Study of Interaction Between Broad Oak Reservoir and Richborough Connection Project South East Water and National Grid

Study of interaction between Broad Oak Reservoir and Richborough Connection Project South East Water and National Grid

Stage 1a Study

B14000AG/BORStudy/801 Revision 2 28/04/2016

Document history and status

Revision Date Description By Review Approved

Ros Vincent & 0 18/06/2015 Draft John Gosden A J Smith Marcus Francis

Ros Vincent 1 28/08/15 Stage 1a Final John Gosden A J Smith Chris Fisher

Ros Vincent 2 28/04/16 Stage 1a Revised Final John Gosden A J Smith Chris Fisher

Distribution of copies

Revision Issue Date issued Issued to Comments

approved

South East Water & Issued as Draft for Comment 0 A J Smith 18th June 15 National Grid

28th August South East Water & 1 A J Smith Issued as Final Stage 1a Study Report 2015 National Grid

South East Water & Issued as Revised Final Stage 1a Study Report - Minor text 2 A J Smith 28th April 16 National Grid changes (typos and clarifications) and risk methodology revised.

Stage 1a Study

Study of interaction between Broad Oak Reservoir and Richborough Connection project Project no: B14000AG Document title: Stage 1a Study Document No.: B14000AG/BORStudy/801 Revision: 2 Date: 28th April 2016 Client name: South East Water and National Grid Client no: Project manager: Alaistair Smith Author: Ros Vincent / Chris Fisher File name: B14000AG-BORStudy-801_Study of Interaction between Broad Oak Reservoir and RCP_Rev 2_Final for Issue.docx

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B14000AG/BORStudy/801 – Rev 2 i Stage 1a Study

Contents Executive Summary ...... 1 1. Introduction ...... 3 1.1 Purpose of Report ...... 4 1.2 Scope of work ...... 4 2. Study Approach and Baseline Data ...... 6 2.1 Previous studies ...... 6 2.2 Topographic survey data ...... 7 2.3 Geo-environmental assessment ...... 7 2.4 Geomorphology and Water Framework Directive ...... 10 2.5 Aquatic Ecology ...... 12 2.6 Terrestrial ecology ...... 16 2.7 Landscape and visual ...... 17 2.8 Cultural Heritage ...... 19 2.9 Hydrology ...... 20 2.10 Flood study ...... 22 2.11 Water resources modelling ...... 23 3. Reservoir outline design ...... 27 3.1 Overall reservoir concept ...... 27 3.2 Sarre Penn Diversion Outline design ...... 28 3.3 Dam right abutment outline design ...... 35 3.4 Permanent Access ...... 40 3.5 Pipeline outline design ...... 41 4. Outline environmental mitigation and enhancement for the reservoir ...... 47 4.1 Stakeholder Requirements ...... 47 4.2 WFD Compliance ...... 48 4.3 Terrestrial ecological: Potential Impacts ...... 49 4.4 Aquatic Ecology: Potential Impacts ...... 50 4.5 Landscape and Visual: Potential Impacts ...... 50 4.6 Cultural Heritage: Potential Impacts ...... 53 4.7 Indicative Mitigation Requirements ...... 54 4.8 Summary of Key Impacts and Mitigation Requirements ...... 58 5. Reservoir with the Richborough Connection ...... 63 5.1 Introduction ...... 63 5.2 Engineering ...... 63 5.3 Environmental Mitigation ...... 65 6. Conclusions and Recommendations ...... 71 6.1 Introduction ...... 71 6.2 Key Findings ...... 71 6.3 Risks and Mitigation ...... 73

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Appendix A. Aquatic Ecology Walkover Report Appendix B. Extended Phase 1 Habitat Survey Report Appendix C. Hydrological Study Appendix D. Geomorphological Study Appendix E. Environmental Constraints Report – Cultural Heritage Appendix F. Geo-environmental Desk Study Appendix G. Drawings & Concept Plan Appendix H. Pipeline Data Sources Summary

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Executive Summary

National Grid (NG) is following a programme to submit a Development Consent Order (DCO) application for the Richborough Connection Project (RCP) in the autumn of 2015 and to this end published its proposed route (Route option C of the alternative options considered by NG to the north of Broad Oak) for formal pre- application consultation in February 2015. NG believes the preferred route provides the best balance between public and stakeholder interests and based on the information received to date that it is possible to integrate the RCP with the proposed reservoir. NG plan to construct the RCP in 2017/2018.

An initial study was undertaken by Jacobs in 2014, commissioned by South East Water (SEW) and funded by NG to define a concept plan for the reservoir including an indicative development footprint within the proposed RCP corridor area. This study was undertaken to understand potential issues and inform discussion on options. The study was based on a reservoir maximum 36.0m Above Ordinance Datum (AOD) top water level (TWL). The study highlighted uncertainty over the design of the Sarre Penn river diversion required to meet Water Framework Directive (WFD) requirements and also concerns raised over implications for the construction of the dam, potential restrictions to mitigation planting to provide woodland connectivity and for the supply pipeline as well as ecological and recreational amenity implications.

To address these concerns and uncertainty NG and SEW agreed that a further study be undertaken by Jacobs, co-funded by NG and SEW. The Terms of Reference for this study were proposed by Jacobs and agreed by SEW and NG. For this study, a phased approach has been agreed to allow the scope to be focused on the key issues as the work proceeds and also to align with NG’s DCO application preparation and post submission work.

The objective of the Stage 1 study was to develop the outline design for the reservoir, with particular focus upon the relationship and interaction with the RCP alignment and to use the output from this work to comment on and inform the development of the RCP and give assurance to both NG and SEW that both projects can co-exist now and in the future, ahead of the NG DCO application at the end of autumn 2015.

The draft study 1a findings have been subject to discussion with National Grid and South East Water and were presented at a meeting on 13th July 2015 to Natural England and Environment Agency and comments from all parties have been taken into account to determine the focus for additional study to be undertaken in stage 1b.

Key findings from the stage 1a study include:  Limitations on tree height within the pylon route corridor would limit provision of high canopy trees along the Sarre Penn riparian corridor and within the associated woodland planting belts. This limitation together with the regular vegetation maintenance required could reduce the effectiveness of the enhancement to woodland connectivity required for the reservoir scheme. There is potential to develop a coordinated planting and maintenance strategy for the RCP and reservoir scheme to reduce the effects of the limitation and maintenance, for example by applying approaches used by NG within woodland SSSIs.  The pylon between the reservoir top level and the Sarre Penn diversion (pylon PC9) and associated pylon access for future maintenance may restrict the future river diversion corridor design. Further studies are required to look at the river diversion design requirements in more detail involving additional river flow information, geomorphological study and engineering design. The Environment Agency has highlighted the need to demonstrate that the diversion channel can meet WFD requirements including providing functional habitat for brown trout.  Engineering structures at the south end of the dam abutment where the RCP route oversails a proposed access bridge over the river diversion; this bridge is part of the access to the dam crest and the cycleway and also links with the Sarre Penn corridor bridleway/access. This presents potential conflict between the RCP and the dam crest access and also potential additional visual and habitat continuity issues.  The fish pass design is likely to require more space than indicated on concept plans to date to provide the river gradient and pools and associated habitat to meet the species passage requirements within the head drop from the diversion channel. There is potential for interaction between the fish pass design, the RCP

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pylon south of the water treatment works (pylon PC10), water treatment works and reservoir mitigation planting requirements to provide screening from key cross valley views from the north. The fish pass design needs to be developed to allow the interactions to be considered further.  Key existing view-points are highlighted at Blaxland Farm and Calcott. Future new key view-points need to be considered with the reservoir from the visitors centre. These views could be affected by the RCP. Further work on landscape visualisation is required to quantify the impact from the interaction of the RCP on the reservoir.  The impacts from the secondary embankment and the 36m AOD reservoir are concerns that have been highlighted by Natural England and further study is required to assess shading effects, flooding from the catchment upstream of the secondary embankment and also to consider further the implications of the range of reservoir size on the diversion channel design.  The interaction between the RCP and the river diversion channel present significant risk to construction of the river diversion as the RCP would be in place in advance of the river diversion excavation works. A CDM review of the reservoir and river diversion construction should be undertaken by SEW and risks highlighted and communicated to the RCP Principal Designers to aid informing their design process to mitigate/or reduce those risks to the future construction of the reservoir scheme. The additional areas for study are proposed as part of the scope for the stage 1b study. This study scope will be agreed with SEW and NG and will also be made available to Environment Agency and Natural England for comment.

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1. Introduction

South East Water (SEW) included Broad Oak Reservoir in the adopted Water Resource Management Plans (WRMP) for 2010 and 2014 following extensive consultation and approval by Defra. Broad Oak Reservoir is an important strategic water resource for the region and is planned to be developed by 2033 on land purchased by SEW for this specific purpose. The reservoir will be constructed sometime after the RCP is in place. As the proposed RCP route corridor lies within the reservoir development footprint, SEW has concerns that the RCP will compromise the potential to deliver the reservoir scheme while meeting objectives and mitigation committed to in WRMP14 and also meeting the relevant regulatory requirements including the Water Framework Directive (WFD). Therefore, there is a need to progress the reservoir proposals much earlier than would otherwise be required to sufficiently engage with the RCP process.

An initial study was undertaken by Jacobs, commissioned by SEW and funded by NG to define a concept plan for the reservoir including an indicative development footprint within the proposed RCP corridor area. This study was undertaken to understand potential issues and inform discussion on options. The study was based on a maximum 36m Above Ordinance Datum (AOD) top water level (TWL). The study highlighted uncertainty over the design of the Sarre Penn river diversion required to meet WFD requirements, but also concerns over implications for the construction of the dam, potential restrictions to mitigation planting to provide woodland connectivity and for the supply pipeline as well as ecological and recreational amenity implications. Meetings took place with NG, SEW and Natural England (November 2014) and between SEW and the Environment Agency (January 2015).

This initial study on the concept plan for the reservoir has not altered NG’s preference for Route Option C (reference #appendix 2 of the Technical Appendix of the Preliminary Environmental Information Report (PEIR),link http://richboroughconnection.co.uk/assets/downloads/2.4%20PEIR%20Appendices%20(Technical).pdf), published for consultation in February 2015. Furthermore, the proposed limit of deviation and access routes for maintenance published as part of the NG pre-application consultation in February 2015, indicate potential additional areas of conflict or uncertainty which could affect both schemes and will need to be addressed.

The objective of the Stage 1 study is to develop the outline design for the reservoir, with particular focus upon the relationship and interaction with the RCP alignment and to use the output from this work to comment on and inform the development of the RCP and give assurance to both NG and SEW that both projects can co-exist now and in the future, ahead of the NG DCO application in autumn 2015.

Stage 2 would follow on at the end of Stage 1 with the scope to be agreed in discussion with Natural England and the Environment Agency. Stage 2 is intended to develop clarity on the interaction between the future reservoir outline design and the RCP DCO submission, including the river diversion, in parallel with the ongoing DCO planning process through the remaining part of 2015 and 2016.

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1.1 Purpose of Report

This report addresses the findings of the first part of the stage 1 study referred to as Stage 1a and aims to confirm the corridor required for all the reservoir components in the area of its interaction with the RCP and identification of potential conflicts.

This stage focuses on determining the corridor required to ensure that the deliverability and acceptability of both projects will not be compromised including engagement with Natural England and the Environment Agency to obtain their views. The study sets out:  initial proposals for the Sarre Penn river diversion to fulfil WFD, fish pass and engineering requirements  outline engineering requirements for the dam right abutment, permanent access and pipeline routing, in locations where they interface with the RCP  initial proposals for the mitigation planting strategy along the river corridor and the dam right abutment

The study covers the aspects which are relevant to the deliverability and acceptability of the design of the river diversion, dam, permanent access and pipeline structures with its associated environmental mitigation and enhancement where they interact with the RCP preferred route or revisions.

This report also makes recommendations for the scope of the next stage (1b) which will aim to reach an agreed Statement of Common Ground (SoCG) between SEW and NG, and an ‘in principle’ position with Natural England and the Environment Agency on the preliminary outline design for the reservoir interacting with the RCP, including the river diversion and associated landscaping and ecological mitigation strategy and ensure that both projects can continue to be developed to each party’s satisfaction, by mid- September 2015.

1.2 Scope of work

The overall scope of works is detailed in the Terms of Reference (NG revised April 2015 revision) and CTR 31 March 2015 agreed with SEW and National Grid (and as set out in Task Order DOC090415-09042015122817), and is outlined in the section above. The Stage 1a scope is further broken down in the Terms of Reference as:

Terrestrial Ecology  Terrestrial ecology - extended Phase 1 Habitat Survey,  Outline mitigation strategy including planting strategy - initial proposals.

Landscape and Visual assessment

A limited initial landscape and visual impact assessment (LVIA) will be undertaken in relation to the interaction of the RCP and the design of the reservoir. This will not constitute a formal LVIA, which will be the responsibility of each party to produce to support their relevant applications. This initial work will therefore inform the mitigation strategy including the planting strategy, the accommodation of WFD requirements and visual aspects affected by the interaction between the two projects. Stage 1a will include an initial baseline assessment, initial input to mitigation and planting strategy and commentary on the interaction between the two projects. It would also inform the basis for visualisations required in developing the reservoir scheme.

Cultural heritage

An Archaeological Desk Study to identify key risks and constraints and build in any mitigation that might be required. NG is to provide baseline information collected within their study area, which may reduce the study area data collection for the Broad Oak Reservoir assessment

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Geomorphology  Geomorphological reconnaissance survey  Preliminary WFD compliance assessment and geomorphological assessment for channel and fish pass design Aquatic ecology  Initial walkover survey and assessment of aquatic ecology requirements for the diversion channel and fish pass design Engineering

The following studies are required to understand the impact of the RCP route alignment on the future river diversion, dam and pipeline construction:  Topographical survey to provide existing river features and profile for design;  Sarre Penn river flow (HYSIM) and flood assessment, preliminary hydraulic design by hand calculation to define capacity and average bed slope along the different reaches;  Ground investigation (GI) scope provision and review of GI findings during the fieldwork for the river channel and dam right abutment (works to be carried out by NG GI contractor);  Geotechnical Interpretative report for the river diversion;  Geotechnical preliminary design of river channel, including assessment of potential water losses and hydraulic stability of side slopes;  Alignment of river channel corridor using conservative assumptions for geomorphological variability and bed and side slope stability;  Pipeline routing in the vicinity of the reservoir:  Initial assessment, based on desk study only, of embankment stability and foundation treatment requirements of the right abutment in the area of interface with the RCP; and.  Construction methodology for the components referred to above.

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2. Study Approach and Baseline Data

2.1 Previous studies

This study is to confirm the corridor required for all the reservoir components in the area of its interaction with the RCP and identification of potential conflicts. As such the study area has concentrated on a corridor that runs to the south of the reservoir. This corridor consists of the diverted Sarre Penne river and associated planting, access tracks and bridleways, dam right abutment, permanent access to the dam crest, and raw and treated water pipelines. These items, with the exception of the pipelines over part of their routes, have been kept to within the South East Water land ownership boundary, giving a study area between the top water level of the reservoir and the land boundary to the south.

Table 2-1 below presents the existing information that has been used in this study. The following sections present the new investigations that were conducted.

Table 2-1 Key data used

Reference Use

Atkins (2008) Broad Oak Reservoir Masterplan 1B, Drawing no. Drawing production, location plan 5044447/M/210, rev. P1. Atkins (2008) Broad Oak Reservoir Pipeline Plan, Drawing Pipeline design No.5044447/M/200, Rev. P2 Atkins (2008) Broad Oak Reservoir Exploratory Hole Location Geotechnical Plan, Drawing No. 5044447/C/257-8, Rev. C Map of proposed pipeline route Pipeline design Map of proposed incidents during wartime Cultural Heritage Atkins (2008) Broad Oak Reservoir As Built Exploratory Hole Geotechnical Location Plan, Drawing No. Figure 21, Rev. A South East Water (2009) Scheme Hold Briefing Note, Rev. Draft Background information V3 Feb09 Atkins (2008) Broad Oak Reservoir Pipeline Plan, Drawing No. Pipeline design 5044447/M/200, Rev. P2 Environment Agency (2015) Various strategic water resources Hydrology Atkins (2008) PR09 Option 30 Background information, pipeline design Jacobs (2008) South East Water Water Resource Management General Information, Pipeline Plan, Constrained Options Study design Jacobs (2012) South East Water Water Resource Plan, Surface General Information, Pipeline Water Screening Methodology. design Atkins (No Date) 0.5m Contours in AutoCAD format Drawing production, hydrology, river diversion National Grid Pylon Routes General information Historic maps (Old Maps, 2015) WFD and Geomorphology Contemporary OS maps WFD and Geomorphology Geological maps (BGS, 2015) WFD and Geomorphology Soil maps (Soilscapes, 2015) WFD and Geomorphology

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Reference Use

Maps of designated areas (Magic, 2015) WFD and Geomorphology Aerial photographs (Bing, 2015) WFD and Geomorphology National Character Areas, Natural England. Accessed 6th May Landscape 2015 Landscape Assessment of Kent (Kent County Council/Jacobs Landscape Babtie Oct 2004) Draft Canterbury Landscape & Biodiversity Appraisal (Canterbury Landscape CC/Jacobs, 2012) Canterbury District Local Plan Publication Draft 2014 Chapter 10 Landscape Landscape & Biodiversity Policy. Accessed 6th May 2015 The Stour salmonid monitoring programme report (Environment Aquatic ecology Agency, 2008) Atkins river corridor survey (2006) Aquatic ecology EA fisheries baseline data requirement for environmental Aquatic ecology assessment (2004)

Full study references are provided in the references list at the end the report.

2.2 Topographic survey data

An existing topographical contour plan prepared by Atkins for SEW was made available to Jacobs and this has been used for the drawings presented in this report. The source of the survey information used to develop this contour plan is not known and the accuracy is therefore uncertain. Background mapping data (roads, buildings etc.) shown on the drawings are from Ordnance Survey tiles. The existing surveys had no information regarding the cross sectional details of the existing Sarre Penn.

This current study is concerned with the river corridor to the south of the proposed reservoir. To create a better understanding of the current Sarre Penn, and to enable modelling of the existing river, Jacobs conducted a survey along the length of the existing river between Tyler Hill and to just beyond the location of the proposed main dam. To sufficiently survey the existing Sarre Penn, cross-sections were taken at a maximum spacing of 100m on the upstream end of the study area, decreasing to 25m spacing in sections were the river became more sinuous. The survey data has also been used to produce a longitudinal section of the existing Sarre Penn along the study area.

2.3 Geo-environmental assessment

2.3.1 Study area

A preliminary geo-environmental desk study was undertaken in support of the development for the reservoir, focussing on the vicinity of the right abutment of the dam, diverted river channel and pipeline route (adjacent to the dam). From historical records, the area is and has been open farmed land since the mid-19th Century. A preliminary ground investigation was also undertaken and is described in Section 2.3.6.

2.3.2 Geology

The geology of the area detailed on the British Geological Survey (BGS) Sheet No 273, indicates that part of the site is underlain by superficial head deposits which are present along the route of the Sarre Penn river. For the remainder of the dam and reservoir site, the superficial deposits are indicated as absent. The underlying bedrock, and at ground level in the absence of the superficial deposits, comprise the London Clay Formation, to a depth of approximately 23mBGL. Below the London Clay, the strata sequence comprises Harwich Formation,

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Lambeth Group, Thanet Sand Formation, with the top of the Upper Chalk formation at a depth of approximately 75mBGL.

2.3.3 Sources of information

The following sources of information have been used;  Landmark Information Group Envirocheck Report;  BGS 1:50,000 Sheet No 273 – Faversham, Solid and Drift;  BGS Onshore GeoIndex;  Factual Report on a Ground Investigation for Broad Oak Reservoir – Norwest Holst 2008.

2.3.4 Previous Ground Investigation

A ground investigation factual report issued by Norwest Holst in 2008, on behalf of Atkins for the Broad Oak Reservoir and pipeline route indicated that the following investigation has been completed:  19 No. cable percussive boreholes, to depths between 10.0m below ground level(bgl) to 25mbgl  6 No hand excavated inspection pits to between 0.5mbgl to 1.0mbgl;  17 No. machine excavated trial pits to between 3.5mbgl to 4.5mbgl;  25 No. window sample boreholes drilled to depths between 4.4mbgl to 6.0mbgl;  In situ hand vane tests in trial pits and window sample boreholes;,  13 No. in situ variable head permeability tests in four boreholes between 5mbgl to 21.3mbgl,  Installation of 16 standpipes in locations;  Geotechnical laboratory tests including classification, strength, odometer consolidation and soil re-use tests;  Chemical testing for concrete classification;  10 No. contamination suit of tests for metals  The factual report was available but no interpretative report has been found

2.3.5 Site Investigation 2015

A preliminary site walkover was undertaken by staff from Jacobs and the ground investigation contractor on 29th April 2015, to confirm the proposed locations and access for field investigation. The site work was undertaken in two stages; the four boreholes and 18 window samples between 11th and 15th May, followed by the 10 trial pits on 3rd and 4th June. The investigation included the following;  Four No. cable percussive boreholes, drilled to depths between 15.0mbgl to 20mbgl;  10 No machine excavated trial pits to 3.0mbgl, with in situ hand vane tests;  18 No. window sample boreholes to 5.0mbgl with dynamic probing (dynamic probe penetrometer) in each location;  13 No. in situ variable head permeability tests in boreholes between 2m.bgl to 16mbgl;  Installation of three standpipe piezometers.

2.3.6 Ground Conditions Encountered (during 2015 ground investigations)

Preliminary interpretation suggests that the ground conditions encountered during the 2015 ground investigations are in broad agreement with the BGS mapping and the 2008 investigation;  Made Ground to 0.25m to 0.55m - silty sandy gravelly Clay,

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 Cohesive Head Deposits - firm locally soft, orange-brown, grey mottled sandy silty gravelly Clay, between 0.4m to 4.30m thick,  Granular Head Deposits in six locations - dense orange-brown clayey Gravel, varying in thickness from 0.45m to > 2.3m,  London Clay varying between 0.80m to >10.0m thick - occasional upper weathered layer 1.00m to 6.40m of firm to stiff, orange-brown silty Clay with fine selenite crystals”, overlying “stiff grey silty Clay with fine to coarse selenite crystals”. The London Clay is absent a short distance downstream of the dam axis,  The Harwich Formation was encountered east of and near to the proposed dam axis - dense to very dense grey-orange, brown fine silty Sand,  The Lambeth Group - encountered near the dam axis, comprising very dense green-brown fine to medium Sand,  The Thanet Sand Formation - not encountered in the 2015 investigations  Groundwater was encountered in one 2015 exploratory borehole location, and three trial pits; at shallow depths ≈ 2.0m.bgl in the Head Deposits. No readings have yet been attained from the recently installed standpipe piezometers.

