1 provides a summary of these threshold levels and is followed by an explanation of their calculation. The methodologies for these two monitoring programmes have been provided in sections 5 and 6 of this report.
Table App 3.1:
Drift Net Prevalence of anomalous Scheme Monitoring Site (individuals) behaviour (%)
Candover Upper Fobdown Farm 849%
Candover Lower Fobdown Farm 320%
Alre D/s Drove Lane 320%
Crayfish Behaviour Monitoring
Upper Fobdown Baseline Survey 1 = 19 of 51 individuals collected from exposed areas (crayfish) = 37.25%
Baseline Survey 2 = 23 of 52 individuals collected from exposed areas (crayfish) = 44.23%
Baseline Means = 42 of 103 individuals collected from exposed areas (crayfish) = 40.78%
As outlined in our ‘Protocol for additional monitoring for crayfish abnormal behaviour’ (dated 14/09/11): we have determined up to 20% to be an acceptable degree of change over and above the extant baseline. Exceedence of this threshold suggests a significant worsening condition of an already stressed sub-population.
Threshold percentage for Upper Fobdown = 49%
Lower Fobdown Baseline Survey 1 = 0 of 22 individuals collected from exposed areas (crayfish) = 0.00%
Baseline Survey 2 = 0 of 18 individuals collected from exposed areas (crayfish) = 0.00%
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Baseline Mean = 0 of 40 individuals collected from exposed areas (crayfish) = 0.00%
However, a threshold value of 0% is considered unsatisfactory as it does not provide any flexibility (i.e. for individuals disturbed during the survey or moving between refugia) and can therefore not be considered a sensible value to infer a potential impact of the Candover Stream scheme. Furthermore, the relative low abundances recorded (in comparison with the Upper Fobdown monitoring site) mean that using a low percentage (i.e. 10%) would be of little greater value. Therefore, a value of 20% from a minimum sample size of ten individuals has been determined to provide a robust and pragmatic threshold level. Exceedence of this threshold provides significant indication of a previously undetected level of stress at this monitoring site.
Threshold percentage for Lower Fobdown = 20%
Downstream of Drove Lane Baseline† Survey 1 = 0 of 6 individuals collected from exposed areas (crayfish) = 0.00%
Baseline† Survey 2 = 1 of 16 individuals collected from exposed areas (crayfish) = 6.25%
Baseline† Means = 1 of 22 individuals collected from exposed areas (crayfish) = 4.54%
However, a threshold value of 5.45 (i.e. 4.54+20%) is considered unsatisfactory as it does not provide sufficient flexibility (i.e. for individuals disturbed during the survey or moving between refugia) and can therefore not be considered a sensible value to infer a potential impact of the River Alre scheme. Furthermore, the relative low abundances recorded (in comparison with the Upper Fobdown monitoring site) mean that using a low percentage (i.e. 10%) would be of little greater value. Therefore, a value of 20% from a minimum sample size of ten individuals has been determined to provide a robust and pragmatic threshold level. Exceedence of this threshold provides significant indication of a previously undetected level of stress at this monitoring site.
Threshold percentage for Downstream of Drove Lane = 20%
† N.B. Since no anomalous behaviour was observed within the River Alre sub-population the flow augmentation scheme was commenced prior to any crayfish specific baseline surveys being undertaken; these surveys were in fact undertaken on the day that pump 1 and pump 2 were switched on respectively.
Crayfish Drift Net Monitoring
During baseline surveys, crayfish were only recorded in the drift nets deployed in the Upper Fobdown stretch of the Candover Stream, but not on all occasions and (when present) only at low numbers. Therefore, the abundance data collected during the crayfish behaviour monitoring was considered to be more valuable in determining a threshold level of drift for each survey location. A value of 15% of the mean survey values has been determined to provide a robust and pragmatic threshold level, with exceedence of this threshold providing an indication of an actual increased level of drift as a result of the augmented flows.
