Environment Agency The Middle and Lower Stour and Moors River Ecological Vision and Restoration Measures
Hyder Consulting (UK) Limited 2212959 The Mill Brimscombe Port Stroud Glos GL5 2QG United Kingdom Tel: +44 (0)1453 423 100 Fax: +44 (0)1453 887 979 www.hyderconsulting.com
Environment Agency The Lower and Middle Stour and Moors River Ecological Vision and Restoration Measures
Author Mark Lang
Checker Bruce Lascelles
Approver Bruce Lascelles
Report No 002-GL-UA004077-03
Date 26th September 2012
This report has been prepared for the Environment Agency and Natural England in accordance with the terms and conditions of appointment for Broad Ecological Vision and Restoration Measures dated 26/10/2011. Hyder Consulting (UK) Limited (2212959) cannot accept any responsibility for any use of or reliance on the contents of this report by any third party.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959
CONTENTS
SUMMARY ...... 2 Part A 4 1 Introduction ...... 4 1.1 Survey area ...... 4 1.2 What is meant by an ecological ‘vision’ ...... 6 1.3 Key Legislative and Policy Drivers ...... 6 1.4 Survey Methodology ...... 9 PART B ...... 12 2 Introduction to the Middle and Lower Stour ...... 13 2.1 Geology and soils ...... 13 2.2 Geomorphology ...... 13 2.3 Catchment land use ...... 14 2.4 Habitats and species ...... 15 2.5 Water quality ...... 16 2.6 Landscape and recreation ...... 16 2.7 Fisheries ...... 16 2.8 Physical modifications ...... 17 2.9 Long term ecological vision for the Middle and Lower Stour ...... 29 2.10 Conclusions from the ecological vision ...... 38 PART C ...... 39 3 Introduction to the Moors River System ...... 40 3.1 Introduction ...... 40 3.2 Geology and Soils ...... 40 3.3 Geomorphology ...... 40 3.4 Catchment land use ...... 43 3.5 Habitats and species ...... 43 3.6 Water Quality and resources ...... 46 3.7 Landscape and recreation ...... 46 3.8 Fisheries ...... 46 3.9 Physical Modifications ...... 46 3.10 Long term ecological vision for the Moors River System ...... 51 3.11 Description of the Moors system once the ecological vision is implemented ...... 61 3.12 Conclusions from the ecological vision ...... 62
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page i
4 References ...... 63
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page ii
SUMMARY
Hyder were contracted by the Environment Agency to undertake a study of the Middle and Lower River Stour (the Main River only) and Moors River system in Dorset. In order to inform the study a survey was carried out which involved walking the banks of both rivers, recording key geomorphological features, the extent of physical modification that each river has been subject to and providing recommendations for enhancement measures to restore each river to a more natural state and allow the expression of the characteristic habitat form and function for the benefit of the flora and fauna characteristic of the river type. The main driver for this work is the onus on the Environment Agency to seek improvement to rivers and watercourses under the Water Framework Directive (WFD), in addition to other statutory drivers.
The walkover study identified that the Middle and Lower Stour has been subject to significant historical artificial modifications, including dredging and channel realignment for flood defence and other purposes. In addition, there are a number of weir structures causing impoundment to flows. This has resulted in large sections of the channel being relatively uniform (wide and often deep), with the channel form lacking a diverse morphology.
By contrast, The Moors River System is essentially a natural system exhibiting an exceptionally diverse range of aquatic and wetland vegetation. On a local scale the river has, in the past, been modified to provide water for mills, trout lakes and for watercress cultivation. In the southern reaches of the river, below Verwood, discrete lengths have been dredged and realigned for agriculture, flood alleviation and urban drainage. In addition, until recently, weed cutting in the channel took place to increase drainage capacity.
Following the completion of the survey an ecological vision was drawn up for each river. The ecological vision aims to present a definition of what good ecological status on both rivers should look like, the objective being for each river to exhibit the biological, chemical and structural characteristics that would be expected under nearly undisturbed conditions (i.e. in a natural, unmodified state what should both rivers look like, and what habitats, species and geomorphology would be expected).
It is beyond the remit of this report to comment in detail on the potential effects of climate change. However, it is worth noting that the restoration measures proposed have the potential to increase the resilience of the River Stour and Moors River to the effects of climate change, as well as providing a number of additional benefits.