2.3.7 Geotechnical Laboratory Testing

Geotechnical laboratory testing of the 2015 ground investigation comprised classification, strength and particle size distributions. The tests had been scheduled but results were not available at the time of reporting. The factual outputs from this ground investigation shall be published when available and incorporated into the geotechnical interpretative report during study stage 1b.

2.3.8 Contamination Analysis Testing

Contamination analysis testing was undertaken on eight samples from across the site. A summary of the initial waste classification of soils identified during these investigations is given in Table 2-2. It is emphasised during the 2015 ground investigation that this classification applies only for material which may need to be disposed of. A “hazardous” classification does not necessarily mean that the material poses a risk to human health or the environment, but that, if it is excavated, is surplus to requirements (i.e. a waste) and requires disposal, it should be disposed at facilities permitted to accept hazardous waste. It may be possible to re-use such materials on site if they can be demonstrated to meet certain criteria (such as need for and suitability for use). This would require specific further assessment (such as a Materials Management Plan).

Table 2-2 Waste classification of soils

Sample Location Depth WM2* Waste acceptance criteria

BH1 0.5 Non-Hazardous Inert Landfill BH2 0.5 Non-Hazardous Inert Landfill BH4 0.5 Non-Hazardous Non-Hazardous Landfill BH5 0.1 Non-Hazardous Inert Landfill BH5 0.3 Non-Hazardous Inert Landfill BH5 1.5 Non-Hazardous Non-Hazardous Landfill BH5 3.5 Non-Hazardous Non-Hazardous Landfill BH5 6.5 Non-Hazardous Non-Hazardous Landfill * Environment Agency Technical Guidance WM2 Definition of Hazardous Waste May 2008.

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2.3.9 Risks from Contaminated Soils

Based on the soil sample analysis undertaken, there is no evidence of substantial contamination at the site. The potential risks to general site users, the environment and controlled waters is considered to be very low as it is unlikely that significant exposure would occur to the slightly elevated concentrations of contaminants detected.

2.4 Geomorphology and Water Framework Directive

2.4.1 Study Area

The study area encompasses the proposed reservoir, the Sarre Penn, and the associated tributary potentially impacted by the scheme. The upstream extent is at Tyler Hill and the downstream limit is Calcott. A catchment overview has also been undertaken of the Sarre Penn potentially directly affected by the project from the source (south of Dunkirk) to the confluence with the Great Stour (near Sarre).

2.4.2 Methodology

The Broad Oak geomorphological assessment is based on a combination of a desk study, which reviews the existing information of the scheme and study area, and a geomorphological survey to further develop the key baseline assessments and impacts of the scheme.

The desk study comprised a review of the existing water framework directive status and objectives for the Sarre Penn water body within the South East River Basin Management Plan (RBMP). Findings of the desk study are presented in Section 2.4.3. This included the following:  Historic maps (Old Maps, 2015)  Contemporary OS maps  Geological maps (BGS, 2015)  Soil maps (Soilscapes, 2015)  Maps of designated areas (Magic, 2015)  Aerial photographs (Bing, 2015) A geomorphological reconnaissance survey was undertaken by Jacobs on 15th April 2015. The survey assessed the baseline condition of the main channel within the catchment potentially affected by the proposed scheme. The survey provided an understanding of the existing geomorphological conditions of the water body and the condition of the channel upstream and downstream, where possible. A photographic record of the general character of the watercourse was collected. Findings of the geomorphological reconnaissance survey are presented in Section 3.4.3. The reconnaissance survey was of the reservoir footprint only and was not a fluvial audit of the entire catchment; as a result, the sediment sources upstream of the reservoir footprint were not determined.

2.4.3 Summary of Baseline Information

The main river within the study area is the Sarre Penn, which has its source approximately 9km upstream of the reservoir site to the west south of Dunkirk. The river then flows east through the proposed scheme footprint, and continues to a confluence with the Great Stour near Sarre approximately 10km downstream. The river is fed by a network of small drainage ditches (typically man-made) in the upstream extents and one main tributary near Vale Farm within the proposed scheme footprint. The Sarre Penn is a WFD water body, the Sarre Penn, S Chislet and Monkton Minsters Marshes (GB107040019620), which was classified as achieving Bad Ecological Potential in 2014 (EA, 2015).

A desk based assessment of the whole Sarre Penn catchment (see Figure 2-1 for survey extent) has been undertaken using aerial photography. The river is sinuous in the upper section west of Hersden (approximately 3km downstream of the reservoir), below which the river then appears to have been historically modified with a

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straightened planform and uniform channel (probably a result of dredging) continuing to a confluence with the Great Stour. In the lower section (downstream of Hersden) the river appears to be embanked for the majority of its length and a number of structures were observed, including weirs. There is a more natural riparian corridor in the upper section which is semi-continuous, but then is non-existent in the lower section with only a few scattered trees present. The adjacent land use is predominantly agricultural, with some lengths of woodland (most of which is ancient woodland and classified as a Site of Special Scientific Interest (SSSI). The upper section showed some evidence of erosion and deposition in the channel; however, the lower section was observed to be uniform with no such features evident.

Figure 2-1 Sarre Penn survey area

Within the study area, the Sarre Penn has a low to moderate gradient. The river upstream of Mayton Lane bridge (approximately 500m upstream of the dam crest), was observed to have a meandering planform, with evidence of actively eroding meanders. Further downstream of the bridge, the river was assessed to become more stable, with a uniform cross-section and straighter planform. Within the river corridor, a low flow channel was observed throughout the majority of the river, particularly across the shallower depositional features. The river typically got wider and deeper as it progressed downstream from Tyler Hill to Vale Farm. The river banks ranged from gently sloping to vertical (typically eroding) banks, ranging in height between 0.3 and 2m. The bank material consisted of clay, silt and earth; the bed substrate was predominantly coarse gravels with some cobbles, with the deeper pooled areas consisting of silt.

At the time of survey, the flow was observed to be low. There were multiple flow types evident, with the predominant flow type being a combination of both glide and run flow. Pool-riffle sequences were evident throughout, demarking deep and shallow areas, changes in gradient and deposition of coarse material within the channel. Within the study area, the Sarre Penn was observed to be typically an active channel, with erosion of the vertical channel banks. Typically the banks were being undercut, predominantly on sharp meanders where the banks were found to be steep. The channel was observed to be incised in some reaches. Some of the banks were found to be stabilised by tree roots, strengthening the banks and increasing resistance to erosion. Some evidence of slumping of the banks was also observed.

A number of point sediment sources were noted during the survey including field drains and outfalls. These have the potential to discharge fine sediments and pollutants such as fertilizers, pesticides and herbicides from agriculture, into the river.

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2.4.4 Limitations

The initial phase of the geomorphological assessment has been conducted using conservative (precautionary) estimates to establish the existing conditions and those of the conceptual channel design. These are reported with the outline engineering design in Section 3.2.

The broad critical discharge calculations have been compared with the hydrological information provided from the Calcott gauging station and the hydrology reporting for this scheme. It should be noted at this stage that the hydrological data has a high degree of uncertainty associated with it, particularly at lower flows. As a result the values generated within this study are considered to be indicative and will be updated as the hydrological information is further validated.

The cross-sections used within the analysis are based on a two-stage channel design with a specified low flow channel. The capacities and potential discharges are indicative only and the results could potentially change as the design is refined and altered locally for specific features (i.e. pool/riffle sequences).

2.5 Aquatic Ecology

The area covered by the desk study and aquatic ecology survey runs from Tyler Hill downstream to the confluence of the Sarre Penn with its tributary stream near Vale Farm.

2.5.1 Data Used

The aquatic ecology study aimed to develop the key baseline information to allow identification of potential aquatic ecology impacts of the scheme, to inform the scheme design and likely mitigation requirements. The following steps were undertaken:  Collation and review of baseline and desk-based information of the scheme, water body and catchment; and,  A walkover survey of the main channel in the vicinity of the scheme.

The desk study involved the review of existing information which was available at the time of writing. This included previous reports with data on river species – including invertebrates, fish and aquatic plants. Additionally, the WFD status and objectives for the Sarre Penn water body within the South East RBMP provided context for the available data.

Some previous reports relevant to the scheme were also reviewed. These included the following:  The Stour salmonid monitoring programme report (Environment Agency, 2008),  River corridor survey (Atkins. 2006)  Fisheries baseline data requirement for environmental assessment (Environment Agency, 2004)

Available data on invertebrates, macrophytes and water quality were supplied by the Environment Agency or downloaded from the Environment Agency Geostore database.

2.5.2 Survey undertaken

A walkover survey was carried out alongside a geomorphology reconnaissance survey, and individual ecological features of note were mapped alongside geomorphology features. There were 6 reaches defined within the scope of the survey length covered, which extended from Tyler Hill in the west to Calcott in the east.

The survey provided an understanding of the existing habitat types and conditions of the river in the area surveyed. A photographic record of the general character of the watercourse was collected. Findings of the survey are presented in Section 2.5.3 and in the survey report is provided in Appendix A.

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Figure 2-2 River corridor field survey reach locations

2.5.3 Baseline description

Physical habitat characteristics

The river’s physical character is described in Section 2.3.3 above. The river channel was noted to be predominantly lined with dense to semi-open scrub and trees that overhang and densely shade the channel. Erosional as well as depositional features are common within the channel, and as a result flow diversity is varied. There is a gravel substrate throughout, ranging in size from medium to coarse gravel with some cobbles, with siltation confined to river margins and pools.

Woody debris is a feature within the channel, with large branches and even some live trees growing within the channel area. This provides refuge areas for fish and invertebrates as well as an increase in flow diversity, which extends the range of species which may exploit the varied current velocities according to habitat preference. Additionally, mature trees which line the banks – especially in the upper reaches of the surveyed area, and their exposed roots form part of the bankside structure – providing not only refuge and habitat areas for river fauna but physical stabilisation of the banks which may otherwise be prone to collapse under spate conditions.

The lower sections (reaches 5 and 6 in Figure 2-2) of the surveyed area become more uniform, and lack a riparian zone or field buffer strips in places.

Overall, despite the river’s location close to many fields under arable land-use with minimal field edge buffer strips, the river exhibited some good habitat. There was good river morphology giving rise to good flow diversity, especially in the upper reaches, and a good gravel substrate, which would be suitable for trout spawning in terms of gravel size and general lack of fine sediment, which can pose problems for habitat quality.

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Macro-invertebrates

According to WFD classification tables, the Sarre Penn catchment was classified as ‘High’ for invertebrates. Data from EA showed a diverse range of invertebrate fauna within the Sarre Penn.

Habitat quality indices such as Lotic Invertebrate Flow Evaluation (LIFE) and Biological Monitoring Working Party (BMWP)1 support this statement. BWMP indices are designed to detect the impacts of organic pollution. For the Sarre Penn data, a BWMP total score of 78 was found, which is indicative of good quality habitat conditions but with some evidence of slight anthropogenic impacts.

According to EA data for the river, the LIFE index score was 7, which would be assigned to flow group III. This is indicative of intermediate flows according to LIFE indices.

The Environment Agency data also revealed a large number of specimens from the family Glossosomatidae, or cased caddis. The Glossosomatidae family contains two genera, Glossosoma and Agapetus. They are generally encountered in clean fast flowing rivers and are absent from still and polluted waters.

During the Jacobs walkover survey, one sample of submerged substrate (cobble) with cased caddis attached was taken back to the laboratories for identification purposes. Two specimens of the species Agapetus fuscipes were identified.

Agapetus fuscipes is a caddisfly that occurs in chiefly unimpacted rivers and can be a suitable indicator species for natural conditions. Its substratum preference ranges from coarse gravel to boulders and bedrock. The species copes with dynamic discharge events by maintaining a high population density and recolonisation of disturbed habitats from refuges. However, the vulnerability of the species depends on the life stage of the animals (e.g. the ability to migrate, the oxygen demand and the habitat requirements differ between instars). Although several adaptations to dynamic conditions, a high frequency of discharge peaks or a long period of drought can cause the population to decline. Once a population has totally disappeared from a river it will take the species a long time to recolonize the river because of its low dispersion capacity (Nijboer, 2004).

Overall, the walkover survey revealed that river habitat looked favourable for invertebrates with good flow velocities evident, despite low flow conditions at the time of survey. This was made possible due to the heterogeneity in the river bed with low-flow channels within the main channel confining some flows, coupled with pools and marginal refuge areas. A range of flow velocities was thus achieved which would cater for a range of flow tolerances and life cycle phases.

Macrophytes and riparian vegetation

During the survey, few in river macrophytes were identified. The dominant cover was blanketweed (Cladophora sp) especially in the upper reaches 1 and 2 where there was dense shading from riparian trees. EA data was not available for the reach in question.

Bank vegetation species consisted of trees and shrubs of ash, blackthorn, elder, oak and field maple. Undergrowth species varied from common nettle, lesser celandine, ferns, wood anemone, dog’s mercury and ivy in densely shaded areas, to nettle and bramble in the lower reaches where tree cover is sparser.

Fish

As mentioned above, there were extensive river bed gravels within the length of Sarre Penn channel, some of which were deemed suitable as trout spawning gravels, being of optimum size and relatively clear of fine sediment.

During the Jacobs survey, a trout pool of medium sized trout was spotted at reach 1 from the bridge (TR14668 69684). The average size of the trout within this pool was approximately15cm in length.

1 Biological Monitoring Working Party (BMWP)1 scoring system is a method of assessing water quality using the families of insects - e.g. mayflies and stoneflies - and other aquatic invertebrates such as freshwater shrimps present in a river. Species are allotted points to rank their importance in the ecosystem, the less tolerant a group of invertebrates is to pollution the higher the points they are allotted.

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Additionally, a number of small trout parr were spotted within pools on reach 2. Figure 2-3 below illustrates a trout parr (1+) resting within a pool in the channel.

Figure 2-3 Trout parr (juvenile- within its first year) visible in centre of image

A recent fish survey was carried out by the Environment Agency (May 2015) at two sites within the specified survey area. The first site was at Tyler Wood (TR1545861237) and the second at Brookside (TR1623861913). Both sites revealed brown trout, European eel and bullhead. Smoltifying brown trout were also found and indicate that these individuals are changing form in readiness for downstream migration. This is important in the context of catchment connectivity and the retention of such within the scheme plans. It is thought that connectivity (in an upstream direction) from the sea to the Sarre Penn is currently impeded in a number of places downstream of the reservoir scheme boundary, and these obstructions (usually weirs or tidal gates) are outside the scheme area and the scope of the study.

Habitat requirements of brown trout and bullhead are similar in that medium to coarse gravel substrate is necessary for at least one of their life stages.

Coarse substrates with large stones appear essential for bullhead breeding and medium to coarse gravel for trout spawning. Shallow, stony riffles are utilised by juvenile bullhead, whereas sheltered sections created by woody debris, tree roots, leaf litter, macrophyte cover or large stones, are preferred by adult fish, at least during daylight. Adult trout utilise large pools as refuges and when low flow conditions affect a river, they can survive for long periods within a pool, provided it has sufficient shading to ensure temperatures remain cool enough (below around 20°C) and to provide cover from predators. In times of high flows, all age classes are likely to require slack-water refuges.

From the brief walkover survey, evidence from examining substrate suitability for spawning, coupled with these fish sightings would indicate that the river is potentially used by a wide age-range of brown trout. As such this is a valuable habitat for salmonid populations in the area.

2.5.4 Limitations

Due to the nature of the walkover survey, in-depth data of species assemblages was not collected and thus this study represents a high level overview of habitat quality along the reach of Sarre Penn which would be affected by the scheme.

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2.6 Terrestrial ecology

2.6.1 Study area The extended Phase 1 Habitat Survey area comprised the agricultural land within South East Water’s (SEW) landholding that would likely be affected by the proposed Broad Oak Reservoir development, including habitat enhancement works. The survey area did not encompass the entire SEW landholding and excluded large blocks of woodland within SEW’s ownership (see Appendix B Extended Phase 1 Habitat Survey Report for detail of survey area).

Biodiversity and environmental information, including records of the presence of statutory and non-statutory wildlife sites, protected species, and species of principal conservation importance within 1km (5km for bats) of the site, was provided by Kent and Medway Biological Records Centre.

2.6.2 Data used

In addition to data obtained by Kent and Medway Biological Records Centre, other sources reviewed during this study include internet based resources (e.g. MAGIC, Natural England SSSI citations), and survey reports provided by South East Water and the National Grid relevant to the Broad Oak site, including:  Atkins (2006). Mid Kent Water, Ornithological Survey Scoping Study, Strategic Water Resources Investigation, Draft report, November 2006.  Atkins (2007). South East Water Strategic Water Resources Investigation, Passage Bird Survey 2007 Report.  Atkins (2007). Mid Kent Water, Terrestrial Ecology Preliminary Scoping Study, Strategic Water Resources Investigation, Draft report, June 2007.  Atkins (2008). South East Water, Terrestrial Ecology Scoping Study, Broad Oak Reservoir – Proposed Rising Main, Draft report, September 2008.  Kent and Medway Biological Records Centre (2015), Broad Oak Reservoir, Ref, ENG/15/202.  Lee Donaldson Associates (2006). River Corridor Survey of selected sections of the Sarre Penn, Wantsum, Whitfield Sewer, North Stream, Great Stour and Stour.  National Grid (2014). Richborough Connection Project, Proposed South East Water Reservoir, Route Options Appraisal.  National Grid (2015). Document 3.8 Trees and Hedgerows to be Removed or Affected Plans, National Grid (Richborough Connection Project) Order.  National Grid (2015). Document 3.10. Habitats of Protected Species, Important Habitats or Other Diversity Features and Waterbodies in a River Basin Management Plans. National Grid (Richborough Connection Project) Order.  Natural England (2013) [Online]. Local Nature Reserves: Tyler Hill Meadow, http://www.lnr.naturalengland.org.uk/Special/lnr/lnr_details.asp?C=0&N=&ID=857, Accessed 26th May 2015.  Natural England (2015) [Online]. Citation: West Blean and Thornden Woods, http://www.sssi.naturalengland.org.uk/citation/citation_photo/1003346.pdf. Accessed 26th May 2015.  Natural England (2015a) [Online]. Planning and development – guidance. Ancient Woodland and Veteran Trees: protecting them from development, https://www.gov.uk/ancient-woodland-and-veteran-trees- protection-surveys-licences, Accessed 27th May 2015.  Newcombe, M. (2008). Proposed Broad Oak Reservoir, Broad Oak, Canterbury, Kent: Badgers, 30th October 2008.

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2.6.3 Survey undertaken

The extended Phase 1 habitat survey was undertaken in accordance with standard guidelines described in Handbook for Phase 1 Habitat Survey – A Technique for Environmental Audit; Joint Nature Conservation Committee (JNCC, 2010). Target notes were made where applicable and included recording the locations of habitats that could be used by legally protected species.

2.6.4 Baseline description

The majority of land within the survey area (approximately 68%) comprises arable fields supporting agricultural crops. Woodland habitats account for approximately 22% of the habitat within the survey area. Grassland is limited within the survey area with fields of poor semi-improved or improved grassland and narrow grassland verges along some of the access tracks accounting for just 7% of overall habitats. The Sarre Penn river and one of its tributaries flows from west to east across the site before merging to form a single channel at Vale Farm; the riparian corridor includes broadleaved woodland and scrub, especially in the river’s upper-reaches. Other types of habitat accounted for less than 5% of the survey area, and include an intensively managed orchard, hedgerows and localised or very small areas of tall ruderal vegetation, scrub and standing water (Appendix B).

The desk study confirms the presence of one Site of Special Scientific Interest (SSSI), one Local Nature Reserve, four Local Wildlife Sites, and several blocks of ancient woodland within 1km of the proposed reservoir (search radius centred on Ordnance Survey grid reference TR 158 618); of these sites, West Blean and Thornden Woods SSSI, Little Hall and Kemberland Woods and Pasture Local Wildlife Site, and two blocks of ancient woodland (excluding the ancient woodland covered by SSSI and Local Wildlife Site designations) are located within SEW’s landholding. Of the above sites, the West Blean and Thornden Woods SSSI and areas of ancient woodland are located within or immediately adjacent to the footprint of the proposed reservoir.

The presence of a variety of protected and notable species has been recorded within 1km of the proposed reservoir footprint, although given the limited diversity of habitats recorded within the area likely to be affected by the proposed reservoir the potential presence of many of these species can be discounted due to the unsuitability of the on-site habitats. However, hedgerows, woodland, mature trees, buildings, riparian and arable habitats do have the potential to support a variety of protected or notable species including bats, great crested newts, dormice, reptiles, breeding farmland birds, water voles, invertebrates and brown hare.

Further habitat and protected species information is provided in the extended Phase 1 Habitat Survey report in Appendix B.

2.6.5 Limitations

The Phase 1 Habitat Survey area did not encompass the entire SEW landholding and excluded large blocks of woodland within SEW’s ownership as these can be mapped using aerial photography and a detailed assessment of these habitats is not considered necessary at this stage in the scheme; furthermore, as all of the surrounding woodland is designated as a SSSI, a significant amount of existing baseline information is available that the results of a Phase 1 habitat survey is unlikely to add to.

It is not within the scope of this document to provide a detailed ecological impact assessment or mitigation proposals. However, a summary of the main anticipated impacts and likely outline mitigation measures are provided.

2.7 Landscape and visual

2.7.1 Study area

The study area for landscape and visual effects is broadly defined by the extent of visibility of the proposed reservoir scheme.

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To the north it is enclosed by the wooded ridge of The Blean SSSI, notably Thornden Wood and West Blean Wood. The woodland wraps around to the west towards Tyler Hill where the study area is defined by Hackington Road. To the south it is defined by the ridge running from south of Tyler Hill through Little Hall Farm through to Broad Oak village. To the east it is generally contained by vegetation along and to the east of the A291 Herne Bay Road.

Landscape designations and character areas adjoining and abutting this area have also been considered to provide context and are discussed in section 4.5 in terms of potential impacts.

2.7.2 Data used

The following publications have been reviewed, alongside reports provided by South East Water and the National Grid relevant to the Broad Oak site:  National Character Areas, Natural England http://publications.naturalengland.org.uk/publication/2900242?category=587130; accessed 6th May 2015  Landscape Assessment of Kent (Kent County Council/Jacobs Babtie Oct 2004)  Draft Canterbury Landscape & Biodiversity Appraisal (Canterbury CC/Jacobs 2012 https://www.canterbury.gov.uk/media/519663/CanterburyLandscapeCharacterBiodiversityAppraisalDraftAu gust2012lowres.pdf  Canterbury District Local Plan Publication Draft 2014 Chapter 10 Landscape & Biodiversity Policy http://canterbury- consult.limehouse.co.uk/portal/cdlp_2014/cdlp_publication_2014?pointId=1394624366172#section- 1394624366172; accessed 6th May 2015

2.7.3 Survey undertaken

A desktop survey has been undertaken to review landscape policy and designations applicable to the scheme, along with relevant national, regional and local landscape character assessments.