Upper Fobdown Autumn Baseline Survey (Drift) 05/09/11 = 3 Autumn Baseline Survey (Drift) 13/09/11 = 1 Autumn Baseline Survey (Drift) 15/09/11 = 0
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Threshold for number of individuals recorded in drift nets based on 15% of the mean number of crayfish collected in crayfish behaviour monitoring:
( ( 51 + 52 = ( × 0.15 2
= 7.7
Threshold no. individual crayfish in Upper Fobdown Drift Nets = 8
Lower Fobdown Autumn Baseline Survey (Drift) 05/09/11 = 0 Autumn Baseline Survey (Drift) 13/09/11 = 0 Autumn Baseline Survey (Drift) 15/09/11 = 0
Threshold for number of individuals recorded in drift nets based on 15% of the mean number of
crayfish collected in crayfish behaviour monitoring:
( ( 22 + 18 =× 0.15 ( 2
= 3.0
Threshold no. individual crayfish in Upper Fobdown Drift Nets = 3
Downstream of Drove Lane Autumn Baseline Survey (Drift) 05/09/11 = 0
Threshold for number of individuals recorded in drift nets based on 15% of the mean number of
crayfish collected in crayfish behaviour monitoring:
( ( 12 + 16 = ( × 0.15 2
= 2.1
Threshold no. individual crayfish in Upper Fobdown Drift Nets = 3
Tim Sykes (EA), Dr Ben Rushbrook (HIOWWT) and Dr Kerry Evans (EA) 20th September 2011*
* Document has been amended for this report but the underlying information agreed by the above parties has remained the same
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Appendix 4: Comparison of the flow rates at Borough Bridge during 2011 with the corresponding data for each year between 2000 – 2010 inclusive.
Flow (m3/s) 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 1Jn0-e 1Mr0-p 1My0-u 1Jl0-u 1Sp0-c 1Nv01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 1Jn0-e 1Mr0-p 1My0-u 1Jl0-u 1Sp0-c 1Nv01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 2000 2002 2011 2011 Date 0.00 0.50 1.00 1.50 2.00 2.50 3.00 0.00 0.50 0.50 1.00 1.00 1.50 1.50 2.00 2.00 2.50 2.50 1Jn0-e 1Mr0-p 1My0-u 1Jl0-u 1Sp0-c 1Nv01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 01-Dec 01-Dec 01-Nov 01-Nov 01-Oct 01-Oct 01-Sep 01-Sep 01-Aug 01-Aug 01-Jul 01-Jul 01-Jun 01-Jun 01-May 01-May 01-Apr 01-Apr 01-Mar 01-Mar 01-Feb 01-Feb 01-Jan 01-Jan 2003 2001 2011 2011
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Flow (m3/s) 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1Jn0-e 1Mr0-p 1My0-u 1Jl0-u 1Sp0-c 1Nv01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 2006 2004 2011 2011 Date 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 1Jn0-e 1Mr0-p 1My0-u 1Jl0-u 1Sp0-c 1Nv01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 2007 2005 2011 2011
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Flow (m3/s) 0.00 0.20 0.40 0.60 0.80 1.00 1.20 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1Jn0-e 1Mr0-p 1My0-u 1Jl0-u 1Sp0-c 1Nv01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 2008 2010 2011 2011 Date 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1Jn0-e 1Mr0-p 1My0-u 1Jl0-u 1Sp0-c 1Nv01-Dec 01-Nov 01-Oct 01-Sep 01-Aug 01-Jul 01-Jun 01-May 01-Apr 01-Mar 01-Feb 01-Jan 2009 2011
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Appendix 5: Range and average values of specific chemical values recorded during routine water quality (chemistry) monitoring at Abbotstone Causeway during 2010.
Abottstone 2010 Factor Range Mean
Ammonia (mg/l)* 0.03 0.03
Biological Oxygen Demand 1.0 - 1.5 1.1 (mg/l)*
Dissolved Oxygen (%) 81.5 - 125.4 94.5
Souble Reactive Phosphate 0.02 - 0.031 0.022 (mg/l)* pH 7.41 - 8.07 7.74
* A number of samples contained concentrations below the lowest level of detection for this variable
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Appendix 6: Graphical analysis of specific chemical variables and flow rates between 1st September and 7th November on the Candover Stream at Abbotstone Causeway and River Alre at The Soke. Solid triangles (▲) represent flow rates and open squares (□) represent associated chemical variables.