Restoration suggestions for the Stour have focused on the removal of structures such as weirs, where possible, and physical intervention to restore diversity to the channel and improve connectivity with the surrounding floodplain. For the Moors River, restoration measures have focused more on management of adjacent habitats rather than extensive physical restoration of the channel itself.
Although both rivers would benefit from the implementation of restoration measures, it was apparent that both currently support a diverse range of wildlife. The measures proposed aim to build on the wealth of biodiversity that already exists.
This report presents the survey methodology and the broad ecological vision for the Middle and Lower Stour and the Moors River. The report has been divided into three sections:
. Part A Introduction and generic information applicable to both rivers . Part B Introduction to and ecological vision for the Middle and Lower Stour . Part C Introduction to and ecological vision for the Moors River System
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 2
Following on from this report, detailed reach by reach restoration plans have been produced for each river. These plans are the subject of a separate report.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 3
Part A 1 Introduction 1.1 Survey area
This report presents the results of a geomorphological and ecological survey of the Middle and Lower Stour and the Moors River System in Dorset. This report presents a broad overview of the main physical habitat modifications that each river has been subject to, the impact of these on the ecology of the rivers and a broad overview of actions that could be undertaken to improve the habitat condition of each river.
Following the production of this report, a series of reach by reach restoration measures will be identified, together with a high level consideration of the potential flood risk implications. This will be set out in a separate report.
The section of the River Stour that this report is concerned with is from the confluence of the River Lydden, upstream of Sturminster Newton, downstream to Christchurch. Upstream of Wimborne Minster the river is known as the Middle Stour; whilst downstream it is known as the Lower Stour.
The survey for the Moors River System includes the river from Cranborne (where it is called the River Crane) downstream to the confluence with the Lower Stour, and included the tributaries the Mannington Brook and the Uddens Water.
Figure 1 shows the extent of the survey area with the reach numbers used in this report.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 4
Figure 1: Extent of the study area (Middle and Lower Stour and Moors River System)
Moors River System – Mannington Brook Moors River Middle System Stour
Moors River System – Uddens Water
Lower Stour
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 5
1.2 What is meant by an ecological ‘vision’
Natural England, in collaboration with the Environment Agency, has developed guidelines for generating strategic physical restoration plans for Sites of Special Scientific Interest (SSSI) rivers (Mainstone, 2007; and Sears et al. 2008). Whole-river restoration plans are required for river SSSIs for which physical modification is identified as a reason for ‘Unfavourable Condition’. As the first part of this process, Natural England suggest the production of an overarching, high- level ecological vision of what restoration to favourable condition should seek to achieve, in terms of geomorphological form and function, habitat provision and visual character. The aims of these high- level ecological visions are four-fold:
To identify and evaluate the physical modifications that have led to reduced habitat provision for characteristic biological communities;
To assess the ecological consequences of these modifications, focussing on the components which have been most significantly affected;
To prepare a high-level, long-term ecological vision for the river, in its restored state, based on the assessment of ecological consequences arising from physical modifications. The ecological vision would describe the desired improvements in habitat provision and the anticipated benefits to the characteristic flora and fauna of the river; and
To draft a schedule of possible approaches to restoration, recognising and utilising natural recovery processes as far as possible. Proposed approaches to restoration would be accompanied by specific examples and case studies, where available.
Although this process is targeted at rivers designated as SSSI, it can be extended to include non- designated rivers such as the River Stour. It is intended that these ecological visions will provide a foundation for subsequent detailed river geomorphological evaluation/interpretation and whole-river restoration planning.
This report outlines the ecological vision that has been produced for the Middle and Lower Stour and the Moors River System, including the Moors River SSSI. 1.3 Key Legislative and Policy Drivers
There are a number of pieces of legislation and other policy drivers that underpin this ecological vision. It is considered outside the scope of this document to detail all relevant legislation, but a number of pertinent points are summarised below. 1.3.1 The Water Framework Directive (WFD)
This Directive requires that all surface and ground waters within defined River Basin Districts must reach at least ‘good ecological status/potential ’ in a series of reporting cycles (the first being 2015 running up to 2027). ‘Good ecological status’ is defined as a river (or other surface water body) having the biological, structural and chemical characteristics similar to those expected under natural nearly undisturbed conditions. The ecological potential of a water body represents the degree to which the quality of the water body’s aquatic ecosystem approaches the maximum it could achieve, given the heavily modified and artificial characteristics of the water body that are necessary for the use or for the protection of the wider environment.