A field survey was undertaken on the 23rd April 2015 to verify landscape character descriptions and identify key landscape features and elements. Potential viewpoints and visual receptors were identified by visiting key settlements and walking the public rights of way.

2.7.4 Baseline description

Broad Oak valley is a rolling arable landscape with rounded slopes, divided into two distinct valleys, where narrow rivers cut west to east across the area. The most notable of these is the Sarre Penn. The area stretches from Tyler Hill in the west, north of Broad Oak and Sturry and is bounded by West and East Blean Woods to the north with a small area located in between the two woods.

To the south a wood and tree-lined ridgeline runs from south of Tyler Hill through to Broad Oak village. This ridge separates the Broad Oak valley from Canterbury to the south. Broad Oak village is located prominently on the ridge; however the orientation of the village is generally on or towards the southern slopes with relatively few properties to the north of Sweechgate with a northerly aspect and views over the study area. The village is largely surrounded by orchards enclosed by mature hedgerows and shelterbelts. Whilst orchards are a traditional feature in the landscape, the orchard trees themselves are commercial low height tree stock and are considered to be a transient feature in the landscape that cannot be relied upon for long term screening.

The field pattern is defined by a strong network of hedgerows and dense mature tree corridors along valley rivers. Arable farming is the primary function, with small isolated valley fields of rough grassland, east of Tyler Hill. Small scale mixed deciduous and coniferous woodlands, containing sweet chestnut and hazel coppice stands are scattered across the slopes. The networks of woodlands and hedgerows create a strong pattern and are valuable for wildlife. There is a strong sense of enclosure due to the dense mature woodland corridors and rolling topography and the edge of Blean Woods to the north. Thus views tend to be restricted. However, from higher points there are long views to the east and south over adjacent farmland.

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The A291 runs north-south to the east, along which are scattered mixed style residential and commercial developments. Elsewhere vehicular access is very limited with minor rural lanes and tracks leading to isolated farmsteads.

The landscape is in good condition with a good network of mature hedgerows and woodlands. Occasionally these hedgerows are fragmented along the lanes and have been supplemented with chestnut pale and post and wire fencing. Modern agricultural barns are built in unsympathetic materials, but generally well-sited in valleys. Other buildings are limited to a few farms and scattered houses. These are of mixed age and built from traditional red brick and have a low impact on the landscape.

Electricity pylons are prominently located crossing the valleys and ridgelines. UK Power Networks (UKPN) power lines run north to south through the study area and NG lines run to the west.

Potential visual receptors People who are likely to experience views of the reservoir include:  Residents of properties along the northern edge of Broad Oak village, including Mayton Cottages to the west of the village  Residents of properties in Calcott, particularly those on higher ground to the west of the A291 who currently enjoy views to the south west towards the Broad Oak ridge  A limited number of residents from Tyler Hill who currently experience views along the Sarre Penn Valley between Great Hall Wood and Little Hall Wood  Residents in scattered properties and farmsteads including in the vicinity of Mayton Farm in the centre of the study area and the area near Blaxland Farm to the north  Users of existing public rights of way  New users and visitors to the reservoir and its associated footpaths and cycleways.

2.7.5 Limitations

It is not within the scope of this document to provide a detailed landscape and visual effects assessment or mitigation proposals. However, a summary of the main anticipated impacts and likely outline mitigation measures are provided.

2.8 Cultural Heritage

2.8.1 Study Area

Based on guidance provided in HA208/07 the study area has been defined as the boundary of land owned by South East Water and an area extending 500m in all directions from it.

The design corridor comprises a zone within which the final location of elements of the proposed scheme is not yet confirmed and an area of interaction between these elements and the National Grid pylon alignment.

2.8.2 Data Gathering

To inform the cultural heritage baseline for the study area, the following sources of information were consulted:

 The National Heritage List for England for information on designated cultural heritage assets;

 Kent County Council Historic Environment Record for information on archaeological sites, historic buildings and historic landscape characterisation data;

 Canterbury City Council website for information on Conservation Areas; and

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 Jacobs, October 2014, Broad Oak Storage Reservoir Concept Plan Stage 3, Landscape Ecology and Recreation Briefing Notes.

2.8.3 Assessment undertaken

An assessment of the value of cultural heritage assets identified from the sources listed above was undertaken on a six-point scale of Very High, High, Medium, Low, Negligible and Unknown. This assessment was based on professional judgement guided by criteria provided in HA208/07. The assessment is described in more detail in Appendix E.

2.8.4 Baseline description

From sources identified above a total of 17 designated cultural heritage assets have been identified within the study area comprising 17 cultural heritage assets within the ‘Historic Buildings’ sub-topic, two of which are Conservation Areas and 15 are Grade II Listed Buildings. These assets are listed below.

Asset No/ Asset Name /designation type 1 Tyler Hill House Grade II Listed Building 2 Tyler Hill Cottage Grade II Listed Building 3 Taylors Cottages Grade II Listed Building 4 Wayfair Grade II Listed Building 5 Tyler Hill Conservation Area 6 Allcroft Grange, Hackington Conservation Area 7 Blaxland Farmhouse Grade II Listed Building 8 Vale Farmhouse Grade II Listed Building 9 Summer Hill Grade II Listed Building 10 124 Sweechgate Grade II listed Building 11 Royal Oak Public House Grade II Listed Building 12 Mead Manor Grade II Listed Building 13 Broad Oak Grade II Listed Building 14 Stable Block at Farm Grade II Listed Building 15 Barn at Sweech Farm Grade II Listed Building

2.8.5 Limitations

This study is informed by a desk-based analysis using sources identified above. No walkover survey, non- invasive survey or invasive archaeological fieldwork has been undertaken as part of this study.

2.9 Hydrology

2.9.1 Scope

Hydrological data is required to inform the design of Broad Oak reservoir and appurtenant works, including the diversion channel. The hydrological work carried out provided information and data to facilitate the geomorphological and hydraulic design of the diversion channel in Stage 1a and to provide input for the reservoir yield assessment to be carried out in Stage 2 of the study. The two hydrological activities included in Stage 1a of the study were:  To generate flood peaks for return periods in the range 2 to 100 years for use in the design of the river diversion channel and fish pass; and

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 Undertake water resource modelling of the Sarre Penn river to feed into the by-pass channel design and allow a future estimation of the reservoir yield to be calculated.

The objectives of the water resources modelling were:  To review the flow data available for the Sarre Penn as recorded by the gauging station at Calcott for use in calibrating the rainfall-runoff model;  To develop a reliable time series of daily mean flows in the Sarre Penn river using the HYSIM rainfall-runoff model;  To provide flow-duration curves for the Sarre Penn at the gauging station at Calcott and at the intake to the diversion channel; and  To identify any shortcomings regarding the flow data that may impact on the design of the diversion channel and other facilities and make appropriate recommendations for future action to resolve these issues.

The time series of mean daily flows generated by the Hydrological Simulation (HYSIM) model will be used in a following stage of the study as input to a reservoir simulation model for evaluating the yield of Broad Oak reservoir taking into account natural inflows to the reservoir, spills from the diversion channel during flood events and the operation of the pumping station at Plucks Gutter and the pipeline transferring water from the river Stour to the reservoir.

2.9.2 Study area

The Sarre Penn catchment (Figure 2-4) considered in this assessment is approximately 19.6km² in area, lying to the north of Canterbury, Kent. The underlying geology is impervious, composed of London Clay, covered with loamy / clayey brown soils (refer to section 2.3 for further detail of geology of the site). The catchment is predominantly rural with land cover comprising a mixture of woodland, arable or horticultural, and grassland, with a small proportion that is urbanised. The elevation across the catchment ranges from 20–120mAOD.

There are two main tributaries to the Sarre Penn river. The southern tributary flows in a north-easterly direction from its source south of Dunkirk, under the A2, passing the villages of Blean and Tyler Hill down to Calcott. The northern tributary rises to the north-east of Blean and also flows in a north-easterly direction before converging with the southern channel at the New Vale Farmhouse (Figure 2-4). From here the Sarre Penn continues to flow to the north east under the A291 and onward until it flows into the Great Stour river. There is an Environment Agency river flow gauge at Calcott (40027) just downstream of the proposed dam site.

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Figure 2-4 Location of Sarre Penn Study Catchment

2.10 Flood study

2.10.1 Approach

The approach adopted for determining design floods of the Sarre Penn was based upon the use of the FEH statistical pooling group method which is considered best practice in the UK, with a supplementary check made using the Revitalised Flood Hydrograph (ReFH) method.

2.10.2 Data used

The use of the statistical pooling group method involves two steps: the development of the Median Annual Flood (QMED), equivalent to a flood with a return period of 2 years at the site of the Sarre Penn gauging station; and the development of a flood growth curve to allow the calculation of flood peaks with return periods in the range 2 to 100 years.

In the absence of reliable flood peak data from the gauging station, the QMED value was derived based upon catchment descriptors taken from the FEH CD-ROM and a correction factor was developed based upon data from donor gauging stations in the region: 40003 (R. Medway), 40005 (R. Beult) and 40010 (R. Eden). The correction factor was found to be 1.0.

A pooling group of 14 gauging stations was developed to determine the flood growth curve, with a total of 512 years of annual maximum flood data. The resulting flood growth factors are shown in Table 2-3.

2.10.3 Results

The QMED value at the Sarre Penn gauging station was found to be 3.02m3/s; the flood peaks derived by application of the flood growth factors for return periods in the range 2 to 100 years are given in Table 2-3.

A check on the flood peaks was carried out using the ReFH method. This involved the use of catchment descriptors for the location of the Sarre Penn gauging station downloaded from the FEH CD-ROM and the ReFH model as implemented in the ISIS simulation program. The results are also shown in Table 2-3 for comparison. The ReFH flood peaks are comparable but on average about 20% lower. Based upon this the results provided by the pooling group analysis were accepted as conservative values.

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Table 2-3: Flood growth curve factors and associated flows for the Sarre Penn at Calcott Return Period 2 years 5 years 10 year 20 year 50 years 100 years (QMED) Growth Factor 1.00 1.44 1.77 2.27 2.72 3.24 Statistical Method 3.02 4.35 5.36 6.87 8.23 9.81 Flow (m³/s) ReFH Flow (m³/s) 2.65 3.54 4.26 5.02 6.23 7.36

The flood peaks presented in Table 2-3 are derived for the Sarre Penn at the gauging station. Flood peaks as inflow to the diversion channel can be determined by scaling on the basis of catchment area. The flood peak at the inflow to the diversion channel will depend upon the catchment area at the location of the diversion point on Sarre Penn, which remains to be finalised. The scaling factor ranges from 0.43, for the most upstream location at Tyler Hill, to 0.59 immediately upstream of the confluence with the northern tributary. An additional allowance should be made for the catchment area of the by-pass channel itself.

2.10.4 Limitations

The data from the Sarre Penn gauging is considered too unreliable to be used for flood peak analysis. If the accuracy of the flow data from the gauging station could be improved, it may be possible to derive a site specific assessment of QMED as confirmation of the value derived from catchment descriptors and donor transfer.

2.11 Water resources modelling

A full description of the water resources modelling work carried out is provided in Appendix C.

2.11.1 Gauging station review

Calcott flow gauging station was built in 1975 originally by Mid-Kent Water who operated the historic Flat-V weir until it was handed over to the Environment Agency to continue monitoring the site in the 1990s, monitoring ceased in 1996 when the station was discontinued. The station was revived in 2006 with the installation of a Sarasota 200 multi-path time of flight ultrasonic in-line system, with 4 paths, immediately upstream of the weir which has been retained. The current measuring section is considered capable of containing all but exceptional floods.

The hydrometric data available for this study is summarised in Table 2-4.

Table 2-4: Summary of available hydrometric data for the Sarre Penn at Calcott (40027)

Instrument Water Level (m) Flow (m³/s)

15 minute Mean Daily 15 minute Mean Daily Frequency Shaft Encoder 11/04/2007 – 26/05/2015 31/05/1981 – 25/05/2015 - - Flat-V theoretical - - - 16/02/1975 – 08/06/1996 Ultrasonic - - 15/08/2006 – 11/06/2015 15/08/2006 – 27/05/2015

The flow data available for this site is characterised by a low baseflow and rapid responses to rainfall, as would be expected from a predominantly clay catchment.

In general, the quality of the flow data available from a gauging station is established by comparison with a programme of flow measurement by spot gaugings which are used to define stage-discharge curves for weirs and to confirm the accuracy of ultrasonic gauges such as the Sarasota 200.

There is no spot gauging data available for the period of record from 1975 to 1996. This means that the accuracy of the flow data available for this period is unknown.

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Ten spot gaugings were completed between 2006 and 2010 to check the accuracy of the ultrasonic instrument, however, due to a lack of data from the ultrasonic only three were considered suitable for use in the comparison. These comparisons indicate that the ultrasonic appears to under-record in low flow conditions.

Examination of the flow data from 2006 to 2015 indicated numerous periods of very low or zero flow which is thought to be due to under-recording by the ultrasonic instrumentation, as identified from the limited spot gauging data. This is likely to be due to low flows corresponding to velocities at or below the minimum threshold for accurate measurement by the Sarasota 200 installation at this site. The gauge may be more accurate at higher flows, but there is no spot gauging data to confirm this.

The Environment Agency undertook a review of the gauging station in 2012 the outcome of which indicated that the gauged record should be used with caution across all flows Table 2-5. The review listed seven actions to be undertaken to improve the confidence in the gauging station; many of which are still outstanding.

Table 2-5: Calcott Gauging Station Data Quality Scores Flow Range High Flows Low Flows General (Mean) Weighted Score* 0.50 0.46 0.28 Data Use Classification Caution Caution Caution * 1 = best quality, 0 = worst quality

2.11.2 Rainfall-runoff modelling

The HYSIM catchment rainfall-runoff model was used to develop an extended time series of daily flow data as inflow to the proposed Broad Oak Reservoir and for use in the design of the diversion channel. HYSIM is a hydrologic simulation model which uses mathematical relationships to determine the runoff from precipitation and potential evapotranspiration data and was used in this study to simulate flows in the Sarre Penn at the gauging station. The model has a number of parameters, for hydrology and hydraulics, which define the river basin and channels, and comprises a linked set of storage components with further parameters to define maximum rates of transfer between them and to characterise the equations which govern the transfer processes.

To use the model, parameter values need to be estimated. A first estimate is obtained by a study of the catchment type and this is later refined by optimisation of a few of the most sensitive parameters to minimise the difference between the recorded and the simulated flow. Once the model has been calibrated, it can be used to simulate runoff over extended periods from precipitation and climate data. The precipitation data was provided by the rain gauge at the Canterbury Sewage Treatment Works, for which daily data is available back to 1897. The potential evapotranspiration data was provided by the Environment Agency’s Stour Soil Moisture Model.

The model was calibrated against flow data from the gauging station between January 2012 and March 2015 inclusive and then verified using the optimised model parameters against flow data for the period 2007 to 2010.

Overall the calibration was considered to be reasonable given the known uncertainty with the gauged record and difficulty simulating low and zero flows. There are both over- and under- simulations of flows but the rates of recession are generally replicated and the overall water balance achieved. Comparison across the entire flow range using the flow duration curve shows a reasonable fit with a slight under estimation at the extreme low flows.

The calibrated model was then used to simulate the river flows over the period of record available for the climatic data; 1920 to 2015. The flow duration curve for the extended series is presented in Figure 2-5 and compared with the equivalent statistics published on the National River Flow Archive Table 2-6.

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Table 2-6: Statistical flow summary (in m3/s) for Sarre Penn at Calcott, as recorded on the National River Flow Archive and as derived from the simulated time series, 1920-2015

Percentile QMean Q10 Q50 Q70 Q95 NRFA 0.094 0.249 0.024 0.009 0.001 Simulated: 1920-2015 0.105 0.291 0.029 0.010 0.000

Figure 2-5 Extended simulated time series Flow Duration Curve – 1920 to 2015

10.000

1.000 (m³/s)

Flow 0.100 Daily

Mean

0.010

0.001 0 102030405060708090100 Percentage Time Flow Exceeded (%)

2.11.3 Limitations

The model calibration and subsequent simulation of flows are affected by the accuracy of the available flow data from the Sarre Penn gauging station; the high flows are likely to be more accurate than low flows. The gauging station is known to under-record at low flows which is likely to affect recorded flow data up to Q50 or more. Given that the HYSIM model has been calibrated against this data, the simulation time series will also under- estimate low flows.

There is a need to improve the quality of the recorded flow data followed by revisiting the HYSIM modelling and undertaking a model recalibration and re-simulating the extended flow series.

The flows generated by the simulation model are likely to be more accurate for high flows, however these represent mean daily values. Instantaneous flood peaks are likely to be higher than the mean daily peak values because of the responsiveness of the clay catchment. The magnitude of the difference between instantaneous and mean daily peak flows and the impact of the flow-duration curve remain to be assessed.

The following conclusions relate to the accuracy of hydrological data used as design criteria in Stage 1a to date and in the forthcoming Stages 1b and 2 of this study.

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Flood peaks

The flood peaks for return periods in the range 2 to 100 years were derived based upon the best method available and are considered to be suitable for purpose. These flood peaks relate to instantaneous values of flow and are unaffected by any concerns relating to the calibration of the gauging station on the Sarre Penn at Calcott.

Sarre Penn gauging station at Calcott (40027)

Data from the gauging station on the Sarre Penn at Calcott is available for two periods, 1975-1996 and 2006 to 2015 and is of variable quality.

The accuracy of the data collected between 1975 and 1996 when a flat-V weir was in use is not known as the data underlying the stage-discharge curve used for converting observed water levels to flows is not available. No spot gaugings from this period are available and flows above 1.7m3/s were truncated because of concerns regarding the weir being drowned during high flow events.

In principle, the data collected since 2006 following the installation of a multi-path ultrasonic flow meter at the gauging station is of higher quality. However, the dimensions of the measuring section, as entered into the software are known to be incorrect and the limited spot gauging data available (only three reliable spot flow gaugings) indicates that the instrument under-records at low flows up to about the Q50 flow. The significance of the errors involved cannot be established without a programme of spot gaugings. Environment Agency undertook a review of this gauging station in 2012 and identified a programme of actions necessary to improve confidence in the data available from this site, however it is understood that most of these remain to be implemented. No spot gaugings have been carried out at this site since 2010.

Rainfall-runoff modelling

An extended sequence of mean daily flow data from 1920 to 2015 has been generated from a calibrated HYSIM rainfall-runoff model using precipitation data from a raingauge with a long record and potential evapotranspiration data. It is acknowledged that the confidence in the representativeness of this simulated series is affected by gauging station data reliability.

Flow-duration curve

Flow duration statistics are provided for the observed flow data, as recorded in the National River Flow Archive for the Sarre Penn gauging station, and as derived from the simulated time series of daily flow data from 1920 to 2015 produced by modelling. Both sets of statistics are affected by concerns regarding the accuracy of low flow estimates as recorded by this gauging station. In particular there are significant doubts regarding the occurrence and frequency of zero flows and the value of the Q95 flow. The statistics for flows above about the Q50 level are likely to be less affected. However, the statistics generated from the simulated daily flow time series are likely to under-represent flood peak values as instantaneous peak flows may be significantly higher than daily mean values in this responsive clay catchment.

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3. Reservoir outline design

3.1 Overall reservoir concept

Broad Oak is a proposed reservoir site near Canterbury which is included within the adopted SEW WRMP for 2010 and 2014. To pick up the points made by Natural England during the consultation on the June 2014 WRMP, a concept plan was developed for the reservoir in October 2014 for discussion (Jacobs, 2014). The concept plan is reproduced in Appendix G and formed the starting point for the further work described in this report. The principal engineering components of the reservoir scheme are described below with the ecological and landscape objectives discussed and developed in Section 4.

The reservoir is situated on the Sarre Penn river and is proposed to have a top water level of 36.0mAOD providing approximately 4.4Mm3 of storage volume. The main retaining structure of the reservoir is formed by an earthfill embankment with a crest elevation of 38.0mAOD (approximately 15.5m high above the river bed) providing 2m of freeboard. Two secondary embankments of similar crest elevation, one to the west and one to the north of the reservoir, are required to limit the reservoir area and prevent long term inundation of part of the West Blean and Thornton Woods Site of SSSI. The secondary embankment to the west will have a crest elevation approximately 5m high above the existing river bed.

The main source of water used to fill the reservoir will be from abstraction at Plucks Gutter on the River Stour approximately 10km to the east. The pipeline will be routed along the south side of the reservoir and discharge towards the upstream end of the reservoir to promote water circulation within the reservoir.

The reservoir will have a chute spillway on the northern abutment of the main embankment to discharge flood flows in the Sarre Penn safely. The reservoir draw-off works will comprise a free-standing tower in the centre of the valley housing the draw-off pipework, which will pass through the embankment in a culvert to the downstream toe and on to the water treatment works.

The water treatment works will be situated on relatively flat land just downstream of the main embankment. Once treated, the water will be transferred to the Blean service reservoir via a pipeline running along the south of the reservoir.

The Sarre Penn is the main watercourse that runs through the reservoir area and is a designated waterbody under the WFD. The reservoir will inundate a section of the watercourse and to minimise the impact on riverine processes, it is proposed to divert the river along the south side of the reservoir. This report only focuses on the reservoir components that will interface with the Richborough Connection Project which is proposed to pass over part of the southern side of the reservoir and dam abutment. The outline design of the following components has been developed in outline and is described in the subsequent sections:  Sarre Penn diversion  Dam embankment south abutment  Southern access to the dam  Raw water pipeline and discharge structure  Treated water pipeline

Consideration will need to be given to the working space, construction methods and plant required to construct the project together with mitigation of construction impacts. Further details of these are given in Section 3.2.6 for the construction of the Sarre Penn diversion and Section 3.3.5 for construction of the dam. This will be developed in subsequent stages of this project.

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3.2 Sarre Penn Diversion Outline design

3.2.1 Overall Engineering Concept

Broad Oak Reservoir will flood a 2.0km length of the Sarre Penn river between Tyler Hill in the west and Calcott in the east. This length of river supports fish such as Salmonids. To enable the river to continue to support this fish population it is proposed to divert the river along the southern side of the reservoir, past the dam embankment and to tie back into the existing river a short distance downstream of the dam.