Comparison of flow rates and ammoniacal Nitrogen at Abbotstone Causeway
0.8 0.40
0.7 0.35
0.6 0.30
0.5 0.25 /s) 3 0.4 0.20 Flow (m 0.3 0.15 Ammoniacal Nitrogen (mg/l) Ammoniacal 0.2 0.10
0.1 0.05
0.0 0.00 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
Comparison of flow rates and ammoniacal Nitrogen at Drove Lane
1.8 0.4
1.6 0.35
1.4 0.3
1.2 0.25
/s) 1.0 3 0.2 0.8 Flow (m 0.15 0.6 Ammoniacal Nitrogen (mg/l) 0.1 0.4
0.2 0.05
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
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Comparison of flow rates and biological oxygen demand at Abbotstone Causeway
0.8 1.6
0.7 1.4
0.6 1.2
0.5 1 /s) 3 0.4 0.8 BOD (mg/l) BOD Flow (m Flow 0.3 0.6
0.2 0.4
0.1 0.2
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
Comparison of flow rates and biological oxygen demand at The Soke
1.8 1.6
1.6 1.4
1.4 1.2
1.2 1
/s) 1.0 3 0.8 0.8 BOD (mg/l) Flow (m Flow 0.6 0.6
0.4 0.4
0.2 0.2
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
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Comparison of flow rates and dissolved oxygen at Abbotstone Causeway
0.8 180
160 0.7
140 0.6
120 0.5
/s) 100 3 0.4
80 (%) DO Flow (m Flow 0.3 60
0.2 40
0.1 20
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
Comparison of flow rates and dissolved oxygen at The Soke
1.8 180
1.6 160
1.4 140
1.2 120
/s) 1.0 100 3
0.8 80 DO (%) Flow (m Flow
0.6 60
0.4 40
0.2 20
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
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Comparison of flow rates and soluble reactive (ortho-) phosphate at Abbotstone Causeway
0.8 0.2
0.18 0.7
0.16 0.6 0.14
0.5 0.12 /s) 3 0.4 0.1 Flow (m Flow 0.08 0.3 Orthophosphate (mg/l) Orthophosphate 0.06 0.2 0.04
0.1 0.02
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
Comparison of flow rates and soluble reactive (ortho-) phosphate at The Soke
1.8 0.2
1.6 0.18
0.16 1.4
0.14 1.2
0.12
/s) 1.0 3 0.1 0.8 Flow (m Flow 0.08
0.6 (mg/l) Orthophosphate 0.06
0.4 0.04
0.2 0.02
0.0 0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
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Comparison of flow rates and pH at Abbotstone Causeway
0.8 8.3
8.2 0.7
8.1 0.6 8
0.5 7.9 /s) 3 0.4 7.8 pH Flow (m Flow 7.7 0.3
7.6 0.2 7.5
0.1 7.4
0.0 7.3 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
Comparison of flow rates and pH at The Soke
1.8 8.3
1.6 8.2
8.1 1.4
8 1.2
7.9
/s) 1.0 3 7.8 pH 0.8 Flow (m Flow 7.7
0.6 7.6
0.4 7.5
0.2 7.4
0.0 7.3 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
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Comparison of flow rates and total phosphate at Abbotstone Causeway
0.8 0.30
0.7 0.25
0.6
0.20 0.5 /s) 3 0.4 0.15 Flow (m Flow
0.3 (mg/l) Phosphate 0.10
0.2
0.05 0.1
0.0 0.00 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
Comparison of flow rates and total phosphate at The Soke
1.8 0.30
1.6 0.25 1.4
1.2 0.20
/s) 1.0 3 0.15 0.8 Flow (m Flow Phosphate (mg/l) Phosphate 0.6 0.10
0.4 0.05 0.2
0.0 0.00 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
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Comparison of flow rates and suspended solids at Abbotstone Causeway
0.8 7.0
0.7 6.0
0.6 5.0
0.5 4.0 /s) 3 0.4
Flow (m Flow 3.0 0.3 Suspended Solids (mg/l) Solids Suspended 2.0 0.2
1.0 0.1
0.0 0.0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
Comparison of flow rates and suspended solids at The Soke
1.8 7.0
1.6 6.0
1.4
5.0 1.2
4.0 /s) 1 3
0.8 3.0 Flow (m Flow
0.6 Suspended Solids (mg/l) Suspended Solids 2.0
0.4
1.0 0.2
0 0.0 25/08/2011 04/09/2011 14/09/2011 24/09/2011 04/10/2011 14/10/2011 24/10/2011 03/11/2011 13/11/2011 Date
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Itchen Implementation NEP Scheme Appendix F. Section 32 Details
Atkins Pump testing and associated investigations of the Candover and Alre augmentation schemes, summer 2011 | Version 6.0 | November 2012 245
Consent H/2011/02/245 No:
CONSENT TO INVESTIGATE A GROUNDWATER SOURCE Section 32(3) Water Resources Act 1991
This CONSENT is issued by the Environment Agency ("the Agency") to:
Elliot Tinton, SSD Area Environmental Planning Team Leader, of Environment Agency, Guildbourne House, Chatsworth Road, Worthing, West Sussex, BN11 1LD ("the Consent Holder").
This consent authorises the Consent Holder to: abstract water for testing purposes from that well, borehole or other work at Alre Augmentation Scheme
National Grid Reference: West End Vale SU 63634 36027 Ropley Soke SU 65327 33973 Gilbert Street SU 65382 32613 Soames Farm SU 65271 30809 subject to the conditions set out in the Schedules 1 and 2 to this consent.