The Environment Agency has produced a River Basin Management Plan (RBMP) for the South West River Basin (incorporating the Dorset River Basin Area) highlighting how the WFD requirement will be undertaken (The Water Framework Directive 2000, Environment Agency The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 6
2009). There are 102 river water bodies in the South West River Basin with a combined length of 890km, and one lake. Currently, 43%of surface waters (318km or 36% of river length and the lake, Little Sea) achieve good or better ecological status/potential. Waters at good status now include the Crane (part of the Moors River System), the Cale and the upper Piddle. The main reasons for less than good status are:
High levels of phosphate,
Impacted fish communities,
Low levels of dissolved oxygen
Physical modification.
Of the surface waters assessed for biology, 58% are at good or high biological status now.
The Environment Agency has split the Dorset River Basin Area into a number of separate units, each with a reference number. For the purposes of this report, the Middle Stour includes WFD units R49 and R63, the Lower Stour unit R61 and the Moors River System unit R62.
The WFD objectives for these units are given in Table 1 below:
WFD Unit WFD Status Failing elements Objective
Middle Stour (WFD Overall Moderate Status limited by To achieve good ecological unit R49) phosphate/phytobenthos status by 2027 Fish – Moderate Good chemical status by 2015 Invertebrates - High
Lower Stour (WFD Overall Poor Status limited by To achieve good ecological unit R61) phosphate/phytobenthos status by 2027 Fish – Moderate Good chemical status by 2015 Invertebrates - High
Moors River Poor Fish populations To achieve good ecological System (WFD unit status by 2027 62) Fish – Poor
Invertebrates - Moderate
River Crane (part Overall Good of the Moors River) Fish – Good
Invertebrates - Good
Previously under the WFD, the Lower Stour was designated as a heavily modified water body (HMWB). The WFD definition for artificial water bodies (AWB) and heavily modified water
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 7
bodies were revised in 2011. In order for a river to be classed as an AWB or HMWB a river has to:
Have an existing and specified use(s); and
Have physical modifications connected to those uses; and
Those physical modifications adversely affecting the stays of the ecology; and
Be impossible to reach good ecological status without restoration and mitigation to those physical modifications; and
That restoration would significantly adversely affecting the use(s); and
Those physical modifications are the only means to deliver the use.
Under the revised definitions, the Lower Stour (downstream of Wimborne Minster) is no longer classified as a HMWB, and within the Dorset RBMP the majority of ecological receptors on the Stour (fish and invertebrates) are considered to already be at good ecological status; thus on paper it is difficult to justify further restoration. However, despite this the walkover survey has identified a range of factors impacting on both the Stour and Moors River and it is considered that restoration measures are still required in order for the both rivers to achieve good ecological status. 1.3.2 The Eels Regulations (England and Wales) 2009
This legislation (The Eels (England and Wales) Regulations 2009) implements European Council Regulation EC No. 1100/2007 of 18 September 2007, establishing measures for the recovery of the stock of European Eel. The Regulations require Member States to implement a number of short- and long-term measures (for example the provision of eel ladders at barriers to migration) to achieve a target of ensuring that at least 40% of the potential production of adult eels return to the sea to spawn on an annual basis.
In order to implement the targets outlined in this legislation, an eel action plan has been produced for the South West River Basin Management Plan (Environment Agency, 2010). This identified that the main issues for the RBD are lower glass eel recruitment, and reductions in the amount of habitat available to eels because of migration barriers. Therefore, the ecological vision has included a focus on the lowering or removal of migration barriers. 1.3.3 Sites of Special Scientific Interest (SSSI)
Part of the Moors River Catchment has been designated a SSSI, known as the Moors River System, but this designation does not include the tributaries the Mannington Brook or the Uddens Water. For the purposes of this report the term ‘Moors River System’ includes both the designated sections and the tributaries. The River Stour has not been designated as a SSSI.
The condition of the SSSI land in England is assessed by Natural England. There are six reportable condition categories: favourable; unfavourable recovering; unfavourable no change; unfavourable declining; part destroyed and destroyed.
The UK Government set a Public Service Agreement (PSA) target to improve 95% of Sites of Special Scientific Interest (SSSIs) to be in favourable condition by 2010. Natural England provided detailed information on the current ecological status of the Moors River System SSSI in the form of the draft Common Standards Monitoring Condition Assessment for the Moors River System (Natural England, Doug Kite 2009) and the conservation objectives for the Moors River System (Natural England, 2009). The Common Standards Monitoring programme details The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 8
how the ecological condition of SSSIs are monitored by the setting of conservation objectives for each SSSI and whether or not they are achieving good ecological status, i.e. whether or not the conservation objectives are being met.