If the river diversion was taken to the south of the existing river planform, it would pass through a 650m section of the West Blean and Thornden Woods SSSI. As a result of the concerns at the potential impact this could have on the SSSI, the river will be diverted from Canterbury Hill Road (Tyler Hill) to the north of the existing river planform and cross the secondary embankment at the western end of the reservoir. To provide sufficient driving head to pass across the secondary embankment and around the reservoir, the river diversion will require up to a further 1.8km of diverted channel upstream of the reservoir, resulting in a total loss of approximately 3.8km of the river’s length.

The capacity of the diverted channel will be determined principally by the geomorphology and aquatic ecology requirements to provide a suitable habitat for the fish population and suitable morphological processes. The upper section of the river diversion will be designed such that all but extreme flood events will be contained within the channel to the secondary embankment. At the secondary embankment excess flows not required for geomorphological and ecological requirements will be spilled into the reservoir. This has the benefit of reducing the frequency of short term flooding on the upstream side of the secondary embankment as well as increasing the yield of the reservoir and reducing pumping costs to both fill the reservoir and drain any natural runoff reaching the upstream toe of the secondary embankment. Part of the local catchment cut off by the river diversion will drain to the upstream toe of the secondary embankment where pumps will be used to maintain a maximum water level to reduce any short term inundation of the SSSI woodland to acceptable levels. The river diversion will consist of the following five components:  A diversion structure at the upstream end to divert flows into the new channel. This will be located downstream of the existing culvert under Wood Hill Road at a location to be determined.  A channel through the existing fields to convey flows to the secondary dam, which will be located just downstream of the existing reservoir/fishing pond.  A section of channel running along the axis of this secondary dam to take the diversion onto the southern bank of the reservoir. It will incorporate a spill structure to discharge excess flows into the reservoir, whilst allowing sufficient flow to pass forward to create an active river downstream.  A cutting to the south of the reservoir to carry the diverted Sarre Penn around the southern abutment of the dam. The invert level of the river will be below the reservoir top water level along this stretch.  A fish pass to take the diverted river at a steeper slope beyond the embankment right abutment mitre to tie back into the existing Sarre Penn channel.

The longitudinal profile along the existing river together with a range of possible gradients for the diverted Sarre Penn is illustrated in Figure 3-1. The gradient of the channels are described in the legend with the first figure representing the gradient from the diversion point to the secondary dam and the second from the secondary dam to the main dam. It is assumed at the moment that the gradient over the secondary dam will be 1:1000. Cross sections for the options shown in Figure 3-1 with solid lines are given in Appendix G.

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Figure 3-1 : Possible Sarre Penn Diversion Gradients

The engineering considerations and constraints which control the design for each of the elements described above are described in Table 3-1.

Table 3-1 : Engineering Constraints

Section of Works Constraints Comments

Diversion The upstream limit is the road culvert at Tyler Hill, Too shallow a slope may not Structure while ensuring that there is no increase in flood risk provide suitable stream energies to upstream. maintain the clean and potentially The downstream limit will be determined by the mobile river bed required. The minimum acceptable river gradient while providing further upstream the diversion point sufficient gradient to tie into the channel over the the greater the available head. secondary dam. Channel to The channel capacity should be sufficient to take Close to the base of the valley there secondary dam moderate flood flows to increase reservoir yield and is a risk that the channel may be reduce the amount of pumping. excavated into sand rather than The channel gradient should be sufficient to ensure clay deposits. Lining of the channel that the gravel bed remains clean with limited silt may be required to retain water in deposition. the channel. Channel Over The channel at this point must be high enough for An offtake following a route to the Secondary Dam the diversion to pass over the secondary dam and south of the secondary dam is not during high flows be above the reservoir water level possible as this would mean cutting to allow for excess water to spill into the reservoir. through the SSSI woodland.

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Section of Works Constraints Comments

Cutting to Main The river must be designed such that it is mobile From the existing geotechnical Dam and has sufficient flow to maintain clean gravels survey data it appears likely that the and prevent excessive siltation. The flow passed is river diversion will be excavated in dependent on the slope of the channel and the clay deposits through this stretch of geometry of the channels. The gradient of the the diversion. channel forms the main constraint. A steeper channel will require a deeper and therefore wider cut into the adjacent hillside, affecting a greater area of land. At the abutment location the river needs to be far This location is where the cutting enough into the abutment to ensure that is does not will be at its greatest depth and a interfere with the foundation of the dam. section through here is shown in Appendix G (No. 1010). This cutting becomes deeper and further into the hillside as the gradient of the river is increased. Fish Pass The channel for the fish pass must be located This fish pass options are described between the embankment mitre and the water in more detail in Section 4.3. treatment works.

3.2.2 Channel hydraulic design

A longitudinal section along the Sarre Penn, taken from the topographical survey is illustrated in Figure 3-2 This shows that the existing average channel gradient along the existing channel is approximately 1:180. Upstream, at Tyler Hill, the gradient is approximately 1:150, and slackens to around 1:300 at the downstream end.

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Figure 3-2 Gradients Along Existing Sarre Penn

An ISIS hydraulic model was constructed of the existing river, using the surveyed channel cross-sections. This showed that the majority of the river flows remain within the channel up to a flow rate of 8m3/s; in a few sections the river flowed out of channel at a capacity of around 5m3/s. The hydrological study estimated the peak discharges for a range of flood events (Table 2-3). This together with the estimated channel capacity indicates that the existing river is able to take between a 1:10 and a 1:50 year flow before flowing out of channel. This suggests that the existing river is incised with limited floodplain connectivity.

3.2.3 Geomorphological design considerations

As part of the Stage 1a process, the geomorphology assessment considers potential options for varying channel gradients and channel cross-sectional size and shape. This is to ensure that the channel proposed to be realigned would have sufficient stream power to transfer sediment (particularly sand and silt), rather than acting as a sediment trap (storage zone). Calculations of potential stream power and critical discharge have been undertaken for a number of scenarios of gradient and channel cross-section. Specific stream power is the energy dissipated per river width, against the bed and banks of a river channel.

The stream power calculations for the bankfull capacity of the existing channel cross-sections generally range from 15 to 45 Wm2. It should be noted that because of the incised nature of the river these could reflect a wide range of discharges from 4 to 45m3/s, whereas the dominant discharge is normally taken as the 1 in 2 year discharge is estimated to be 3m3/s. This suggests that stream power values towards the lower end of this range could be more reflective of the channel forming characteristics in this reach. The river was observed to be incising in a number of the reaches, which is likely to be a result of historical channel modification (i.e. channel straightening). The incised channel would lead to higher stream powers as the bankfull conditions are overestimated and the channel could have the capacity to hold larger flows than would be considered ‘natural’. A literature review suggests that to enable a channel to maintain a morphological diversity and channel adjustment, the stream power would typically be expected to be greater than 10Wm2 and that pool/riffle sequences could be present in channels with gradients in the range from 1:50 to 1:700.

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For the diverted river, the following gradients have been considered in this stage of the project: 1:200, 1:400, 1:600 and 1:1000. The cross section has been taken as a two stage channel, as shown in Figure 3-3, for the preliminary hydraulic analysis.

Figure 3-3 : Typical Section for Analysis

The stream power of indicative channel sections have been analysed for channels varying in width from 5m to 6.9m, for each of the gradients listed above. The stream power has been plotted against discharge for the existing river and indicative channel sections in Figure 3-4. This Figure suggests that slope gradients within the range of 1:200 to 1:500 could deliver a stream power of 10Wm2 or greater at the bankfull discharge.

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Figure 3-4 : Stream Power

As stated above, the existing average channel gradient is around 1:180. A number of scenarios for a design slope and cross-sectional size and shape have been considered, with the following conclusions (in all of the scenarios the same cross-sectional dimensions have been assumed):  1:200 – this slope would replicate close to existing channel conditions, with stream powers above 10Wm2 with the potential to move coarse to very coarse gravels.  1:400 – this slope would potentially allow fine sediment (sand and silt) and also coarse gravels to be transferred (the latter depending on cross-sectional size and shape and during bankfull flow conditions). Stream power reaches 10Wm2 around the dominant discharges.  1:600-1:1000 – this slope range would potentially allow fine sediment (sand and silt) to generally be transferred but is unlikely to move coarser gravels. The stream power values would be between 1 and 8Wm2 and indicative of a stable channel unlikely to replicate the existing conditions. It should be noted that the gradient ranges discussed above assume the same channel cross-section dimensions and are averaged over a diverted river and that the actual gradients would in practice be varied throughout to create the pool-riffle sequence. The cross-sections used for the analysis ranged between 5 and 6.9 metres width.

3.2.4 Channel planform and cross-section design

The channel planform as proposed for the concept design (to date) consists of a few meander features within the reaches of channel upstream and downstream of a secondary embankment. This is likely to be adjusted and formalised as the design develops, but would potentially incorporate some meander bends and include some of the features present within the existing channel. The proposed channel cross-section for the purpose of the concept design is a two stage channel design. A two-stage design would also create a more diverse river corridor with a low flow channel and a larger channel for (up to) bankfull flows. The low flow would maintain longitudinal connectivity of the river and a pool-riffle sequence would be created for morphological diversity.

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The conceptual design provides an initial corridor. As the design develops river cross-sections can be varied (e.g. symmetrical in a straight reach and asymmetrical on a bend) and more natural features created accordingly such as side bars and mid-channel bars and additional habitat features such as small backwaters and woody debris.

3.2.5 Stability of banks and excavations

The slopes for the river diversion have been initially assessed using typical soil parameters and assuming that the river diversion is cut into London Clay. No groundwater data is currently available. Based on these initial calculations slopes of 1:4 were found to be adequate, although for this calculation the groundwater table was assumed as 4m below ground level. The slope stability calculations will be reassessed with the new ground investigation data and groundwater levels from the standpipe piezometers in the next project stage.

3.2.6 Sarre Penn construction requirements

The construction requirements for the Sarre Penn diversion have not at this time been considered; however, particular aspects that will need to be considered are:

Table 3-2 Construction Activities

Item Construction Activities

Diversion Construction of weir to divert flow into the by-pass channel. Will require excavation and Structure general construction works. Possibly a concrete structure for durability. Diverted Sarre Excavation into valley sides to create the diverted river. May require some clay lining in Penn the upstream stretches. Likely to be sufficient clay in the downstream ends. Fish pass Details of fish pass still under consideration, but will require earthworks and lifting equipment.

The Sarre Penn diversion involves significant earthworks. A cut and fill balance has not been completed at this stage of the study. This will need to be completed at a later stage to estimate the amount of material that is excavated in the river diversion that may be suitable for use in the dam construction. The construction will be planned to limit the amount of material removed from site, or imported to it.

The construction of each of the areas listed above will require temporary works during the construction and this will need to be taken into account in establishing the overall footprint that will be required to implement the project. This will be evaluated in subsequent stages bull will consider the following:  Type, capacity and size of construction plant, including the required turning circle;  Working space for safe construction;  Routing of temporary haul roads;  Space for noise bunds and other environmental mitigation measures for construction nuisance

Access will be required along the diverted river for maintenance such as tree cutting. This is anticipated to be made along the bridleway which is proposed to follow along the diversion route.

3.2.7 Risks and uncertainty

An initial assessment of risks and uncertainty are taken as follows:

River Flow Data

Incomplete river flow data for existing Sarre Penn and high and low flow data that has been received would appear to be unreliable. Recalibration of the existing equipment and spot gauging and survey to be undertaken to validate the input. Refer to risk table in section 6.3.

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Geotechnical Information

Information on ground conditions is incomplete. This study takes into account preliminary findings of the ground investigation undertaken in Stage 1a of the study; however the interpretative report from this investigation was not available at the time of writing this report. The risk is that the depth of clay is not being suitable for the diversion resulting in some sections of the river needing to be lined. The geotechnical interpretative report is to be completed once final investigation data and laboratory testing is complete and used as design input to further works. Refer to risk table in section 6.3.

Topographical Data

The topographical data used, except for the Sarre Penn channel, were supplied to Jacobs from an unknown source, and has not been checked or verified. The location of the dam, extent of the reservoir, and location of the diverted Sarre Penn have been based on this contour data. The baseline contour maps should be validated against other topographic datasets to validate the topographic data and used as design input to further works. Refer to risk table in section 6.3.

3.3 Dam right abutment outline design

3.3.1 Introduction

The dam retaining the reservoir is proposed to be a zoned embankment dam using locally sourced earthfill material. Limited geotechnical information is currently available as described in Section 2.3. A preliminary assessment of appropriate slopes to assess the likely footprint of the dam has been made using precedent from existing dams of similar height and constructed from similar materials.

3.3.2 Dam crest level

A top water level, of 36mAOD indicated by the Terms of Reference for this study, has been taken as the upper practicable storage level for the reservoir.

Freeboard above the maximum storage level is required to prevent overflowing or wave overtopping of the dam crest during extreme flood events and avoid erosion damage to the downstream face of the embankment, which has the potential to lead to catastrophic failure of the dam. The total design freeboard at the dam site is therefore an assessment of the combined effects of flood magnitude, magnitude of wind and thus waves, the amount of wave run-up the dam upstream slope, and the uncertainties in these estimates. No analysis has yet been carried out to determine the appropriate value and we have adopted an initial estimate of 2m for the freeboard required, thus making an embankment crest level of 38mAOD. The river bed level at the downstream toe of the dam is approximately 22.5mAOD, giving an overall maximum height of around 15.5m.

In addition an allowance will be required for post-construction settlement of the embankment and its foundations. This will vary with the height of the embankment and is normally provided as a camber with a maximum value in the centre of the valley reducing to a nominal value or zero at the abutments. Since the area of prime interest is the right abutment interface with the Richborough Connection, the settlement allowance in this location will be assumed to be zero therefore there is no impact from settlement on the interaction.

3.3.3 Dam Foundation

Treatment of the dam foundation may be required for the following purposes:  Removal of low strength material to assure the stability of the embankment;  Removal or treatment in situ to reduce permeability and thus water loss from the reservoir  Removal to intercept land drains  Removal and replacement with suitable fill material to increase the hydraulic gradient under the embankment and reduce the risk of internal erosion

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The preliminary results from the ground investigation suggest that dam foundation in the right abutment is likely to consist of London Clay to a depth in excess of 10 metres. Such a material is likely to provide a suitable foundation for stability of the embankment and global watertightness of the reservoir without treatment, except as indicated below.

The upper part of the London Clay stratum may be weathered and fissured with a consequent risk of increases in the potential for internal erosion and seepage losses. Insufficient information is available from the recent ground investigation yet to assess this in detail. At this stage it will be assumed that a nominal 3m deep cut-off will be excavated in the foundation across the full width of the embankment core. This will also ensure that all land drains are located and removed from the core.

All topsoil and organic material will be removed from the shoulders of the embankment. To allow for the removal of land drains and local pockets of weaker material an average stripping depth of one metre will be assumed.

3.3.4 Dam Section

The dam crest will provide access to the draw-off works situated in the reservoir in the centre of the valley. The access road is assumed to be 4m wide with 0.5m wide verges on either side, giving a total crest width of 5m.

The dam section will comprise an impermeable core of selected high plasticity clay supported by shoulders of a broader range of clay materials. The nominal dimensions for this preliminary design will be taken as follows:  Level of top of core: 37mAOD; one metre above top water level  Width of top of core: 4m  Core side slopes: 10v:1h; hydraulic gradient at base of core of 0.5

The core will have an inclined filter on the downstream side to prevent loss of particles through internal erosion. Water collected by the filter will be discharged at the base into a drainage blanket covering the downstream foundation. This blanket will ensure that the downstream shoulder is drained and will also safely discharge any water seeping through the upper part of the foundations.

Insufficient information is currently available from the ground investigation to carry out a preliminary design of the upstream and downstream slopes of the dam. Outline and detailed design will be undertaken during the subsequent stages of the project. To provide a preliminary assessment for the current study a literature review of the slopes for existing similar dams in the locality using similar construction materials has been completed.

A summary of the typical profile of dams of similar height and construction are presented in Table 3-4 using information extracted from Dams in the UK 1963 – 1983 (British National Committee on Large Dams, 1983).

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Table 3-3 Characteristics of similar embankment dams

Location Max Surrounding Geology Construction Materials Core Foundation Description of Slopes Average Average Height Upstream Downstream (m) Slope Slope

(1 in x) (1 in x)

Wraysbury 17 Alluvial plain of Clay core carried through alluvium Minimum 3m into Downstream: 1 in 2.5 after 4.7 3.4 Thames Valley (2.5- into underlying London Clay, to a underlying London crest, with a 16m horizontal 10m thick). minimum of 3m. Gravel shoulders Clay. berm in the middle. Upstream: with clay core layers. 1 in 3 to 1 in 5, with intermittent horizontal berms. Queen 20 Alluvial plain of Clay core carried through alluvium Minimum 3m into Downstream: initial slope after 4.9 8.9 Mother Thames Valley (2.5- into underlying London Clay, to a underlying London crest 1 in 2.5, before a 1 in 20 10m thick). minimum of 3m. Gravel shoulders Clay. berm, followed by a 1 in 6 with clay core layers. slope. Upstream: 1 in 3 after crest, followed by a 6.7m wide berm, followed by a 1 in 6 slope. Ardleigh 23 London Clay. Clay core, with sandy gravel Downstream: slope 8.7 9.3 shoulder containing some clay. immediately after crest is 1 in 2.5, which falls to a 1 in 20 berm, with below a 1 in 3 slope. Upstream: 1 in 3 after crest, falling to a 1 in 20 berm, before a 1 in 8 slope leading into the toe. Alton 12.5 London Clay, overlain Clay core with sand and gravel Clay blanket under Downstream: 1 in 4 after crest, 31 25 by Crag deposits, shoulders. upstream shoulder falling to 1 in 6, before a 1in 16 glacial sands and with bentonite berm, which flattens to 1 in 50. gravels. concrete cut-off. Upstream: 1 in 4 after crest, falling to 1 in 6, followed by a 1 in 50 berm.

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Location Max Surrounding Geology Construction Materials Core Foundation Description of Slopes Average Average Height Upstream Downstream (m) Slope Slope

(1 in x) (1 in x)

Bough Beach 24 Weald clay, with Homogenous clay Key trench up to 8m Downstream: 1 in 4 after crest, 5 4.4 seams of relatively deep to prevent falling to 1 in 4.5. Upstream: 1 permeable leakage through in 5. fossiliferous limestone seams limestone. Bewl Beach 30.5 Alluvial deposits (silt Clay core, with sandstone Clay blanket under Downstream: 1 in 2.5 after 7.4 8.3 clay) up to 4m thick. shoulder. upstream shoulder crest, falling to 1 in 20, and Underlain by with concrete cut- below this 1 in 4. Upstream: 1 Wadhurst clay (1- off. in 3, before a 1 in 20 berm, 15m thick), which is followed by a 1 in 4 slope. underlain by Ashdown Sands. Arlington 24 Weald clay, after Shoulders and core are Weald Core carried a Downstream: 1 in 4. excavation of very Clay minimum of 1.5m Upstream: 1 in 5. weak alluvial material into foundation. up to 11m deep. Ardingly 21 Wadhurst Clay, Wadhurst Clay core. Shoulders: Core taken through Downstream: 1 in 5 slope, 9.1 9.61 overlain by Wells rolled clay fill. Extended Wells Sands into followed by a shallow berm. Sands (relatively shoulders: alluvium/clay fill. underlying Upstream: 1 in 3 slope after permeable). Wadhurst Clay crest, followed by a 1 in 20 berm, rising to 1 in 12, and below this 1 in 7.

1 Scaled from drawing

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Figure 3-5 Slopes of existing embankment dams in similar materials

B14000AG/BORStudy/801 - Rev 2 39 Stage 1a Study

The overall upstream and downstream slopes shown for the reservoirs in Table 3-4 are plotted against maximum embankment height in Figure 3-5. For preliminary design an overall slope of 1v:6h for both upstream and downstream slopes has been taken as appropriate for an embankment consisting of London Clay with a maximum height of 15.5m. In the centre of the valley, depending on the foundation condition, it may be necessary to reduce the slope to around 1v:8h. In the upper part of the valley, where the embankment is of reduced height it may be possible to increase the slope to around 1v:4h. At this stage it would be sufficiently conservative to assume an average slope of 1v:6h up to 10m embankment height and 1v:8h for greater heights.

Space along the downstream toe for construction of mitre drainage will also be required.

3.3.5 Dam construction and maintenance

Temporary works for dam construction will also need to be taken into account in establishing the overall footprint that will be required to implement the project. This will be evaluated in subsequent stages but will consider the following:  Type, capacity and size of construction plant, including the required turning circle;  Working space for safe construction;  Routing of temporary haul roads;  Space for noise bunds/barriers and visual screening

Space beyond the embankment footprint will be required for access for routine maintenance and possible future repairs. A minimum of 5m beyond the permanent works will be allowed for in line with requirements for plant and vehicles as required. The 5m allowance is based upon sound experience of undertaking such works.

3.4 Permanent Access

Permanent access is required along the crest of the main dam. From the south of the dam, this access is planned to be made by redirecting Barnet’s Lane. This will need to pass over the diverted Sarre Penn on a bridge over to the dam crest. The access track will then pass along the dam crest and off to the north and joining with Mayton Lane.

The bridge structure required will depend on the width of the final corridor and if there is sufficient space to pass the track down the side slopes of the river cutting. These are currently planned at 1:4 therefore the access track would need to be cut into the slope to form a shallower gradient.

The bridge will require abutments to be constructed, and the bridge structure itself will be constructed from precast / pre-tensioned concrete or from steel sections. This will require significant construction plant including large lifting plant. The bridge is currently shown adjacent to where the proposed National Grid pylons cross the river at the southern abutment of the dam. The overhead conductors will introduce a construction constraint and risk to construction safety, which needs to be investigated further in the next stage of works, however at this stage of the study and without further design work having been undertaken the view is that it would jeopardise the deliverability of the permanent access as currently envisaged; and are likely to jeopardise the likelihood of being able to construct the bridge in this location. Relocation of the access track, such that it crossed the river further to the west, and passing the access track between the reservoir and the diverted Sarre Penn, would result in the river diversion moving further south. This would result in larger excavation for the river, and more land being required for the river corridor. Refer also to risks table in section 6.3

Alternative access routes can be considered in subsequent stages of this project, however currently it is considered that access is required from both the North and South ends of the dam crest. The access bridge, and interaction with the route of the RCP, is identified in the risk table in section 6.3 as a key risk as the interface introduces a significant hazard which under the CDM hierarchy would best be eliminated or mitigated so far as is reasonably practicable..