This consent is effective from the date below and expires on 1st August 2012
Signature Print name
Suzanne Fewings
Position Date GWHCL Team Leader, Solent & South Downs
This consent is issued by the Environment Agency, South East Region from its office at Colvedene Court, Wessex Way, Colden Common, Hampshire, SO21 1WP. The person whom the Consent Holder should contact during the carrying out of the works and if he has any queries is Sarah Ritchie, Technical Office GWHCL, tel.ext/direct line 01962 764984.
1 Consent H/2011/02/245 No:
SCHEDULE 1 - General Conditions
1 INTERPRETATION pollution/physical disturbance applies to any such pumping operations. a) "The Consent Holder" means the person (whether an individual or 3 SURVEY organisation) to whom this consent The works shall not proceed unless and is granted. Where the Consent until the Agency has informed the Holder is two or more persons (e.g. Consent Holder in writing to the effect a partnership) such persons shall that (i) it considers the survey of water be jointly and severally liable for the sources and other features which may proper fulfilment of the conditions of be relevant to the works as specified by this consent. In this consent the the Agency has been carried out expression may also include, where adequately and (ii) it appears unlikely the context so admits, a person that test pumping will significantly affect who is the applicant for a consent other water users. i.e. before a consent is granted. b) "The works" means the activities 4 NOTICES etc TO THE authorised or required by this AGENCY consent, including the survey, construction of the well, borehole, Unless other periods are agreed in well points, catchpit, or other work, writing with the Agency, the Consent and/or test pumping of the same, Holder shall give written notice to the as the context so requires. The Agency as follows:- expression "the works" does not include activities for which this a) 5 days' notice before first consent is unnecessary, such as commencing construction of the construction of ancillary buildings, works access roads, pits for drill cuttings, etc. b) 5 days' notice before commencing acidisation or other treatment of the 2 CLEARANCE/DEVELOPMENT works PUMPING c) 10 days' notice before commencing Clearance/development pumping to test pumping. remove any products of the well drilling or well development treatment is Notice, and other information required permitted under this Consent for a by the Agency, shall be sent to the period not exceeding 48 hours. office at the address shown on the front Clearance/development pumping that of this consent for the attention of the extends beyond 48 hours must be person named there. agreed with the Agency prior to the commencement of pumping. There must be a full recovery of water levels 5 DISCHARGE OF WATER and before a proper test pumping POTENTIAL FOR POLLUTION/ commences. Condition 5 of Schedule 1 PHYSICAL DISTURBANCE of this Consent concerning the discharge of water and potential for
2
Consent H/2011/02/245 No:
a) The Consent Holder shall construct The Consent Holder shall immediately and finish the works so that water is inform the Agency if any information or prevented from running to waste. complaint is received by him about the Any artesian flow must be securely consented operation, and shall capped. immediately consult with the Agency as to the appropriate action to be taken. b) The Consent Holder shall secure any completed works so as to 7 RECORDS prevent pollution or other hazard through those works, for example The Consent Holder shall keep such by capping and locking a records of strata encountered, completed borehole. construction of the works, results of any geophysical logging, water quality c) The Consent Holder shall ensure analyses, and test pumping data as that pollution of, interference with, may be required by the Agency. The or damage to inland freshwaters or information shall be given on forms groundwater does not occur, provided by the Agency, and/or on whether from abstracted water or compatible computer disk in a format from substances or materials used agreed with the Agency. These records in connection with the works. must be returned within one month of completion of the works or with any d) The Consent Holder shall be subsequent licence application responsible for obtaining necessary (whichever is sooner). consents in relation to structures in, over or under watercourses. 8 PRESENTATION OF RESULTS