Further details on the Moors River SSSI Citation are presented in Section C. 1.3.4 The Catchment Flood Management Plan
The Catchment Flood Management Plan (CFMP) for the Dorset Stour, including the Moors River System, produced by the Environment Agency (Environment Agency, 2009), sets policy options for the management of flood risk within the Stour catchment. The catchment has a long history of flooding, with at least 1% of the total population living in the catchment at risk from flooding (1:100 flood risk).
The restoration measures outlined in the ecological vision will have flood risk implications, both positive and negative. Whilst it is outside the scope of this document to review the restoration options against the policies outlined in the CFMP, this will be undertaken for the detailed reach by reach restoration options. 1.4 Survey Methodology 1.4.1 Desk Study
Existing information on the Middle and Lower River Stour and the Moors River system was reviewed. The sources of information and documents used are referenced in the text and listed in the references (see Section 8).
In addition, a meeting was held with the Environment Agency Operations Delivery and Asset Systems Management (ASM) Teams, who are responsible for regular maintenance work along the river, in order to understand the historic and current management work undertaken on the rivers. 1.4.2 Field Survey
A field survey was undertaken by walking the full length of both of the rivers within the study area (the survey of the Moors River included two tributaries, the Mannington Brook and Uddens Water), where access was possible. Efforts were made to contact all relevant landowners and gain approval to access their land. However, for a small number of locations it was not possible to gain access permission, and as such no direct survey work has been undertaken on these stretches.
The locations where access was not possible or only partial access was obtained are detailed below on Figure 3.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 9
Figure 3: Reaches not surveyed or only partially accessed (indicated by red triangle)
Moors River System Middle Stour
Lower Stour
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 10
For the locations where access was restricted, aerial photographs were studied in detail to gain an understanding of the nature of the channel and associated biodiversity, where visible.
The rivers were divided into a series of reaches (varying in length from 1-4km and divided on the basis of physical structures such as weirs or bridges). Physical data was collected as a series of point data on a handheld Geographical Positioning System (GPS). These data have been used to create a geomorphological database. The geomorphological database is a powerful tool, allowing the targeting of restoration measures within each river reach. In addition, for each reach, a recording sheet was completed summarising the geomorphological and ecological attributes and the restoration measures required.
The following examples give an indication of how the known geomorphology has been used to inform the reach by reach restoration plans (the subject of a separate report):
• Specific restoration measures have not been proposed where there is already a diversity of flow regimes and sediment accretions, as in these areas the river is already exhibiting a more natural form and function. Assisted natural recovery in these locations may be all that is required.
• Measures to narrow the channel and increase flow rates across part of the channel have been targeted in areas where no sediment accretions were visible or where existing coarse sediments were smothered by silt.
• Restoration measures aimed at diversifying channel morphology have focused on straight, uniform sections of channel.
• Where possible, bank re-profiling has been targeted on low lying areas where the greatest benefit from the creation of a new marginal zone would occur, such as the inside of large bends or where the adjacent land is low lying.
• Restoration solutions aimed at key physical modifications, such as weirs and hard artificial bank protection, can be targeted exactly.
Photographs were taken to illustrate the ecological vision and to record features at specific locations. It should be noted that photographs were not taken for every single geomorphological feature recorded. Due to the size of the photograph database these have been included as a separate CD to accompany this report.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 11
PART B
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 12
2 Introduction to the Middle and Lower Stour
The following sections provide an overview of the nature of the River Stour within the study area (see Figure 1). 2.1 Geology and soils
The Catchment Abstraction Management Strategy (CAMS) for the River Stour (Environment Agency, 2004) provides background details on the catchment as a whole:
‘Upstream of the study area, around Gillingham, the landform varies from expansive open landscapes to deep enclosed valleys running off the North Dorset Limestone Ridge and onto clay. Further west and south, the Blackmore Vale is broad and gently undulating, and is drained by the Stour and a dense network of tributaries. This is an agricultural landscape of pastures, scattered villages, hedgerows and small woodlands forming an irregular patchwork. Flowing south towards Sturminster Newton, the Stour is joined by several clay-influenced tributaries (including the Bow, Filley and Caudle Brooks, the Cam, the Lydden and the Divelish). The nature of the geology gives rise to a dense drainage network, which is particularly responsive to rainfall.