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3.5 Pipeline outline design

3.5.1 Overview

There are three pipelines associated with the Broad Oak Reservoir. The first pipeline delivers raw water abstracted from River Stour at Plucks Gutter to fill the reservoir. The raw water intake pipeline is about 12.8km of approximately 1000mm diameter pipe.

The second pipeline is a short pipe that transfers raw water from the reservoir to the proposed water treatment works located about 400m east of the Broad Oak Reservoir. Treated water is pumped from the new treatment plant through the third pipeline, which is about 7.4km of approximately 600mm diameter pipe, to Blean Service Reservoir for distribution.

The raw water intake pipeline and treated water supply pipeline share a corridor south of the Broad Oak Reservoir as shown in Appendix G.

The focus of this study is the area close to the reservoir where there is a potential conflict with the proposed National Grid RCP. However to ensure that all factors have been considered a preliminary alignment of the entire route for the raw water intake and treated water supply pipelines has been made based on readily available data listed in Appendix H. A detail socio-economic analysis, site survey and ground investigation shall be carried out as the project progresses to validate the proposed routes.

The general layout of the area means that both pipelines will have to cross the planning corridor at two locations, at chainage 10,960 and 12,130 for the raw water intake pipeline, and at chainage 80 and 1100 for the treated water supply pipeline. To minimise the length of pipeline exposed to the power lines, the pipeline routes should be selected to ensure that these crossings are as close to perpendicular to the power line corridor as possible, given other constraints. This would be addressed in further design stages.

A detailed socio-economic analysis, site survey and ground investigation shall be carried out by SEW as the project progresses to validate the proposed routes.

3.5.2 Data Input

Data on the sensitive environment, parks, existing infrastructure, topography and geology is assembled to define proposed pipeline routes. A summary of data gathered, including the type of data and source is provided in Appendix H.

These data are collated on ARCGIS and used to define feasible pipeline routes.

3.5.3 Design Constraint

The design constraints in defining the pipeline routes are described in the sections below.

3.5.3.1 Reservoir Outlet and Rising Main Construction

Working in the proximity of overhead conductors poses a significant safety risk. Health and Safety Executive Guidance note GS6 states that work may be executed in the proximity of an overhead power line if there is no alternative, and only after the risks are assessed and found to be acceptable. The guidance also recommends that the power line operator shall be contacted for advice for any work within 15m of a line erected on steel towers. Extra precautionary measures may therefore be required when operating in the proximity of overhead power lines. This is likely to cause delays for the future reservoir construction work, and potentially increase the construction cost.

In addition, the electromagnetic field generated by the power line can aggravate corrosion on metallic pipes. The pipe material for the intake and supply water pipelines will be defined as the project progresses. However, if the pipe material for the proposed pipelines were to be metallic, a specialised cathodic protection system is required to maintain the structural integrity of the pipe. This would increase the operation and maintenance cost

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of the pipelines. Detailed design would consider the material selection against all constraints and select that best suited to the operational, environmental and geo-physical constraints including consideration of cathodic protection of metallic pipes. These considerations are for SEW to take into account when evaluating the pipeline design in later stages of design. References to papers covering this are:

1. Cathodic Protection Co. Ltd. PIPELINE CORROSION RISKS ASSOCIATED WITH A.C. VOLTAGES. Undated technical Note

2. Shwehdi M. H. and Johar, U. M. Transmission Line EMF Interference with Buried Pipeline: Essential & Cautions. Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN (ICNIR 2003)

Electromagnetic Fields and Our Health 20th–22nd October 2003.

3. Simon, Philip D. OVERVIEW OF HVAC TRANSMISSION LINE INTERFERENCE ISSUES ON BURIED PIPELINES.NACE International, 2010.

3.5.4 Background Inputs

3.5.4.1 Environmental

The area from Blean to Broad Oak up to Plucks Gutter along the proposed pipeline routes is characterised as good quality habitat with extensive hedgerows and streams lined with mature oak trees. The designated sites listed below are located in between Plucks Gutter and Broad Oak reservoir. The raw water intake pipeline route avoids these designated sites and any ancient woodland.  Stodmarsh SAC (Special Area of Conservation), SPA (Special Protection Area) and Ramsar  Blean Complex SAC  Sturry Pit SSSI  Blean Woods NNR (National Nature Reserve)  East Blean Wood

The West Blean and Thornden Wood SSSIs are located between Broad Oak and Blean. The treated water supply pipeline is routed away from this designated site.

There is a historical land fill site north of Hersden about 3km east of the proposed Broad Oak Reservoir along the raw water intake pipeline route. Shelford Landfill is located about 1.5km southwest of the proposed Broad Oak Reservoir along the treated water pipeline. The pipeline routes avoid crossing historical landfill sites.

There is a large swathe of Grades 1 and 2 Agricultural Land to the East of Broad Oak. In these areas the pipeline routes follow farm boundaries and corridors of hedgerows where possible, to minimise impact on the farming activities during construction and ensure ease of access to the pipelines for future operation and maintenance.

The raw water intake pipeline route passes through large areas of a drinking water groundwater catchment. Nitrate vulnerable zones are present to the west of Broad Oak along with the treated water supply pipeline. Therefore, due consideration shall be taken to minimise movement of particles and hence avoid contamination during construction of the pipeline.

3.5.4.2 Water Courses The pipeline routes are defined to minimise the number of major water course crossings.

The raw water pipeline route crosses a few manmade and natural drains in the Sarre Marshes. The major water courses that the pipeline crosses are:

 The River Wantsum – EA designated river at chainage 1240

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 The Severnscore Dyke – EA designated river at chainage 2620  Island Road Dyke (Stour (Kent) Inland drainage board designated Water Course) at chainage 3060. The treated water supply pipeline crosses Sarre Penn River at chainage 4520.

3.5.4.3 Geology

The bedrock geology along the raw water intake pipeline route is predominantly Thanet Sand Formation and London Clay overlaying Harwich Formation. Thanet Sand Formation is found in the first 4km (Plucks Gutter to Wall End) of the pipeline route. For the remainder of the pipeline route London Clay overlaying Harwich formation is present. The London Clay and Thanet Sand Formations are separated by a narrow strip of Harwich and Lambeth outcrops around Upstreet.

The bedrock between Broad Oak and Blean along the treated water supply pipeline route is London Clay.

According to the published 1 in 50,000 map obtained from the BGS website, the superficial geology along the raw water intake pipeline and treated water supply pipeline routes comprises Tidal Flat deposits, between Plucks Gutter and Wall End, Alluvium deposits along the Sarre Penn banks (Wall End to Chislet Park), and quaternary period clay and silt deposits from Chislet Park to Blean across Broad Oak along the banks of Sarre Penn.

Jacobs is in the process of preparing a geotechnical interpretive report focusing on areas adjacent to the proposed Broad Oak Reservoir. There is also a site investigation survey which was carried out by Norwest Holst in 2008 as part of previous Broad Oak Reservoir studies. The proposed raw water intake pipeline route predominantly follows the route corridor defined in the 2008 outline design, with some realignment around the reservoir. Most of the information gathered by Norwest Holst is therefore relevant however additional data and an interpretive report are required as the project progresses.

No site investigation has been carried out along the proposed treated water supply pipeline route. A detailed site survey and interpretative report shall be carried out as the project progresses to identify any major geological issues that may affect the pipeline route prior to detail design.

3.5.4.4 Existing Infrastructure

The raw water intake pipeline route crosses a railway line at a chainage of 2180. Island Road (A28) runs approximately 500m north of this railway line. The raw water intake pipeline crosses this road at chainage 4120. The pipeline route also crosses Herne Bay Road (A291) at chainage 11,130. The general layout of the area does not allow the pipeline route to avoid crossing these transport links.

In addition the raw water intake pipeline route crosses the following minor roads:  Gore Street (at chainage 220)  Nethergong Hill (at chainage 5,170)  Hoath Road (at chainage 9,080)  Barnet’s Lane (at chainage 11,670)  Mayton Lane (at chainage 11,970)

The treated water supply pipeline route crosses the A290 at chainage 6340 and the following minor roads:  Barnet’s Lane (at chainage 630)  Mayton Lane (at chainage 930)  Giles Lane (at chainage 4,140)  Canterbury Hill (at chainage 4,470)

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These are not considered to be unusual crossings and as such do not result in significant risks to the project.

3.5.4.5 Existing Services

A services search was conducted for the area within the South East Water Land boundary around the proposed Broad Oak Reservoir. The search did not therefore cover the entire pipeline route.

The main services affecting the pipeline routes near the reservoir are BT and UK Power Network (UKPN) overhead lines and cables. Near the reservoir, the raw water intake pipeline will intersect underground BT cables at three points (at chainage 10,860, 11,130 and 11,680), BT overground cables at one point (at chainage 11,980), and UKPN power cables at five points (at chainage 10,850, 11,130, 11,690, 11,840 and 12,330). In addition, the pipeline crosses Southern Water pipelines at chainage 11,160, 11,910 and 11,980, and overhead power lines at chainage 4,520 and 12,500m.

The treated water supply pipeline route crosses UKPN services at three points (at chainage 650m, 810m, and 1,280m), and BT underground (at chainage 640m) and overhead services (at chainage 940m). Additionally, the supply pipeline crosses a Southern Water pipeline at chainage 870m and 980m, and power lines at chainage 1,460 and 2,020m. Near the reservoir, the intake and supply pipelines have been designed to run side by side in the same trench. This minimises the number of separate crossings with existing services.

Further west from the reservoir, near Tyler Hill, the treated water supply pipeline crosses additional services. These comprise a Southern Water line at chainage 4,380, a BT overhead line at chainage 4,220 and 4,450, and a BT underground line and Scotia Gas Network line at chainage 4,460.

The location of the reservoir, and other constraints such as local buildings and infrastructure, means that crossing the above services is unavoidable. Alternative pipeline routes that reduce the number of service crossings would involve large diversions around the buildings in Broad Oak, which would not be economically feasible.

3.5.4.6 Planned Infrastructures and Services

There are no known planned infrastructures and services in the area other than the proposed 400kV overhead power line by National Grid.

There are areas identified as allocated for residential development in Broad Oak and Chislet in the Canterbury City Local Plan. The allocated land is located south of existing housing in Broad Oak and does not impact on the reservoir/RCP corridor, therefore not required to be considered as a constraint or risk.

3.5.5 Brief Description of the pipeline routes

3.5.5.1 Raw Water Intake Pipeline

The proposed raw water intake pipeline route is shown in drawing 502 (Appendix G). The pipeline route nearby Broad Oak Reservoir is shown in Drawing 503 (Appendix G).

The proposed raw water intake pipeline starts from Plucks Gutter river abstraction and crosses Gore Street approximately at chainage 200m then continues through the Sarre Marshes. From there it goes north west to cross the railway line at chainage 2,180. The pipeline route then runs along the north side of the railway line for about 1km before it turns northwest before it crosses the A28 at chainage 4,120. The pipeline then crosses the 132kV overhead power line north of Upstreet. The pipeline route continues north of the power line and crosses Nethergong Hill Road at chainage 5,170, before diverging to the open area north of Chislet Park. Following the southern bank of Sarre Penn, the pipeline crosses Hoath Road north of the junction with Bredlands Lane.

The pipeline continues in a westerly direction along the south side of the Sarre Penn. It avoids Kemberland Wood to the south, and then diverges south to cross Herne Bay Road. From there it continues towards the Broad Oak Reservoir and ends at the outfall into the reservoir.

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3.5.5.2 Treated Water Supply Pipeline

The treated water supply pipeline starts at the proposed water treatment works, and goes south for 270m, before turning west, running alongside the proposed raw water intake pipeline as shown in Drawing 502 (Appendix G). Southwest of the reservoir, the treated water supply pipeline route is constrained by the West Blean and Thornden Woods SSSIs and Shelford Pit (a historical landfill site). The pipeline is therefore routed through a narrow corridor between the SSSI and Shelford Pit. It further avoids Brickhouse woodland to the southeast and follows hedgerows north of Eastingdown and Little Farm. From there it diverges north at chainage 3,960. The pipeline then crosses Canterbury Hill road south of the junction with Calais Hill and Wood Hill roads. Crossing Canterbury Hill Road is constrained by the properties along the road. Therefore, the crossing following the Sarre Penn river is considered to be the preferred crossing. Further site investigation is required to validate the feasibility of this crossing. After crossing Canterbury Hill Road and an abandoned railway track further east of this road, the pipeline route follows the northern bank of Sarre Penn. The pipeline route diverges north towards the Hare & Hounds Inn to cross Blean Hill road. About 400m from the crossing, the pipeline route turns north towards Blean Service Reservoir.

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3.5.6 Pipeline Capacity

The raw water intake pipeline capacity is governed by the hydrology of Stour River and the capacity of the reservoir.

The treated water supply pipeline capacity is dependent on the yield of the reservoir.

The capacity of the reservoir is estimated to be 4,400Ml at top water level of (TWL) 36mAOD. The rate of filling required for such capacity is in range of 100Ml/d. The capacity and the rate of filling of the reservoir including the yield of the reservoir are under review. Subject to further hydrological assessment a diameter of 1000mm for raw water intake pipeline and a diameter of 600mm for the treated water supply pipeline are considered.

The capacities and sizes of both pipelines shall be revised following detail hydrological analysis. Further economic analysis that takes into account capital cost, operational cost and socio-economic cost shall also be carried out to determine the most economical pipe sizes.

3.5.7 Associated Structures In addition to the pipelines described above, the Broad Oak Reservoir scheme also comprises an intake pumping station at Plucks Gutter, an outfall structure at the reservoir, and high-lift pumps to pump treated water from the proposed treatment works to Blean Service Reservoir. The outline design of these supporting structures is outside the scope of the current study.

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4. Outline environmental mitigation and enhancement for the reservoir

4.1 Stakeholder Requirements The approach taken for identifying and addressing key environmental impacts for the reservoir developed from the Water Resource Management Plan (WRMP) 2014 process and the formal consultation from the statutory consultees. The option development for the reservoir took account of the need to avoid direct loss of ancient woodland and SSSI and proposed a smaller reservoir outline based on the 32.5m OD. As part of the consultation process, statutory consultees provided their comments to Defra on the WRMP and the plan’s Strategic Environmental Assessment (SEA) Environmental Report. Natural England’s comments recognised the reservoir option avoided the direct loss of SSSI but highlighted the potential significant indirect impacts related to the scale of landscape change from the reservoir inundation, and stated that:

‘To ameliorate these impacts a significant amount of woodland and semi-natural habitat creation is required. The small reservoir size of the option in WRMP14 allows for the implementation of these significant opportunities to mitigate the impacts of the reservoir. In addition improving the connectivity of the SSSI woodland parcels and that of the surrounding woodland sites offers opportunities for biodiversity enhancement above mitigation.’

The consultation comments also included concerns raised over water quality with a smaller reservoir and emphasised the importance of avoiding loss and fragmentation of the SSSI/ancient woodland if any larger reservoir was considered.

The WRMP consultation comments were taken on board as a starting point to include in the concept design for the reservoir. The key principles for avoiding impacts on the SSSI/ancient woodland and providing the environmental mitigation and enhancement required were set out in the Concept Plan: Landscape, Ecology and Recreation Briefing Note, Jacobs, November 2014. This Concept Plan was discussed with Natural England, SEW and National Grid at a meeting on 18th November 2014.

Comments received from Natural England as part of consultation on the SEW WRMP 14 and in their letter of 11th December 2014 highlighted the importance of the following key points of relevance for the design development and mitigation and enhancement to this study:

 WFD implications for the proposed Sarre Penn diversion Loss and fragmentation of ancient woodland/SSSI from the reservoir and alignment of the Sarre Penn diversion;

 Provision of aquatic biological connectivity and maintenance of fish passage (also related to WFD);

 Avoidance of direct loss and fragmentation on the surrounding ancient woodland and SSSI from reservoir inundation and the Sarre Penn diversion channel;

 Improvement to the connectivity of the SSSI woodland and that of the surrounding woodland sites offering opportunities for biodiversity enhancement above mitigation;

 Provision of appropriate planting along woodland boundaries to complement the character of the existing woodland and to allow species movement; and

 Considering shading and landscape implications of the secondary embankments.

These aspects were also discussed further at a site visit with Environment Agency and Natural England. As a follow up to the site visit Natural England issued a further letter 2 July 2015 highlighting concerns over the larger reservoir size and the size of the secondary embankments identified in the concept design with potential impacts on the adjacent SSSI/ancient woodland. The diversion design developed in through the stage 1a study has reduced the height of the embankments required to around 5m.

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The Natural England letter also notes that for the river diversion the alignment through the narrow strip of woodland is considered potentially acceptable compared to the alternative through the southern block of unit 31 and it is the former route that has been taken forward in this stage 1a study.

The Environment Agency emphasised in discussions on the Sarre Penn, the paramount importance for any diversion design providing an appropriate river gradient and ensuring the functionality of the river as a habitat for spawning brown trout including allowing fish migration up and downstream.

These are early stage comments on concept design development and have been taken into account in the elaboration of the reservoir and Sarre Penn diversion mitigation and enhancement measures described below.

4.2 WFD Compliance

The Environment Agency requires an assessment of the impact of any works/modification to water bodies in the UK under the European Union’s Water Framework Directive (WFD) 2000. The primary aim of the WFD is to improve/maintain the Ecological Status/Potential of all water bodies. Ecological quality comprises a series of biological, physico-chemical and hydromorphological ‘quality elements’. A preliminary WFD compliance assessment was undertaken as part of initial work on the outline design of the proposed Broad Oak reservoir scheme and will be included as an appendix to Geomorphological Report provided in Appendix D in later revisions once this has been reviewed. The preliminary assessment aims to establish the baseline conditions, evaluate potential impacts of the scheme and provide a high level assessment of the potential compliance of the scheme with and without mitigation in place.

The sequence of the WFD assessment is summarised below.  Step 1: Identification of the baseline conditions from desk study and site walkover of the biological, physico-chemical and hydromorphological quality elements.  Step 2: Site specific assessment of the proposed scheme against biological, physico-chemical and hydromorphological quality elements;  Step 3: Review actions to deliver WFD mitigation measures; and,  Step 4: Assessment of proposed options against WFD status objectives and European Union legislation.

The proposed diversion of the Sarre Penn water body would require the river to be perched on the southern edge of the new reservoir. The works would require alteration of the existing channel gradient and planform potentially impacting biological, physico-chemical and hydromorphological quality elements. Although the design might not re-instate a like-for-like replacement of the in channel habitat, there is potential to mimic the fundamental morphological processes that exist in the channel at the current time. However, further detailed assessment would be required to establish compliance of the proposed scheme.

The RBMP mitigation measures assigned to the water body have been assessed against the scheme to establish potential compliance. Based on the information available, none of the assigned mitigation measures are considered to be ‘in place’. The majority of the RBMP mitigation measures are either at low or medium risk of non-compliance due to the scheme, with some further assessment required as part of the scheme to ensure compliance. There are two RBMP mitigation measures that are at high risk of not being complied with. These are measures to:

 Preserve and, where possible, restore historic aquatic habitats; and

 Increase in-channel morphological diversity.

These measures are sensitive to the diversion design but also would need to be considered in terms of the likely sustainability of the river gravel source and river activity and are included as areas requiring further study.

In addition, the scheme provides an opportunity to implement of some of the other RBMP mitigation measures and these would be an improvement on the existing situation in the study area.

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The preliminary WFD compliance assessment has established that there would be potential impacts from the proposed scheme causing a deterioration to the water body status if not mitigated sufficiently.

Specific areas of additional study have been identified to inform the diversion channel design and WFD mitigation requirements further.

More detailed WFD Assessment will need to be completed required for the proposed scheme as the design and mitigation proposals are developed.

A full WFD assessment at detailed design phase would assess the compliance of the scheme, against the following WFD objectives:  Prevent deterioration in the status of water bodies;  Aim to achieve Good ecological and Good surface water chemical status in water bodies by 2015, 2021 or 2027 (depending on feasibility);  For water bodies that are designated as artificial or heavily modified, aim to achieve Good Ecological Potential (GEP) by 2015, 2021 or 2027 (depending on feasibility);  Comply with objectives and standards for protected areas where relevant; and,  Reduce pollution from priority substances and limit discharges, emissions and losses of priority hazardous substances.

4.3 Terrestrial ecological: Potential Impacts

Sarre Penn Riparian Corridor

The Sarre Penn, its tributary stream and the associated riparian corridors are features of ecological value within the Broad Oak Reservoir site. The riparian habitat forms a semi-continuous corridor of mature trees and scrub in the river’s upper section and scattered trees and scrub in the lower section. The channel and riparian habitat forms a linear corridor from west to east throughout the site and is likely to be an important feature for commuting and foraging bats, and potentially valuable for invertebrates, dormice and birds. The value of the river and its riparian habitats is increased given the dominance of large arable fields and fragmented nature of the local landscape. The Sarre Penn river corridor therefore provides important habitat connectivity across the local landscape as well as examples of well-established habitats that are scarce elsewhere on the site.

The proposed site of Broad Oak reservoir is located within close proximity to West Blean and Thornden Woods SSSI. The current outline design could result in impacts to the designated site. It is not within the scope of this document to provide a detailed impact assessment or mitigation proposals for the SSSI; however, a summary of the main potential impacts to the SSSI as a result of the outline design is provided below and will be used to inform an outline mitigation strategy, as detailed in Section 4.8, below:  Potential loss of a small area of ancient woodland/SSSI due to construction of the proposed new river, with potential for fragmentation and modification of habitat including abandonment of the existing Sarre Penn channel within the SSSI;  Potential for occasional flooding of SSSI woodland near the secondary embankment during high flow conditions where these exceed diversion channel capacity resulting in woodland habitat loss or modification;  Potential impacts of shading as a result of secondary embankment construction;  Significant woodland planting immediately adjacent to the SSSI resulting in hybridisation, introduction of disease and invasive species, or domination by unwanted species;  Changes in hydrology affecting habitats within the SSSI as a result of construction and operation of the reservoir;  Fragmentation between woodland blocks caused by removal of hedgerows and mature trees affecting dormice, bats, heath fritillary and other sensitive fauna;

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 Disturbance and pollution during construction of dams, water treatment works and other infrastructure;  Recreational disturbance caused by increased numbers of visitors and dogs as a result of new footpaths and attractions within or close to the designated area.

The proposed realignment of the Sarre Penn would require a construction corridor to allow the earthworks necessary to achieve the design gradient that is required to maintain a functional aquatic habitat and river flow conditions. The corridor width will vary according to the gradient selected but is likely to require the removal of existing hedgerows, trees and scrub, in addition to the low value habitats provided by arable fields and intensively managed orchards. The loss of the higher value habitats would require mitigation in the form of compensation planting, preferably well in advance of vegetation removal and construction works commencing so that compensatory (and enhancement) habitats have an opportunity to mature and establish.