e) The Consent Holder shall be The Consent Holder shall present responsible for the proper disposal results and analysis of test pumping in of wastes from the works. the form specified in Schedule 2 to this consent. f) The Consent Holder shall notify neighbouring landowners who may 9 INFORMATION TO THE BRITISH be affected by discharge from the GEOLOGICAL SURVEY (BGS) works and, if applicable, the ON BEHALF OF THE NATURAL Internal Drainage Board for the ENVIRONMENT RESEARCH area, and shall take all necessary COUNCIL steps to prevent flooding. a) Where the proposed works are g) The Consent Holder shall ensure intended to be more than 15 metres that all persons engaged in the (50 feet) deep, the Consent Holder works are free from, and are not must notify BGS before starting the carriers of, waterborne diseases, works. BGS' address for the and shall ensure that they operate purpose is the Hydrogeology to a high standard of hygiene. Group, British Geological Survey, Maclean Building, Crowmarsh 6 EFFECTS ON OTHER WATER Gifford, Wallingford, Oxon OX10 SOURCES 8BB.
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b) The Consent Holder shall send safely observed. The datum level on the BGS stratigraphic and test pumping gauge board shall be accordingly information as required by section levelled to Ordnance Datum (Newlyn). 198 Water Resources Act 1991 within one month of completing the 12 ENTRY BY THE AGENCY or BGS work. By arrangement with BGS, the Agency will do this on behalf of The Consent Holder shall allow the Consent Holder unless the representatives of the Agency or BGS Consent Holder instructs otherwise. to enter the site at all reasonable hours, to inspect the works, to inspect and take c) Under “The Borehole Sites and copies or extracts of documents, and to Operations Regulations 1995” take measurements and samples, as HSE must be notified when drilling such representatives consider boreholes more than 30 metres appropriate. deep into used or disused mining areas. The regulations define 13 STANDARDS OF WORK “mining area” as land within one kilometre in a horizontal or other Unless otherwise specified in this direction of workings in a mine, or consent or subsequently agreed with where a licence to mine for the Agency, the Consent Holder shall minerals has been granted. carry out the works and present data fully in accordance with British Standard 10 DRILLING SAMPLES ISO 14686 (2003) "Hydrometric n/a determinations – pumping tests for water wells – considerations and guidelines for design, performance and 11 MEASUREMENT ACCESS use". Copies of this are available from BSI, 389 Chiswick High Road, London, The Consent Holder shall provide an W4 4AL. Tel: (020) 89969000. access tube of diameter adequate for http://www.bsi-global.com/. The measuring instruments to be lowered Agency may require repetition of tests safely into the borehole. In the case of or other appropriate remedial activities lagoons, the consent holder shall install should the required standards not be a gauge board, of a design approved by met. the Agency, in a position in the lagoon so that at all times the full range of water levels from normal top water level to the maximum drawdown level can be
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Consent H/2011/02/245 No:
SCHEDULE 2 - Special Conditions
1. BACKGROUND
The Environment Agency Area Environment Planning Team are working with Southern Water and Portsmouth Water companies to decide the best way to manage water resources in Southern Hampshire over the coming years. Part of this work is to understand the role of the augmentation schemes and to see if they are still able to support the river during dry periods when demand for water is higher. We have not carried out any significant testing of the Environment Agency owned augmentation schemes since 1989/90. We now need to test both the Alre and Candover Schemes over the summer period to see how much water they can put into the River Itchen and to confirm our understanding of the impacts the schemes have on other licence holders and the environment. Flows in the River Itchen and its headwaters are low following a dry spring so it is a good time to test the schemes. Our recent groundwater modelling work has shown that use of the schemes is unlikely to have a significant effect on river flows and groundwater levels over the winter of 2011 or into the summer of 2012.