The removal of existing habitats to facilitate the realigned Sarre Penn has the potential to impact protected species such as badgers, dormice, great crested newts, bats, and reptiles, all of which are confirmed as being present within 1km of the site. Before works affecting these habitats could commence, surveys to confirm the presence or likely absence of these protected species would be required where suitable habitat is likely to be affected. If the presence of protected species is confirmed, works would only be able to proceed once an appropriate mitigation strategy had been implemented and the relevant licence had been issued by Natural England, as necessary.

4.4 Aquatic Ecology: Potential Impacts

The key potential impacts in relation to aquatic ecology relate to the reservoir inundation footprint resulting in the loss of the Sarre Penn and tributary and associated in channel and riparian corridor identified as a valuable habitat supporting populations of brown trout, bull head and eel. The river also provides spawning habitat for brown trout.

The extent to which the impacts on direct loss of habitat and up-stream and downstream habitats can be mitigated with a channel diversion depends on how the diversion can be designed to support the target fish species and avoid creating a barrier to fish migration along the river.

The mitigation requirements are discussed further in section 4.8.

4.5 Landscape and Visual: Potential Impacts

Landscape Designations

No national landscape designations would be affected by the proposals.

At the district level the Canterbury Local Plan has kept the former county level landscape designation of the Blean Woods Special Landscape Area as a retained policy, and proposes to rename and maintain this designation as the Blean Woods Area of High Landscape Value (AHLV) in its emerging Local Plan. The examination of the Canterbury Local Plan will start on 13 July 2015 so the AHLV policy could be relevant in the life of the Broad Oak Reservoir project. The designation extends south from the Blean ridge to the northern tributary of the Sarre Penn; and includes Honey Wood, Timber Wood and Great Hall Wood, along with the fields in the Sarre Penn valley between Great Hall Wood and Little Wood.

The Canterbury AHLV extends to the south of Little Hall Wood but is unlikely to be affected by the proposal due to the intervening ridge line that separates it from Broad Oak valley.

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Figure 4-1 Landscape designations in the vicinity of the Broad Oak reservoir site

Landscape character

At the national level the study area lies within National Character Area (NCA) 113: North Kent Plain and at county level it lies within the Blean landscape character area. The Blean is identified as a landscape in good conditional that is moderately sensitive. Guidelines for The Blean are to conserve and reinforce the existing landscape character.

Figure 4-2 Local landscape character areas

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The Draft Canterbury Landscape and Biodiversity Appraisal identifies the following relevant local landscape character areas.

Table 4-1 local landscape character areas Name Condition Sensitivity Guidelines 19. Blean Woodlands Thornden Very good Moderate Conserve and reinforce 25. Broad Oak Valley [directly Good Moderate Conserve and reinforce impacted] 28. Stour Valley Slopes Poor Moderate Restore and improve 29. Stour Valley Slopes: Poor Low Improve Westbere 36. Blean Farmlands Moderate Moderate Conserve and improve 38. Hoath Farmlands Poor Moderate Restore and improve

A significant effect is predicted on landscape character from the change of land use from open countryside to the reservoir. Whether this change is considered to be adverse or beneficial is largely subjective as many people value views of open water as equally as they value views over open countryside.

However adverse effects are predicted to result from engineered structures associated with the reservoir. These include:  Dam and spillway – a large adverse effect on landscape is likely due its size, mass and location. It would be an incongruous, engineered element obstructing views within and along the valley floor.  Secondary embankments – these would give rise to locally significant adverse impacts, although the potential impacts are largely dependent on the final shaping and level of engineering required. Pumping stations associated with the secondary embankments would be an additional engineered feature. Natural slopes that can be tied into the existing contours and the minimal use of hard or engineered features would help to assimilate the secondary embankments into the landscape, along with reed planting to soften the embankment at the edge of the reservoir.  Water treatment works – a large to moderate adverse potential effect on landscape character is predicted from the introduction of built elements within the valley floor, including secondary impacts from fencing, access, possible lighting etc.  Car parking areas and access roads – locally significant adverse effects are predicted. These effects are likely to be moderate to slight depending on the siting and detailed design of these areas.  Existing pylons and overhead cables – the significance of effects would vary depending on the treatment proposed. It is understood that the UKPN overhead line currently running north-south through the study area may be buried underground which would have a beneficial effect on the landscape character. The NG overhead lines to the west are likely to be unaffected having a neutral effect on the landscape character.

The potential landscape character effects from the realigned Sarre Penn are likely to include:  Incongruous landscape feature on side long ground;  Potential impact of engineered structures/incised channel and fish pools;  Potential landscape impact if the characteristics of the existing dynamic system of the Sarre Penn cannot be replicated in the new watercourse i.e. riffles, pools, berms, eroding banks, overhanging trees, etc;  Potential landscape change to the original course;  Potential impact of earthworks and re-grading required to ‘blend’ into existing contours – including loss of vegetation and field pattern; and  Potential effect of loss of vegetation in the vicinity of the Sarre Penn realignment that is key to mitigating adverse impacts of other features, particularly visual impacts.

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Potential visual receptors

As with landscape character the perception of views of the reservoir itself is considered to be largely subjective as to whether the effect is beneficial or adverse. Many of those who experience a view of open water may consider this to be betterment, whereas those who have direct views of engineered or infrastructure elements are likely to view these elements negatively and these views would be assessed as having an adverse effect.

A detailed visual impact assessment would need to be undertaken to determine the magnitude and significance of the proposals: however the initial field study has identified that the following effects are likely.  Residents of properties along the northern edge of Broad Oak village are likely to experience limited views of the reservoir due to the intervening tree cover. Of those views that they are likely to experience these would be generally of open water. The engineered features are likely to be less visible in their view. Views from Mayton Cottages are likely to experience wider views over the reservoir, particularly in the short term; again these views would be predominantly over open water.  Residents of properties in Calcott are likely to experience adverse visual impacts from the engineered structures of the dam, spillway, water treatment works, particularly in the short term before intervening planting has established.  In the short term there would be relatively little impact on views from Tyler Hill, however the view would gradually change over time as new planted woodland establishes in the Sarre Penn valley. Adverse views of the reservoir and associated structures are unlikely.  Residents in the vicinity of Mayton Farm would experience a significant change in their view. There would be views of open water on to the north, east and west; medium to long views towards the dam, secondary embankments and water treatment works; along with potentially more local views of proposed car parking areas. The burial underground of existing UKPN 132kV overhead line, currently supported on lattice pylons (for which a cost allowance was made in the statutory WRMP14 scope for delivery of the reservoir scheme), would be beneficial in the view, particularly if it extended to the pylons on the Broad Oak ridge that are visible to the south.  Views from the Blaxland Farm area to the north would be of open water with potential views of the engineered features in the medium to distant views. Similar to above, the burial of existing overhead cables would be beneficial.  Users of existing public rights of way and proposed footpaths and cycleways would experience a range of views including long distant views to and from the ridgelines to the north and south, along with close up views of the engineering features. These views would vary in magnitude and could be both adverse and beneficial.

4.6 Cultural Heritage: Potential Impacts

Archaeological remains

No Archaeological Remains of high value were identified within the design corridor or in close proximity to river diversion/s. Non-designated cultural heritage assets, including Mesolithic, Bronze Age, Iron Age, Roman and Medieval finds and features are present in close proximity to the design corridor.

Potential adverse impacts on Archaeological Remains are predicted as a result of proposed river diversion/s, including the partial or complete removal of unknown Archaeological Remains that fall within the construction footprint of the river diversion/s, including any compound/set down areas. The potential also exists for adverse impacts on unknown Archaeological Remains which may be of high value. Historic Buildings

No Historic Buildings of high value were identified within the design corridor or in close proximity to the river diversion/s. Five designated Historic Buildings of medium value have been identified in close proximity to proposed river diversion/s. Potential adverse impacts are predicted on two Conservation Areas; Asset 5 (Tyler

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Hill Conservation Area) and Asset 6 (Allcroft Grange Conservation Area) and on three Grade II Listed Buildings Asset 9 (Summer Hill), Asset 10 (124 Sweechgate) and Asset 11 (Royal Oak Public House).

Potential adverse impacts include the partial removal, severance and an impact on the setting of Assets 5 and 6 and a potential adverse impact on the setting of a number of assets 9, 10 and 11 comprising a change in views to, and from, the assets (not taking into account potential planting mitigation).

Historic Landscape

No Historic Landscape types of high value were identified within the design corridor or in close proximity to the river diversion/s. Potential adverse impacts on undesignated Historic Landscape Types may result from the construction and operation of the river diversion/s resulting in partial or complete removal of assets, severance and an impact on setting.

4.7 Indicative Mitigation Requirements

4.7.1 Terrestrial ecology

Woodland planting mitigation and connectivity enhancement

The main impacts associated with the proposed reservoir include the loss, damage or disturbance of sensitive or valuable habitats (including the West Blean and Thornden Woods SSSI), habitat fragmentation, and impacts to legally protected or notable species of fauna. Although the magnitude of specific impacts has not yet been assessed, it is anticipated that mitigation in the form of significant areas of vegetation planting will be necessary in order to address many of the impacts. For example, the anticipated barrier and fragmentation effects caused by the new reservoir would need to be mitigated by providing new woodland, scrub and hedgerow planting around the reservoir to ensure connectivity with existing retained vegetation. Furthermore, the Broad Oak Reservoir scheme brings with it opportunities to significantly enhance the site’s biodiversity value by creating extensive areas of new habitat, such as wetlands, grassland, woodland and hedgerows, and managing any retained agricultural land in a way that maximises its biodiversity potential. This level of enhancement has been identified as a requirement by Natural England as part of mitigating indirect effects,

Sarre Penn diversion Riparian Corridor

The Sarre Penn would be lost as a result of the proposed new reservoir and so it is necessary to recreate the river and its associated riparian habitats along a new alignment on a like-for-like basis to meet WFD requirements. As much of the river is a semi-continuous riparian corridor, flanked by semi-natural woodland, mature trees and scrub, it will be necessary to recreate these habitats within the riparian corridor of the new river alignment. The tree species found along the Sarre Penn include pedunculate oak, alder, field maple, ash, crack willow and grey willow, some of which have been coppiced; a well-established shrub layer comprising hawthorn, hazel, elder and dogwood is also present. It is therefore desirable to include these species in any new landscape or mitigation planting alongside the new river.

4.7.2 Aquatic ecology and fish

Mitigation principles for retaining optimal river habitat features and functioning and to minimise impacts on river diversity are listed below.

Flow maintenance: to be kept as near to current Sarre Penn flows as possible. This will have impacts on habitat – in particular the flushing action of high flows (also geomorphologically channel-forming flows) will act to cleanse gravels keeping them relatively free of silt, which improves the interstitial oxygen concentrations and ensures a good habitat for invertebrates and embryonic fish – such as brown trout.

Channel design which includes similar morphology to the existing channel. This will ensure that current flow diversity may still exist – with refuge areas in inside of bends and slower flowing pools, coupled with fast flowing shallow riffles and mid-channel bars. Adequate depths of water within the new channel will also need to be considered given the new channel dimensions and flow regime.

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Replacement of channel gravels within the newly constructed channel. Gravel size should be researched to match with current channel gravel sizing – taking account of the likely entrainment under the new flow regime. Gravel sizes should match with those deemed suitable for trout spawning – an approximate range of 15mm- 35mm (Kondolf and Wolman, 1993).

Riparian trees / channel shading (or at least partial shading) to be reinstated. This will act to keep summer temperatures at optimum levels for aquatic species and prevent the overgrowth of instream macrophytes which could clog the channel. This is especially pertinent considering the diffuse agricultural input risk (and consequent elevated nutrient levels) which is a current issue. Riparian shading should be as per the current upper reaches of the Sarre Penn, in its semi-continuous nature, and reflect the current species distribution as far as possible.

4.7.3 Fish pass requirements

The natural movement of fish within river systems is critical to the health and maintenance of populations. Artificial obstructions are the principal reason for the loss of biological connectivity globally. Species that make long-distance migrations are more obviously affected by this loss and include Atlantic salmon, sea trout, eels, river lamprey and shad. Other species of fish, such as brown trout, need to move within and between river reaches for breeding, feeding and shelter.

The selected fish passage option at the Broad Oak site should cater for the target species of interest (e.g. trout – spawning beds). However, with the current lack of knowledge on species distribution within the upper Sarre Penn, the fish pass design should consider all species – including coarse fish and eel. Additionally, consideration of invertebrates within the passage solution would represent an ecosystem approach to connectivity/mitigation as theses form an important part of the complex food web within the catchment.

The interaction with the RCP depends on the type of fish pass that is chosen. The following sections present the options currently being considered at this stage of the study. These can be developed during subsequent stages.

Option 1: Bioengineered fish pass – Vertical slot pool pass

This system is commonly used at high head obstructions to allow for fish passage to upstream catchments areas. Of the step-pool passes, the vertical slot pass is probably the most efficient in terms of its potential to provide passage for a wide range of fish species – from salmonids to coarse fish. Depending on its design, the vertical slot pass can also accommodate large changes in upstream water level, provided that downstream water level varies in a similar manner. A bed roughening material placed within the pass may allow for easement of passage for more benthic species such as lamprey and eel.

Figure 4-3 Example of a vertical slot fishway at a dam

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In terms of considerations for the vertical pool pass design, the pool size is determined by the energy dissipation capacity which will determine how fish cope with turbulence caused by hydraulic jumps between pools. This is described further in Appendix A.

As a guideline, power dissipation densities of up to 100-150 Wm-3 would be deemed suitable for trout and coarse fish species, but values at the lower end of this would be better for smaller less powerful fish.

In terms of fish swimming capabilities and progress through the fish pass, they will need suitable flow velocities within the pass in order to be able to progress through the pass. This will be defined by the flow velocities though the pass (this is a function the discharge and pass size, and also the head drop between pools).

As a guide, Table 4-1 below highlights the range of flow velocities which are suitable for coarse and salmonid fish, and the guideline head drops which they should be able to surmount.

Table 4-2 Option 2: Nature-like Fishway

Coarse fish Brown trout Salmon (Atlantic)

Flow velocities (Max) ms-1 1.4 – 2.0 1.7 – 2.4 2.4 – 3.0

Head Drop (Max) m 0.1 – 0.2 0.2 – 0.3 0.3 – 0.45

Option 2: ‘Nature-like’ fishway

Another option for fish passage at large obstructions is the ‘nature-like’ fishway which can take the form of a low-gradient bypass channel around an obstruction, or a step-pool sequence which may be constructed in more space-limited conditions.

The main objective of nature-like fishways is to provide passage for fish; however they also have the advantage of providing passage and habitat for all organisms of all life stages in the ecosystem, including invertebrates.

Additionally, nature-like channels also provide potential for habitat compensation. A well-constructed nature-like fishway could host a diverse fauna of benthic macro-invertebrates as well as macrophytes, fish and in essence imitate an undisturbed ecosystem. If constructed to mimic the properties of an equal sized natural river with a variable substrate, a low gradient and a variable flow regime, this approach may aid mitigation efforts.

Morphological features such as pools, riffles, meanders and channel braids and flood plain areas (wet woodlands) would enhance the overall habitat quality of the solution and be a positive element for biodiversity in the context of the project.

Fishway structure would depend on how much space is available to build the new channel, and on this basis, can vary from a step-pool style configuration with a higher slope to a low-gradient river which attempts to mimic surrounding lowland river types.

Figure 4-2 below gives an overview of an example fishway (step-pool style) built at the Buchenhoffen Dam in Germany.

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Figure 4-4 Nature-like fishway at the Buchenhoffen dam in Germany (Picture source: Gerbler, Piotr Parasiewicz)

In the consideration of channel slope, head drops and channel length required to achieve acceptable flow velocities should be considered. A slope of 1:25 (4%) slope, would be 20m head (dam height) over 500m distance and potentially acceptable though some ‘pools’ with rock ramp effects would form a feature of the design. A slope of 2% would require 1000m of channel length for a dam of 20m head height.

To achieve a more nature-like meandering river, a river gradient of around 2% would be appropriate. This would mimic river morphology with meanders, refuge areas and potentially wetland / flood storage areas integrated into the design. The advantage of this type of solution is that passage for all species would be provided and full connectivity of the upstream and downstream reaches of the Sarre Penn achieved. In addition, this approach may represent a mitigation opportunity by incorporating habitat creation efforts not only within the river but which can extend into riparian corridor and adjacent land also.

The preference for the scheme is to use the nature –like option but the feasibility of the design for this option needs to be investigated further. The two factors influencing the gradient achievable on a nature-like channel are the head drop from the dam location to the downstream channel, and the ground area available to create a channel of sufficient length.

4.7.4 Landscape and visual mitigation principles

The key principles for mitigation are to:  Conserve and reinforce the strategic habitat network and woodland to reflect of the area’s position on the edge of The Blean. Such habitat creation would help to extend and link the significant resource of ancient woodland situated north of Broad Oak valley and the smaller blocks of woodland on the southern side of the valley.  Avoid visually dominant elements within the open landscape, and where this is not possible establish strategically placed screen planting.  Wherever practicable to use ‘soft’ engineering solutions in preference to ‘hard’, including the shaping and re-grading of slopes and river channels to blend into the existing contours and provide slopes with a natural appearance.  Conserve and reinforce the traditional hedgerow and shelterbelt pattern close to Broad Oak settlement. The aim should be as far as possible to maintain or reflect the traditional orchard character around Broad Oak within a framework of strategically placed woodland and/or shelterbelts to intercept undesirable local and long views. This approach will also avoid impression of large blocks of dense woodland close to Broad Oak village.  Develop a planting and management strategy that is aligned with ecology, geomorphology and aquatic ecology, to ultimately create a sustainable landscape that requires minimal intervention to achieve the design objectives.  Consider advanced planting to intercept views from sensitive visual receptors and to promote early habitat restoration. 57 B14000AG/BORStudy/801 - Rev 2 Stage 1a Study

 Explore opportunities for natural regeneration and/or direct seeding to establish new woodlands where this does not limit provision of early establishment of screening vegetation. Natural regeneration could also be part of an advanced planting strategy.  Allow views out over open water/countryside from the existing and proposed footpath and cycle path network. An illustrative example of the mitigation proposals in the river diversion corridor near the dam abutment is provided in Figure B14000AG/BORStudy/605 included in Appendix G

4.8 Summary of Key Impacts and Mitigation Requirements

A summary of the potential ecological and landscape impacts as a result of the Sarre Penn diversion and the anticipated mitigation likely to be required is provided in Table 4-3, below. This table also describes impacts that might arise as a result of the wider reservoir scheme (e.g. impacts to the West Blean and Thornden Woods SSSI as a result of flooding or shading) that might require mitigation within the corridor of land to the south of the proposed reservoir footprint.

Table 4-3 Summary of potential valuable ecological receptors identified during the Phase 1 Habitat Survey, potential impacts as a result of the Broad Oak Reservoir project, and outline recommendations

Ecologic Anticipated impact as a Outline mitigation and/or recommendations for further work al result of Sarre Penn loss (terrestri and diversion al) receptor

West Loss of SSSI and potential  Minimising the footprint of the proposed new watercourse where it passes through Blean fragmentation and SSSI woodland to reduce impacts associated with habitat loss, fragmentation and habitat modification. and modification of habitat due  Provision of linkages (e.g. felled trees anchored into position, ropes etc) across the Thornde to construction of the proposed new watercourse as a short term measure to maintain connectivity for n proposed new river and species such as dormouse. Woods abandonment of the  Retaining and re-using existing seed rich soils to reinstate disturbed areas within the SSSI existing Sarre Penn SSSI. channel.  Timing construction to avoid the most sensitive times of year for notable species and habitats within the SSSI.  Creation of appropriate buffer zones between the works area and sensitive habitats.  Implementation of standard pollution prevention guidelines during construction and operation.  Carrying out new planting with appropriate native species of local provenance to compensate for any losses of SSSI habitat and to ensure connectivity between woodland blocks is maintained and wherever possible enhanced.  Sourcing all planting stock from an appropriate supplier to reduce the risk of introducing non-native species, pathogens or diseased trees.  Enhance or restore areas of unfavourable SSSI within South East Water’s landholding and elsewhere to offset any impacts as a result of the proposed scheme.

Occasional flooding of  Maximise opportunities for the creation of desirable new and complementary habitats, SSSI woodland from high such as willow/alder carr, where habitat modification within the SSSI is unavoidable.  Enhance or restore areas of unfavourable SSSI within South East Water’s flow events resulting in landholding and elsewhere to offset any impacts as a result of the proposed scheme. woodland habitat loss or  Determine design capacity for diversion for high flows (for example would this be for 1 modification. in 10 year events of greater) and design appropriate engineering solutions to prevent excess water entering SSSI.

Potential impacts of  Undertake landscape/shade modelling to assess the areas affected by increased shading as a result of shade and whether this would result in likely significant impacts. Devise an appropriate mitigation strategy, as necessary. secondary embankment  Carrying out new planting with appropriate native species of local provenance to construction. compensate for any losses of SSSI habitat and to ensure connectivity between woodland blocks is maintained and wherever possible enhanced.

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Ecologic Anticipated impact as a Outline mitigation and/or recommendations for further work al result of Sarre Penn loss (terrestri and diversion al) receptor

 Enhance or restore areas of unfavourable SSSI within South East Water’s landholding and elsewhere to offset any impacts as a result of the proposed scheme.  Sourcing all planting stock from an appropriate supplier to reduce the risk of introducing non-native species, pathogens or diseased trees.

Significant woodland  Carrying out new planting with appropriate native species of local provenance that planting immediately have been ‘health checked’. adjacent to the SSSI  Sourcing all planting stock from an appropriate supplier to reduce the risk of resulting in hybridisation, introduction of disease introducing non-native species, pathogens or diseased trees. and invasive species, or  Enhance or restore areas of unfavourable SSSI within South East Water’s domination by unwanted landholding and elsewhere to offset any impacts as a result of the proposed scheme. species.

Changes in hydrology  Undertake hydrological modelling to identify any likely changes that would be affecting habitats within detrimental to the SSSI. Devise an appropriate mitigation strategy, as necessary. the SSSI as a result of  Enhance or restore areas of unfavourable SSSI within South East Water’s construction and operation of the reservoir. landholding and elsewhere to offset any impacts as a result of the proposed scheme.

Fragmentation between  Minimising the footprint of the proposed new watercourse where it passes through woodland blocks caused SSSI woodland to reduce impacts associated with habitat loss, fragmentation and by removal of hedgerows habitat modification. and mature trees affecting dormice, bats, heath  The provision of linkages (e.g. felled trees anchored into position, ropes etc) across fritillary and other sensitive the proposed new watercourse as a short term measure to maintain connectivity for fauna. species such as dormouse.  New woodland and hedgerow planting with appropriate native species of local provenance around the reservoir that re-connects existing woodlands, hedgerows and tree lines.  Creation of appropriate ‘permeable’ habitats such as rough grassland, hay meadows and scrub that would allow the dispersal of many species of fauna.  Enhance or restore areas of unfavourable SSSI within South East Water’s landholding and elsewhere to offset any impacts as a result of the proposed scheme.  Design appropriate footpaths and fencing to reduce disturbance to habitats, especially by dogs,

Disturbance and pollution  Timing construction to avoid the most sensitive times of year for notable species and during construction of habitats within the SSSI. dams, water treatment  Creation of appropriate buffer zones between the works area and sensitive habitats. works and other infrastructure.  Implementation of standard pollution prevention guidelines during construction and operation.  Enhance or restore areas of unfavourable SSSI within South East Water’s landholding and elsewhere to offset any impacts as a result of the proposed scheme.  Advance hedgerow or woodland planting alongside proposed new access roads to buffer any impacts associated with traffic noise, pollution, litter and/or human disturbance.

Recreational disturbance  Enhance or restore areas of unfavourable SSSI within South East Water’s caused by increased landholding and elsewhere to offset any impacts as a result of the proposed scheme. numbers of visitors and  Hedgerow or woodland planting alongside proposed new access roads to buffer any dogs as a result of new footpaths and attractions impacts associated with traffic noise, pollution, litter and/or human disturbance. within or close to the designated area.

Dormice Loss or disturbance of  Undertake surveys of all suitable habitats affected by the scheme to establish the habitats used for breeding, likely impact to the resident dormouse population.  Enhance retained habitats for foraging, breeding and hibernating dormice by infill hibernating and foraging. planting gappy hedges and reconnecting fragmented or isolated woodland blocks. Severance of linear  Create an appropriate landscaping design that mitigates the impacts of severance as habitats used for dispersal a result of the new reservoir; this would involve providing connective woodland, scrub

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Ecologic Anticipated impact as a Outline mitigation and/or recommendations for further work al result of Sarre Penn loss (terrestri and diversion al) receptor

and foraging. and hedgerow habitat around the entire reservoir footprint, and reconnecting existing fragmented habitats. Habitat isolation.  Create new habitats to mitigate for the loss of hedgerows, mature trees and scrub. In order to increase the diversity of plant species and range of foods available to dormice throughout the active season, species from the following list should be considered for infill and/or new planting: o Hawthorn (flowers provide a spring food source); o Hazel (autumn nuts provide valuable food source in advance of hibernation); o Oak (source of insect prey); o Wayfaring tree (flowers in late summer when little else is available); o Yew (fruits are a favoured food source); o Bramble (quick growing, and provides food for a long period, provides good understorey and nest building habitat); o Honeysuckle (source of nesting material and food).  Planting will be managed in order to maximise its value for dormice. This will include periodic removal or coppicing to ensure the canopy does not shade out other plant species.  Mitigate all impacts accordingly under European Protected Species Mitigation licence.

Great Great crested newts might  Undertake Habitat Suitability Index and eDNA surveys of ponds within 500m of all crested be killed or injured during works areas and then presence/absence surveys, as necessary.  Enhance retained habitats for foraging, breeding and hibernating newts. newts works, and their places of  Create new habitats to mitigate for the loss of ponds, hedgerows, mature trees and (GCN) breeding or shelter may be scrub. damaged or destroyed.  Mitigate all impacts accordingly under European Protected Species Mitigation licence. Breeding ponds might  Create an appropriate landscaping design that mitigates the impacts of severance as a result of the new reservoir. become isolated by the fragmentation effect caused by the proposed reservoir.

Bats Loss, modification or  Identify all potential roost features within the development footprint and confirm the disturbance of existing presence or absence of roosts and the species using them by undertaking emergence/re-entry surveys. roosts in buildings or trees  Identify all important commuting and foraging habitats and the species using them by e.g. a known roost at Vale undertaking transect and static monitoring surveys. Farm.  Enhance retained habitats for foraging, roosting and commuting bats, with particular Loss or modification of emphasis towards any notable species of bats recorded on site.  Create new habitats for roosting, commuting and foraging bats to mitigate for important commuting and unavoidable habitat losses e.g. loss of the Sarre Penn. foraging habitats.  Mitigate all impacts accordingly under European Protected Species Mitigation licence.  Create an appropriate landscaping design that mitigates the impacts of severance as a result of the new reservoir.

Reptiles Killing or injuring of  Undertake presence/absence surveys to confirm the species and population size of reptiles during reservoir any reptiles present.  Implement an appropriate mitigation strategy to reduce the risk of killing or injuring construction. reptiles during construction. Loss or severance of  Enhance retained habitats for foraging, breeding and hibernating reptiles. habitats used for foraging,  Create new habitats to mitigate for the loss of suitable reptile habitat. sheltering, basking or  Long-term management should aim to create/maintain a diverse mosaic of rough grassland, scattered scrub and woodland cover. A number of log and brushwood hibernating. piles should be created around the site to enhance sheltering and feeding opportunities.

Badgers Damage or destruction of  Undertake a follow-up badger survey to confirm the presence and status of setts

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Ecologic Anticipated impact as a Outline mitigation and/or recommendations for further work al result of Sarre Penn loss (terrestri and diversion al) receptor setts. within the proposed development footprint.  Undertake a bait marking study to map the likely extent of badger social group Disturbance of badgers within setts. territories to assess significance of habitat loss.  Minimise or avoid impacts to active setts, notably main setts, if possible. Killing or injuring of  Create or enhance habitats suitable for foraging badgers. badgers. Modification or loss of foraging habitat.

Riparian Loss or disturbance of  Undertake riparian mammal surveys of all affected watercourses and ditches mammal habitats used for breeding, considered suitable for these species. s – otter hibernating and foraging.  Enhance existing retained habitats for otters and water voles. and water Severance or loss of  Create new habitats to mitigate for the loss of the Sarre Penn with enhanced habitats vole habitats used for dispersal for water vole and otter. and foraging.  Mitigate all unavoidable impacts under an appropriate licence from Natural England. Killing or injuring of animals during construction.

Other (e.g. brown hare,  Identify habitats affected by the proposals that are suitable for Section 41 and other notable invertebrates, Kent BAP, notable species (especially invertebrates), undertake appropriate surveys and assess species Section 41 and Red Data potential impacts. Book species)  Identify opportunities to create or enhance habitats for Section 41 and Kent BAP Killing, injuring or species. disturbance of animals during construction. Loss, damage or modification of habitat. Habitat severance and fragmentation.

Habitats (e.g. woodland,  Avoid valuable habitats and mature trees wherever possible within the proposed of hedgerows, rivers and development footprint. Principal streams)  Retain existing mature trees, hedgerows and scrub and incorporate into landscaping Importa nce for Habitat loss or and mitigation planting plans. the modification due to  Where impacts to semi-natural habitats (including semi-improved grassland) and conserv construction or operational mature trees are unavoidable, consider habitat enhancements (e.g. hedgerow ation of impacts. planting, species-rich grassland creation, new ponds) of adjacent areas, as biodiver compensation. sity  Seek to remove or control invasive species such as Japanese knotweed.  Undertake detailed surveys of all important habitats affected by the proposals to identify species or areas of high value that should be protected or translocated.  Arboricultural advice should be sought in relation to trees/woodland and tree preservation orders (TPO).

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Table 4-4 Summary of potential effects on landscape character and receptors, potential impacts as a result of the Broad Oak Reservoir project, and outline recommendations

Landscape Anticipated impact as a Outline mitigation and/or recommendations for further work and visual result of Sarre Penn loss receptor and diversion

Incongruous landscape  Careful consideration of slope profiles to create a natural shape, along with the Landscape feature on side long use of planting to soften and integrate the revised channel into the landscape.  Recreate as closely as possible the visual and functional characteristics of the Character ground dynamic system of the Sarre Penn, including riffles, pools, berms, eroding banks, overhanging trees, etc.

Potential impact of  Wherever practicable to use ‘soft’ engineering solutions in preference to ‘hard’, engineered including the shaping and re-grading of slopes and river channels to blend into the existing contours and provide slopes with a natural appearance. structures/incised  Further work required to explore options and identify landscape impacts and channel and fish pools potential mitigation

Potential landscape  The landscape change is likely to be minimal if the existing channel can be kept change to the original wet. The creation of ponds along the existing channel would align and enhance with the ecological objectives. course  Further discussion/design required to establish the landscape effects.

Potential impact of  Allow for additional space for rounding of cutting and embankment slopes to tie earthworks and re- into existing contours. Where existing hedgerows and trees are not impacted relax slopes as much as possible to form a natural profile, however where grading required to hedgerows and shelterbelts are present consider local steepening to retain. As ‘blend’ into existing a general principle it is preferable to avoid engineered slopes including soil contours – including loss retention/strengthening techniques (e.g. soil nailing). of vegetation and field pattern

Potential effect of loss of  Consider advanced planting to intercept views from sensitive visual receptors vegetation in the vicinity and to promote early habitat restoration.  Key views to be identified through the use of long sections, and informed by of the Sarre Penn visual assessment and zone of theoretical visibility. realignment that is key to mitigating adverse impacts of other features

Long distance views  Consider advanced planting to intercept views from sensitive visual receptors. Potential from Calcott and  Key views to be identified through the use of long sections, and informed by visual assessment and zone of theoretical visibility. visual scattered farmsteads to receptors the north of cleared area and new earthworks, particularly during construction and in the short term

Effects on users of  Allow views out over open water/countryside from the existing and proposed existing and proposed footpath and cycle path network, whilst locally screening less attractive engineering and infrastructure elements. public rights of way ,  Detailed design of all elements to consider the ‘human scale’. footpaths and cycleways

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5. Reservoir with the Richborough Connection

5.1 Introduction

The proposed route for the RCP is shown in Appendix G. This drawing shows:

 The pylon route as published for pre application consultation based on route option C - the route passes just to the south of the southern abutment of the dam with one pylon located between the river diversion to the south and the reservoir inundation area to the north side of the diversion corridor. The pylon route crosses the river diversion channel at two locations just south of the dam abutment and to the west;

 Limit of deviation for the pylon route - indicating the current tolerance for the route as shown in pre application consultation. The limit of deviation could allow some variance in the constructed route alignment within this corridor to accommodate detailed design constraints;

 Access for construction and maintenance - the proposed application order limit for construction and access and maintenance access; and

 An indicative tall tree management zone has been taken for this study here as a 30m corridor wide as an area within which there is potential requirement for height restriction for tall growing tree species. This is not a fixed zone - the height tolerance increases with distance from the pylon cables but is considered a reasonable width for this phase of study to look at potential interactions between the RCP and reservoir proposals. (This indicative management zone was based on the 5.3m wide minimum tree safety clearance zone extending beyond a 17.5m pylon lattice, there is also a clearance requirement of 3.1m for falling trees along the pylon route based on NG vegetation clearance guidance); The clearance requirements are to be clarified for clearance to overhead conductors, especially as this varies the potential tree heights depending upon where between pylons and how the ground level has varied, during further stages of the study.

Additional information on clearance for vegetation in cuttings and maintenance access requirements for the pylons with the reservoir scheme in place is being developed in collaboration with NG.

The RCP route, limits of deviation and access routes (construction and maintenance) have been taken from the drawings published as part of the NG pre-application consultation, on the following website: http://www.richboroughconnection.co.uk/maps.aspx.

The potential issues between the RCP route and the future Broad Oak Reservoir are discussed in the sections below.

5.2 Engineering

5.2.1 Reservoir Permanent Works

The proximity of the three pylons (PC8, PC9 and PC10) in the vicinity of the reservoir will impact upon the future construction of the reservoir, especially during the construction of the permanent reservoir works and requirements for permanent access. To develop both projects successfully, the detailed design of the two schemes needs to continue to progress in parallel, especially at the interface locations. The RCP design should take cognisance of the likely envelope required for the reservoir and river diversion as detailed design of these will lag the detailed design of the RCP.

5.2.2 Pipelines

The raw water intake pipeline crosses under this river diversion just before reaching Broad Oak Reservoir, at chainage 12,740. Further pipeline crossings with this river diversion have been avoided, and the pipelines have been offset a minimum of 30m from the southern edge of the river channel. At a later stage consideration can

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be given to the possibility of locating the pipeline within an excavation along the future maintenance access routes. There are potential conflicts in other areas away from the reservoir between the water pipelines and the RCP. This needs further assessment in subsequent stages.

5.2.3 Construction

The route of the pylons will potentially have an effect on the construction activities required for the construction of both the dam and Sarre Penn river diversion. The area to south of the dam and along the river diversion will be in a large area of earth works encompassing:  Excavation of Sarre Penn diversion  Foundation preparations for the dam  Construction of the dam  Construction of access bridge to the dam crest  Construction of the fish pass  Construction of the water treatment works  Laying of the pipelines.  Access routes for construction of river diversion and reservoir

Constructing these items with the pylons and overhead conductors in place will clearly be a risk. This could be mitigated, for some aspects of the work, in part by completing some of the construction during or before construction of the pylons. However bringing some items of the construction forward does then limit these from being changed through detailed design of the dam and should be avoided where reasonably practicable. Additionally the reservoir and river diversion detailed design would be needed and planning permission sought for the advance works which is unlikely to fit into the timescale of the RCP development. Further to this, large excavations out of sequence are impractical as there is no structure which could make use of the arisings until the dams are constructed, which again would require design and planning permission.

A possible mitigation would be to use smaller construction plant when working adjacent to the pylons and overhead conductors, and using a system of goal posts. This will have an implication on cost and programme for the construction of the dam.

Additionally significant lifting plant would be required, especially for the construction of the access bridge over the diverted river to the dam crest. Although lifting plant may not be required for the construction of the dam itself it will be required for the construction of the structural components including the water treatment works, the draw-off works and possibly the fish pass and the spillway, and lifting the sections of pipeline for the raw and treated water. It may be possible to work around this with careful planning and choice of equipment. This mitigation would be difficult to implement for the bridge lift under the RCP route where the bridge would likely be constructed from pre-tensioned or steel sections. The pylons and overhead conductors in the location of the bridge could cause a significant risk to construction safety and need to be carefully looked at to minimise the impact on the construction of the access bridge to the crest of the dam. This is considered a key risk and further work is required to review the access plan for the reservoir and dam, refer to risk table in section 6.3. Relocation of the access track, such that it crossed the river further to the west, and passing the access track between the reservoir and the diverted Sarre Penn, would result in the river diversion moving further south. This would result in larger excavation for the river, and more land being required for the river corridor. Additionally the pylon on the northern side of the diverted Sarre Penn is essentially on an island, with the reservoir to the north and west, the river to the south and the dam to the east. Therefore any maintenance access required to this pylon once the reservoir is constructed will need to be routed to minimise the impact of having to gain access to this pylon during construction and operation of the future reservoir.

The area of the access bridge should be further investigated during the later stages of this project, to ensure it is compatible with the RCP pylon alignment.

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5.2.4 Reservoir Top Water Level

The final location of the right abutment of the dam, and the Sarre Penn diversion will depend on the final agreed top water level for reservoir. The water level has been taken at 36m AOD for this study, giving a dam crest of approximately 38m AOD. The route of the Sarre Penn diversion has been determined such that there is sufficient space between the river and the dam to construct the dam foundations and such that there is no detriment to dam safety from the adjacent river. Although 36m AOD has been taken as the top water level for this study, if the reservoir level were to be changed at a later date, it could be found that the location of the pylons then encroach on the dam if the water level were raised. Alternatively if a lower water level were to be agreed then the river diversion would move further to the north (to follow the contours), which could clash with the location of the pylon proposed to be located to the north of the river diversion. There therefore remains a significant risk to the delivery of the reservoir scheme due to the pylon to the north of the river diversion constraining the solution to the detriment of being able to successfully deliver the reservoir scheme.

It is difficult to mitigate for this as the top water level has not yet been fully agreed. If the pylons were to pass sufficiently to the south of the river diversion then it would be less likely that a change to the top water level would cause a potential issue.

The points below describe the engineering and constraints for each of the points above. The route of the RCP pylons and the impact of these on the design are discussed in Section 4 of this report. However the main constraint for the pylon locations is where the river passes the abutment of the dam.

Key risks and possible constraints are:  Pylon being proposed north of the river diversion on the relatively flat area of natural ground upstream of the right dam abutment. Location of this pylon would limit the course of the river during detailed design.  Top water level of the reservoir, the location of the river diversion will depend on the top water level of the reservoir. This could result in additional cut being made into the valley where it might otherwise be avoided. The risks here, and possible mitigations, are presented in more detail in Section 6.

5.3 Environmental Mitigation

5.3.1 Sarre Penn diversion corridor A key issue with regard to the impact of the RCP scheme on the river restoration efforts would be towards the lower end of the new diverted channel reach, where the channel corridor is bounded to the south by the RCP pylons which are nearest the dam structure, and the reservoir to the north. This may pose a challenge to river restoration measures if a full corridor of riparian planting and channel features are to be created within the restored Sarre Penn reaches.

The presence of pylons and overhead conductors would restrict the planting of tall trees within an approximately 30m wide indicative management corridor centred on the published route alignment (calculated based on a 5.3m wide minimum tree safety clearance zone extending beyond a 17.5m wide lattice pylon (National Grid, 2015). At locations where the RCP route is located within 30m of the proposed Sarre Penn diversion, a continuous belt of tall trees alongside the river could not be achieved. Furthermore, at one location to the immediate west of Barnet’s Lane where the conductors (wires) would potentially over-sail the Sarre Penn diversion, the tree pylon corridor management zone would encroach into the reservoir’s footprint – this would mean that it would not be possible to achieve a continuous belt of tall trees along the reservoir’s bank. Appendix G shows the anticipated tall tree management zone.

5.3.2 Woodland connectivity in the diversion corridor

Despite the likely encroachment of a tall tree management zone into the Sarre Penn corridor and proposed woodland planting areas, it would still be possible to achieve appropriate species planting to mitigate potential impacts to protected species such as dormice, great crested newts, and bats. The provision of hedgerows (especially those that can be managed so that they form a ‘leggy’ structure), scrub, coppiced or pollarded tall

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trees, and low growing trees (such as field maple, grey willow, hazel and holly) would be adequate to mitigate anticipated impacts to protected species as a result of habitat loss, severance and fragmentation, especially as this ‘restricted’ planting would only be confined to localised areas towards the eastern extent of the river diversion. As such, provided that some form of woody habitat connectivity comprising appropriate species, could in theory be maintained within the RCP route corridor, the presence of overhead conductors and pylons would not likely represent a significant constraint to any anticipated protected species mitigation.

However some specific issues are identified in the species planting list and the management of the tall tree management zone. It is not clear at this stage the extent of disturbance that regular height management would cause along this corridor and further discussion is required on the scope for sensitive management e.g. potential frequency and rotation of and permitted maximum height of vegetation within the corridor. The potential to allow higher growing tree species within the deeper areas of cutting also needs to be explored further to the pylon route impact on the woodland connectivity. In addition to the permeability of the corridor to protected species the effect of corridor species mix and management regime on the invertebrate assemblages associated needs to be considered.

Any requirement for future access to the pylon located between the river diversion and the reservoir needs to be looked at further to clearly understand if there is any further fragmentation of the habitat at this point as the reservoir design evolves.

5.3.3 Riparian Corridor for the Sarre Penn diversion

The realigned Sarre Penn would need to replicate the existing riparian habitats on a like-for-like basis. The results of a River Corridor Survey (LDA, 2006) and a Phase 1 Habitat Survey (Jacobs, 2015) show that the upper reaches of the Sarre Penn support mature high canopy trees and broadleaved woodland on at least one bank, with the lower reaches comprising scattered trees and scrub. The landscaping concept plan currently shows a wooded corridor located along the entire length of the diverted river. Localised breaks in the tree line or areas of low canopy trees imposed by a RCP tall tree management zone could be accommodated to some extent, assuming requirements were limited to like-for-like habitat replacement, given some of the existing riparian tree cover is already ‘gappy’ in places, especially the lower reaches - this would also coincide with the area where cables would potentially be located. However this would still need to be kept to localised breaks in tall tree cover and continuity of the corridor maintained with the effective shading at least on the southern bank in order to achieve the desired aquatic habitat conditions. The extent of NG tolerance to taller tree growth within the cutting especially along the southern bank needs to be explored further.

Clarity on how ‘like for like’ replacement will be interpreted requires detailed discussion with the Environment Agency including how this principle would be applied for WFD component elements and the extent that betterment may be required in some areas to compensate where like for like elements cannot be fully achieved. The key overall test is understood to be that the habitat functionality of the river is maintained to the extent that there is no status deterioration or hindrance to RBMP and WFD waterbody status objectives being met.

5.3.4 Woodland connectivity for the scheme

It is a requirement for the Broad Oak Reservoir project to significantly enhance the biodiversity value of SEW’s landholding by replacing habitats of low ecological value (arable fields and orchards) with high value habitats that contribute towards national and local Biodiversity Action Plans and satisfy SEW’s duties under the Water Industry Act’s Recreation Code of Practice on Conservation, Access and Section 40 of the Natural Environment and Rural Communities Act 2006. The project’s concept plan outlines details of a belt of continuous woodland planting along the southern and eastern sides of the reservoir to connect Little Hall Wood (to the west) and Farthings Wood (to the north east). The presence of a tall tree management zone would potentially prevent the creation of continuous high canopy woodland at the south-eastern corner of the reservoir but as detailed above, adequate connectivity could potentially be achieved by managing the height of tall growing trees, using low growing trees and ‘permeable’ habitats such as rough grassland, scattered scrub, tall herb communities and low intensity orchards but this is again dependent on the level of maintenance and regular disturbance required within this corridor and the potential to adapt this to minimise impacts on target species.

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The western RCP route crossing point management zone is likely to be easier to accommodate than the area south of the dam abutment where the RCP route passes parallel to the river corridor and would require restrictions to tall tree growth at a pinch point in the design. Potential mitigation planting in this area shown in see Figure 5-1 aims to minimise this effect but it remains the narrowest point in the corridor and the acceptability of the proposals for riparian and woodland connectivity need to be discussed further with Natural England. A summary of the landscape impacts of the RCP pylons with the reservoir and outline mitigation requirements are set out in the table 5-1 below.

Table 5-1. Summary of potential effects on landscape and visual receptors related to the reservoir proposals in the area of interaction with the Richborough Connection Project

Landscape and Potential impact of National Outline mitigation and/or recommendations for further work visual receptor Grid RCP pylons on proposed reservoir scheme

Landscape Loss of existing vegetation Vary the heights of planting, through species selection and management, on the Character and limitation on planting edge of the tall tree management zone to provide diversity and a graded edge to opportunities: soften its appearance and potentially intercepting some views.