We expect to run the augmentation schemes for a period of several weeks in July, August and September 2011. The impact of this will be to keep flows in the Candover Stream, River Alre and River Itchen slightly higher than would be expected for this year. Working with Southern Water, we will be monitoring groundwater levels and riverflows throughout the River Itchen and its tributaries. We are also working with Hampshire Wildlife Trust to monitor the impact of the schemes on sensitive species in the Candover Stream and River Alre.
We need the S32 consent as the test will be operating outside of licensed conditions; the river level at the start of the test will not be below 240Ml/d Allbrook and Highbridge gauging station.
2. PROGRAMME.
The Consent Holder shall carry out test pumping and measurement of water levels in the works and at other points using a constant rate test. Full details of your test requirements are given in Appendix 1.
You must ensure that the turning on and off of the boreholes is phased so that there is adequate water/recovery of groundwater & river levels for the environment and licence holders.
During the test[s] pumping rates shall not exceed a maximum of 2333 m3/hr, 56000 m3/d.
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3. WATER LEVEL MONITORING
The Consent Holder is required to monitor the following specified water and wetland features.
3a. At the pumped source The Consent Holder shall measure water levels as shown on the attached data sheets from the commencement and completion of each pumping session until full recovery. Discharge rates or meter readings must be recorded at the minimum frequency during pumping. Any transducers installed must be capable of resolving fluctuations in pressure equivalent to 0.02 metres of water or less. Data should be recorded at 15 minute intervals or less using a data logger.
3b. Water Feature Monitoring Points Measurements will be required at boreholes listed in Appendix 2. They will be monitored by Atkins on behalf on Southern Water. Any transducers installed must be capable of resolving fluctuations in pressure equivalent to 0.02 metres of water or less. Data should be recorded at 15 minute intervals or less using a data logger.
We looked at our protected rights and abstraction licence databases. Those boreholes & wells that had been drilled after the test of 1989 were analysed in the ‘Water Features Survey’ to assess if they were at risk of being adversely impacted by the operation of the Alre Scheme. Appendices 3 and 4 show the list of boreholes that we felt needed further investigation; any actions taken are listed alongside those sites.
When the Alre Augmentation Scheme licence was issued, some agreements were drawn up with a number of licence holders (generally cressbed agreements) to resolve derogation concerns. We have reassessed the impact that this test will have on those licence holders. Information and any actions taken can be found in Appendix 4.
3c Streamflow Measurement The Consent Holder shall carry out streamflow measurements before, during and after test pumping: - at Bishops Sutton cressbeds and - at the standard Environment Agency gauging stations.
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4. WATER QUALITY
Samples shall be taken from each borehole before commencement of the test.
A protocol for the ecological monitoring of the Alre Augmentation scheme has been completed by Dr Ben Rushbrook., see Appendix 5.
DISCHARGE OF WATER
The Consent Holder shall discharge water through the pipes connected to the augmentation boreholes and into the River Itchen as detailed in licence number 11/42/22.2/169 (32/070).
5. PUMPING TEST RESULTS
The Consent Holder shall present results of test pumping in a form to be specified by the Environment Agency or in a format as otherwise be agreed in writing by the Agency before testing commences.
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