NG proposal assumes a linear Consider opportunities for advanced planting to intercept local and long views. tall tree management zone of 30m which would pass The extent linear views are opened up along the corridor and limitations on through existing tree belts and opportunities to create a setting /backdrop for the reservoir and Sarre Penn proposal orchards, need to be looked into further with more in depth understanding for NG proposals and extent of tree removal required.

Develop a planting and management strategy to establish how proposed mitigation can be delivered, including identifying responsibilities for future maintenance.

Cumulative impact of During earlier reservoir studies it appears that consideration was given to the UK realigned existing pylons and Power Networks (UKPN) (formerly EDF) pylons that run north to south through the NG RCP pylons – particularly reservoir site would be buried underground, reducing the impact over the current on Broad Oak ridge situation.

Confirmation is required of this proposal and its extent. If the UKPN pylons remain on the Broad Oak ridge to west of the village there is a potential cumulative visual impact on receptors to the north.

Plant ‘high canopy’ woodland and/or strategically placed woodland/shelter belts (such as along the SEW southern ownership boundary) on the slopes above the pylons to provide a backdrop to soften the impact on the skyline.

Create a mosaic of remnant orchards/grasslands within the woodland/ shelter belts to maintain the traditional character immediately around Broad Oak.

Consider advanced planting to intercept local and long views proposed pylons.

Level change around eastern Additional work required to consider the space that maybe required for re-grading to pylon create the Sarre Penn realignment/fish pools and the impact it may have on the pylon location.

Access to pylons Additional work required to understand and consider the relationship of maintenance access to the pylons with other elements, in particular the pylon to the north of the Sarre Penn realignment and its relationship with the proposed cycleway. There is

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Landscape and Potential impact of National Outline mitigation and/or recommendations for further work visual receptor Grid RCP pylons on proposed reservoir scheme

potential for this to be a shared surface but would be dependent on the frequency and scale of use by NG including size of vehicles, turning circles, working space etc.

If a separate access is required then the route and mitigation needs consideration. The objective should be to keep as low key and unobtrusive as practicable, and to be located so that it does not limit or distract from essential mitigation or desirable enhancements to the reservoir proposal. .

Potential visual Loss of existing vegetation Consider advanced planting to intercept views proposed pylons. receptors: and/or potential screen planting due to pylon Manage existing vegetation to provide screening/softening of views of the pylons Residents and construction, access and the and overhead cables footpath users at tall tree exclusion zone Broad Oak requirements, potentially Create a mosaic of remnant orchards/grasslands within the woodland/ shelter belts opening up views of the pylons to maintain the traditional character immediately around Broad Oak. and reservoir.

Residents and Impact on long views including Consider advanced planting to intercept local and long views proposed pylons. footpath users at cumulative adverse impacts Calcott, and from engineered features Plant ‘high canopy’ woodland and/or strategically placed woodland/shelter belts Mayton and associated with the reservoir (such as along the SEW southern ownership boundary) on the slopes above the Blaxland Farm and proposed and existing pylons to provide a backdrop to soften the impact on the skyline. areas. pylons on the Broad Oak ridge.

5.3.5 Planting Mitigation Strategy

Consideration of National Grid species list In the Richborough Connection Project Proposed South East Water Reservoir Route Options Appraisal (NG 7/11/2014) National Grid has offered a number of species that will ‘meet safety clearance requirements, providing they receive appropriate maintenance every 2 to 3 years.’ The NG list largely comprises species that would naturally form a woodland or riparian shrub layer, such as wayfaring tree (Viburnum lantana) and holly (Ilex aquifolium). The list also includes some small to medium sized tree species including field maple (Acer campestre), crab apple (Malus sylvestris) and hazel (Corylus avellana). However maintenance to meet safety requirements, such as coppicing, would prevent them from achieving ‘standard’ high canopy form.

Shrub layer species that are present in the adjacent woodlands but are not on the NG list include wild service tree (Sorbus torminalis), midland hawthorn, (Crataegus laevigata) and butchers broom (Ruscus aculeatus).

Desirable high forest tree species found locally but not on the NG list include sessile oak, beech, hornbeam, ash and, common to watercourse and wet areas, crack willow, alder.

Tree species that have traditionally been coppiced include sweet chestnut and birch, field maple and hazel; these species are often managed either in compartments or as coppice with standards.

English Nature’s Planting and Management Strategy The following planting and management principles have been extracted from the English Nature Document, ‘A statement of English Nature’s views about the management of West Blean and Thornden Woods SSSI’ (EN 02/08/05). The same principles can be applied to the proposed reservoir woodland and riparian planting.

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Planting and Management Principles (For existing and proposed woodlands):  A diverse woodland structure with open space, a dense understorey and a more mature overstorey is important;  A range of ages and species within and between stands is desirable;  Some dead and decaying wood, such as fallen logs, can provide desirable habitats for fungi and invertebrates;  Both permanent and temporary open spaces, of sufficient size to ensure sunny conditions prevail for most of the day, benefit groups of invertebrates such as butterflies;  Felling thinning or coppicing may be used to create or maintain variations in structure, spread throughout the wood to promote diversity;  Dormice are often associated with traditional coppice with standards, which provide a good range of foods in small areas;  Dormice benefit from a high species diversity of woody plants, within a well-connected woodland structure, allowing arboreal movement between trees and shrubs;  Dormice are reluctant to cross open ground, so clear areas should be small;  Natural regeneration from stump or seed regrowth is preferred to planting to help maintain the local pattern of species and inherent genetic character of the site, and,  Where planting is required, select species to maintain the local pattern whenever possible propagated from the local gene pool (added).

Specific Targets (Relevant to NG proposals and realignment of Sarre Penn watercourse)  To enhance and reconnect woodland to create an extensive block of habitat, particularly through the maintenance and restoration of coppice management  To create a riparian corridor alongside the diverted Sarre Pen watercourse that is comparable to and wherever possible better than the existing habitat, particularly though the provision of appropriate riparian planting to maintain the local pattern and reconnect the watercourse with upstream and downstream reaches

Application of planting and management principles to proposed National Grid pylon corridor

Consistencies  The NG species list is largely aligned with shrub species that would be selected for the reservoir scheme with some amendments required. The planting and management principles noted above could largely be applied in principle to the pylon corridor but would require specific application of a sensitive management plan for the pylon corridor within the reservoir taking on board the principles outlined. Inconsistencies  The NG species list does not include all shrub species that might be required for the scheme and some that would not be suitable.  The NG species list does not include any high canopy trees  NG safety clearance requirements require that maintenance be carried out at a frequency that does not align with traditional coppice management or need to minimise disturbance to meet species connectivity requirements  Sensitive management will be required to maintain a well-connected woodland structure at all times

Summary of key environmental mitigation issues

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Key issues of potential conflict or interaction with the RCP pylon route are summarised in drawing 1008 in Appendix G. These include:  The south west pylon location which could conflict with the road diversion for the Sarre Penn corridor construction – consideration needs to be given to accommodating the road diversion required.  Limitations on tree height within the (approximately) 30 m pylon route corridor leading to loss of high canopy trees along the Sarre Penn riparian corridor and within the associated woodland planting belts providing east- west woodland connectivity.  The pylon between the reservoir and the Sarre Penn – with associated access for future maintenance (requirements to be confirmed dependent on the design of the reservoir and river diversion) potentially adding to land take here.  Collection of engineering structures at the south end of the dam abutment where the RCP route oversails an access bridge over the river diversion; this bridge is part of the access to the dam crest and the cycleway and also links with the Sarre Penn corridor bridleway/access. Along with the limitations to planting under the RCP route, there are potential additional visual and habitat continuity issues.  Pylon south of the Water Treatment Works - the design for the fishpass has to be developed further, but the options discussed are likely to require additional space to provide the river gradient and pools and associated habitat involved and the potential for interaction between the fish pass, RCP pylons and the water treatment works and SEW mitigation planting requirements to provide screening from key cross valley views from the north.  Key existing view-points are highlighted at Blaxland Farm and Calcott. Future new key view-points to consider with the reservoir will be from the visitors centre. These views could be affected by the RCP.

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6. Conclusions and Recommendations

6.1 Introduction

This report covers the work that has been completed to the end of Stage 1a. The work has identified a number of areas of risk and uncertainty for the development of the reservoir with the RCP.

The stage 1a findings were presented to NG and SEW for discussion on the 25th June 2015 and comments from this meeting and their review of the draft report have incorporated into this report as appropriate. The study findings were updated and presented in a meeting on 13th July 2015 with Environment Agency and Natural England also attended by NG, SEW and Jacobs.

Comments were issued to Jacobs by NG on revision 1 of this report on 20th Sep 2015 and SEW provided their comments to these on19th October 2015. Jacobs circulated their responses to the NG and SEW comments and a draft of proposed revision 2 of this report to NG and SEW on 21st January 2016. Jacobs met with NG and SEW on 14th March 2016 to review comments, responses and proposed draft report and seek an agreed position to issue a revised final issue as revision 2.

The key findings are summarised below with a risk table identifying the level of risk in terms of the RCP published route affecting the feasibility of delivering the reservoir. The relevant mitigation measures required to reduce risk are identified and further summarised interns of the recommendations for the stage 1b or stage 2 study.

6.2 Key Findings

Environmental mitigation requirements

1. WFD/aquatic ecology requirements - the Sarre Penn channel diversion has potential to provide a ‘like for like’ replacement for the loss of the Sarre Penn section to meet WFD water body status no deterioration and RBMP objectives but requires further study to confirm the requirements and how these can be met through design within the river corridor area identified. • The diversion channel needs to provide functional habitat capable of supporting spawning brown trout with the diversion flows keeping gravels clean and the channel replicating the diversity of river habitat in the existing Sarre Penn channel; • The range of average gradients which could provide a basis for creating the habitat required are identified but the gradient will have a significant effect on the depth of the cutting and size of the diversion corridor required; • A nature–like fish pass can potentially allow passage for the range of fish and aquatic species required although the length of channel required depends on the head drop and therefore the channel diversion design and location and this has implications on the footprint for the fish-pass and the land required east of the Dam abutment; and • Riparian vegetation along the river diversion is an important feature for the aquatic habitat especially in terms of the shading and cooling effect and as a wood debris source. The Sarre Penn is also currently an important landscape feature providing habitat connectivity and the riparian corridor for the diversion should be part of habitat connectivity enhancement required for the reservoir scheme as well as being needed to fulfil WFD compliance requirements. 2. Diversion Route alignment - with respect to concerns over SSSI impacts and effect of the secondary embankment with potential for shading, root zone damage, micro climate change and landscape impacts: • The channel diversion can pass through a narrow strip of woodland and across the secondary embankment with the loss of canopy connectivity minimised. In the long term the north south woodland connectivity can benefit from substantial woodland planting in this area; • The diversion has been designed to achieve the gradient range for the river channel with a secondary embankment lowered to around 5m; and 71 B14000AG/BORStudy/801 - Rev 2 Stage 1a Study

• Embankment shading is likely to be minimal due to its location north of woodland edge and this can be assessed further along with the design of the embankment footprint to avoid impacts on the adjacent woodland. 3. Size of Reservoir - the stage 1a study focussed on the larger reservoir size with a top level of 36m OD but the reservoir size could range from a 32.5m to 36m OD top level with the following implications • The River diversion requires a secondary embankment for both the smaller and larger reservoir size also to achieve a diversion gradient within a range likely to be acceptable; • Water quality and feasibility aspects likely to favour a larger reservoir- within the 32.5m-36m OD top level range; • The size of the reservoir can affect the location of the river corridor. However the size the reservoir will be at the detailed design and approval stages cannot be determined at this stage, as it will be influenced by the need to avoid impacts on the SSSI/ancient woodland, the acceptability of the river channel design to the regulators and also the feasibility of the overall scheme taking into account construction cost and water quality issues. 4. Woodland connectivity - the reservoir project is required to provide connectivity and habitat enhancement to mitigate for indirect impacts and landscape scale changes. • Connectivity enhancement potential exists east-west along part of southern bank of river diversion and south of the channel corridor; • Where possible advance natural regeneration /appropriate woodland planting in line with the principles from the SSSI management strategy and including approaches to support dormouse, typical bird and invertebrate assemblages, ground flora , tall tree canopy and encouraging structural diversity should be applied; and • There is a narrow pinch point in the corridor with access structures /bridge south of Dam abutment • Broad Oak village edge - the strategy identifies the need to keep a traditional local landscape character here with a mosaic of woodland edge/relic orchards and shelter belts.

Interaction between the RCP and reservoir

The key interactions from the RCP identified in the stage 1a study essentially arise from the published RCP route being located within the corridor for the river diversion and its proximity to the dam abutment and reservoir top level and fish pass structures as listed below:

• The location of one pylon between the diversion and the reservoir top level close to the dam and access points and within the river diversion corridor is therefore vulnerable to diversion design and reservoir size changes • A length of river diversion route located underneath the RCP route • Fish pass design potentially conflicting with the pylon east of the dam abutment • Constraints to construction of the reservoir • Potential conflict with the southern access to the Dam crest and bridge across the diversion • Habitat enhancement and landscape objectives for the reservoir project may be limited by restrictions to planting and vegetation height management within a corridor around the pylon route. • Impacts on views across the reservoir from the north and east

There is considerable uncertainty over how the detailed design for the reservoir structure will develop in the future and how the range of issues such as regulator acceptability and compliance and feasibility considerations and public consultation views will all balance out. The main concern at this stage is to determine if the deliverability of the reservoir is compromised by the RCP route. The risks from these interactions and potential areas for further study aiming to reduce this risk are summarised below.

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6.3 Risks and Mitigation

The following table highlights the main risks for the reservoir scheme being delivered with the RCP and the potential design mitigation measures to quantify or reduce the risks identified through the stage 1b study.

The risks are those identified as potentially significant within the study work and are tabulated on the risk table. The risks are; - where there is a risk to deliverability and maintainability of either scheme, - where there remains uncertainty in the base data and/or preliminary design and this impacts upon evaluation of the deliverability and maintainability.

The Scope of Works identified for the Stage 1b study is to attain a quantitative or more informed evaluation of the risks. The justification is given for taking these forward.

Risk Stage 1b Tasks to Evaluate Justification for taking and Quantify the Risks forward to study stage 1b. Identified

Re-calibrate the equipment Information required as basis 1. River flow information - Uncertainty installed at the gauging for geomorphological design regarding river flow data (reference section station and re-calculate the and watercourse analysis. 2.9.4.3). Incomplete river flow data for existing historic flows Sarre Penn and high and low flow data that has been received would appear to be unreliable. (reference section 3.2.7)

2. Geotechnical Information - Information on Ground investigation has Conservative assumptions ground conditions is incomplete (reference been ongoing during this can be made, however the section 3.2.7). Ground condition information to stage of the study. More slopes of the river diversion ensure that the river diversion is in clay (or if it information is now available excavation are a large needs lining), and for the design of stable slopes and further refinement can variable in the width of the for the river diversion and dams. be undertaken during river corridor. subsequent stages 3.Topographical Data Further topographical Variance will have an effect The topographical data used, except for the survey is not anticipated on locations of reservoir Sarre Penn channel, were supplied to Jacobs during this study. Stage 1b components and RCP. from an unknown source, and has not been study to verify the datasets Need to quantify level of checked or verified. The location of the dam, and quantify any variance. impact. extent of the reservoir, and location of the diverted Sarre Penn have been based on this contour data. (reference section 3.2.7) 4. Permanent Access – (reference section 3.4). Permanent access to be Southern access route Access is currently anticipated to both North and investigated further during interacts with the RCP, need South extent of the dam, the access to the south stage 1b of the study to to quantify level of impact. requires a bridge over the diverted river which provide more detail on the conflicts with the conductors and pylons, and required solution and forms a construction and operational risk quantify the interaction between the schemes.

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5. Construction risks including construction Construction access Construction access access to river diversion/reservoir (reference requirements for reservoir to interacts with the RCP, need section Section 5.2.3) – mitigate with alternative be investigated during to quantify the level of routes subsequent stages of this impact. project 6. Reservoir top water level. The reservoir top Investigate the reservoir Position of river diversion level has not been agreed. This stage of the boundaries, dam structures corridor and associated fish study has assumed a high top water level, this and course of the river pass varies with reservoir however may be decreased. Decreasing this will diversion for lower water size. Need to quantify the allow the river diversion to move further to the levels to quantify the level of impact across the North. Alternatively a rise to the level would interaction between range of sizes. mean moving the diversion further to the South. maximum and minimum Note Natural England have clarified their likely reservoir sizes. preference for the smaller reservoir size and the reservoir sizing will need to be investigated fully to determine balance of feasibility and impacts 7. Channel design/location - Agreeing a Investigate the existing river Gradient of river diversion channel gradient – setting a fixity on river gravel sustainability to affects the size and extent of diversion design – but risk to detailed design evaluate river the excavated corridor. Addressing peak flow capacity and characteristics to be met Need to quantify the level of geomorphological aspects of Sarre Penn flow with diverted water course impact. and gravel sustainability will influence design and thus seek agreement in criteria Diversion channel gradient would actually be principal to required variable so a suitable limit of deviation may be gradient. This would required confirm the extent of the river diversion corridor and

quantify the interaction. 8. Fish pass type and route - potential for Develop the stage 1a Design of the fish pass greater footprint and interaction with the Pylon Option 2 fish pass design affects the size and extent of east of the dam. including seeking the excavated corridor. agreement in principal with Need to quantify the level of the EA. This would confirm impact the extent of the fish pass corridor and quantify the interaction. 9. Planting scheme - planting for the future, Liaison with NG Jacobs and Need to develop planting coordination of schemes planting and SEW over planting plans that take cognisence of maintenance agreement proposals, coordination and the RCP to identify the level management similar to of impact the RCP places approaches within SSSIs upon achieving an with aim of producing plans acceptable planting scheme acceptable to Natural for the reservoir. England, 10. CDM - applicable to scheme design – need To develop structured Need to quantify the level of to appoint Principal Designer and have hazard identification for impact and seek elimination structured review of hazard of pylons during reservoir scheme in areas or mitigation of hazards. reservoir scheme construction. and operation of interaction and engage in Would naturally in design want to eliminate the CDM liaison for Reservoir hazard by separating RCP and diversion and RCP. corridor.

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11. Pipeline routes – conflict with RCP Pipelines seen as low to Not applicable. elsewhere en-route medium risk through interactions. No further work proposed in stage 1b study. 12. Secondary embankment and flood risk to Model flood events and Needed to support river SSSI - depends on channel design and channel capacity to diversion design to quantify catchment and flood event characteristics - determine extent and the level of impact. reservoir scheme design needs to ensure that frequency of flooding likely inundation of SSSI can be avoided or reduced to to determine potential low probability events- effects and regulators views on acceptable approach- can assist in reducing uncertainty on river channel design.

13. Statutory Regulators - comfort of scheme Maintain ongoing discussion To keep regulators informed and agreements in principle with Natural England and and on-board with design Environment Agency and concept and support build in feedback into certainty of design. Note design and mitigation that unlikely to achieve development agreements leaving uncertainty for future 14 - Contours used – not validated data Obtain validated data – e.g. Variance will have an effect LIDAR to verify the datasets on locations of reservoir used and quantify any components and RCP. variance. Need to quantify level of impact. Additional studies to ensure To improve certainty over 15. Reservoir planning process - may require compliance and regulator design concept being material changes to current concept design – and other stakeholders acceptable to stakeholders. difficulty in future proofing and adding to views are taken into uncertainty over acceptability of RCP within river account at this stage to corridor area. reduce likelihood of unforeseen changes. For SEW/NG to identify 16. Statement of Common Ground - Long term points of agreement and legal Standing of agreements made in Statement disagreement using Stage of Common Ground 1a and following reports for

basis of position taken as appropriate.

The Study Stage 1b scope of work has been defined in a draft Terms of Reference which is to be agreed by SEW and NG and issued to the Environment Agency and Natural England for comment.

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Appendix A. Aquatic Ecology Walkover Report

Report Title; Aquatic Ecology Walkover Report

Report Number; B14000AG-BORStudy-201

Revision; 1

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Appendix B. Extended Phase 1 Habitat Survey Report

Report Title; Extended Phase 1 Habitat Survey report

Report Number; B14000AG-BORStudy-204

Revision; 1

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Appendix C. Hydrological Study

Report Title; Stage 1a – HYSIM Modelling Study

Report Number; B14000AG-BORStudy-302

Revision; 0

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Appendix D. Geomorphological Study

Report Title; Geomorphological Report

Report Number; B14000AG-BORStudy-1012

Revision; 1

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Appendix E. Environmental Constraints Report – Cultural Heritage

Report Title; Environmental Constraints Report - Cultural Heritage

Report Number; B14000AG-BORStudy-603

Revision; 1.0

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Appendix F. Geo-environmental Desk Study

Report Title; Geo-environmental Desk Study

Report Number; B14000AG-1005

Revision; 0

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Appendix G. Drawings & Concept Plan

Drawings Number Rev Drawing Title

B14000AG/BORStudy/1008 0 Initial Stream Route Alignment drawing

B14000AG/BORStudy/1009 0 Initial Stream Route Alignment drawing – Tree planting Buffer Zone

B14000AG/BORStudy/1010 0 Initial Stream Route Cross Sections

B14000AG/BORStudy/710 0 Location Plan

B14000AG/BORStudy/711 0 Geological Section 1-1

B14000AG/BORStudy/712 0 Geological Section 2-2

B14000AG/BORStudy/713 0 Geological Section 3-3

B14000AG/BORStudy/714 0 Geological Section 4-4

B14000AG/BORStudy/715 0 Geological Section 5-5

B14000AG/BORStudy/716 0 Geological Section 6-6

B14000AG/BORStudy/502 1 Pipeline Routes Terrestrial Ecology

B14000AG/BORStudy/503 1 Broad Oak Reservoir Water Pipelines

B14000AG/BORStudy/504 2 Pipeline Routes Landscape & Public Recreation

B14000AG/BORStudy/505 2 Pipeline Routes Flood Risk, Land, Grade Pollution & Cultural Heritage

B14000AG/BORStudy/604 0 Proposed Stream Diversion Corridor Planting Strategy

B14000AG/BORStudy/605 0 Proposed Stream Diversion Corridor Planting Strategy Considering

NG Pylon Proposal

Previous work – 2014 concept plan

Document Title Rev

Broad Oak Concept Plan Stage 3 Landscape and Ecology Vision 0.3 Issued November 2014

(includes the Concept Plan drawings)

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Appendix H. Pipeline Data Sources Summary

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