Below Sturminster Newton, the Stour flows towards Blandford Forum through a narrow valley with chalk hills on either side. The land use is mainly arable on the gentle slopes towards the edge of the floodplain and pasture on the flat valley floor. Settlements and roads tend to be concentrated on the valley floor or lower slopes of the chalk escarpment. Tributaries here are fewer in number but are important chalk stream rivers (including the Iwerne, Allen, Gussage, Tarrant, North Winterbourne and Pimperne Stream) which have an influence on the main channel. At Wimborne Minster, the Stour flows over the geological boundary onto the Tertiary deposits (mainly sands and gravels) and on towards Bournemouth across a landscape of typically large pasture and arable fields. At Wimborne the Stour is joined by the River Allen, which flows over chalk for almost all of its length. This valley is dominated by arable agriculture, with water meadows on either side of the river and frequent copses of riverside trees.’ 2.2 Geomorphology
The Middle and Lower Stour is considered to correspond to a lowland, low gradient river (Mainstone, 2007). Under conditions of low anthropogenic impact it is expected that bed materials would be dominated by sands and silts, with coarser gravels accumulating at glides. Flows would be dominated by glides, with considerable meandering expected with erosion and deposition leading to an alternating sequence of eroding cliffs and shallow banks and point bars. Occasional dams of coarse woody debris would be expected, creating short stretches of ponded flow and adding considerable diversity to the main river channel. There are, however, sections which do not conform so well to this designation, where gravels are present throughout the river, such as the reaches downstream from Blandford Forum.
However, the Stour has been heavily modified by human activities and does not quite exhibit the complete suite of geomorphological features that might be expected. The Stour responds rapidly to rainfall events; as a consequence of this large sections of the river have been dredged historically and there are a number of Flood Alleviation Schemes (FAS) on the river where there is routine removal of, for example, large woody debris.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 13
2.2.1 Geomorphology condition assessment
River Habitat Survey (RHS) data has been provided for the River Stour by the Environment Agency. These data show that the river has a range of Habitat Modification Scores (HMS) from 0 (near pristine) to 2480 (severely modified). These are then summed to give each stretch of river to a Habitat Modification Class; Classes 1 and 2 being relatively unmodified and Classes 4- 5 being heavily modified. Only a limited number of sections of each river (each 500m in length) have been subject to RHS survey, and more than one 500m section can be found in some of the reaches that the river was divided into for the purposes of this report. Therefore, it is difficult to build up a detailed picture as to the level of physical modification of the rivers as a whole from these data alone. Table 2 indicates the survey reaches where relatively unmodified sections have been recorded and where highly modified sections have been recorded.
Table 2: 500m Sections of relatively modified and unmodified river on the Middle and Lower Stour River Survey sections with Survey sections with relatively severely modified 500m unmodified 500m stretches stretches (HMC 4 and 5) (HMC 1 and 2)
Middle and RS18, RS20, RS27, RS30 RS4, RS5, RS6, RS8, RS15, Lower Stour RS23, RS26
During the walkover survey it was found that all of the survey reaches identified above would benefit from some form of restoration intervention and that the HMC’s were not particularly useful in predicting modified or unmodified river reaches. In general, it appears that unmodified and highly modified sections can occur within close proximity of each other. This may indicate that physical modifications are localised but may just reflect the widely scattered nature of the 500m sections subject to RHS.
The walkover survey concurs with the geomorphology description given in Section 2.2. To a large extent the Middle and Lower Stour conforms to a lowland, low gradient river with the associated features present to some degree. However, it is considered that physical modification due to dredging (over widening and deepening of the channel), channel realignment and impoundment of flows from weirs has limited the extent to which the river can erode and deposit in a natural manner. It is considered that this has resulted in large sections of the channel being fairly homogenous, exhibiting few of the geomorphological features that would be expected. 2.3 Catchment land use
The following draws on the CAMS for the River Stour (Environment Agency, 2004):
‘Upstream from Sturminster Newton the valley is quite narrow (~500m), with chalk hills either side. The surrounding land use is dominated by agriculturally improved pasture used for cattle grazing. At Hinton St Mary the floodplain on the eastern bank narrows due to a chalk outcrop and a small area of fen meadow and sedge bed is present adjacent to the river. The floodplain gradually widens on the approach to Blandford Forum, but chalk hills still define the valley sides, with the surrounding land use again being dominated by improved pasture (although there are occasional areas of riparian woodland on steep slopes adjacent to the river, for example just below Hod Hill). Below Blandford Forum the floodplain widens (to, on average, 1-2km wide) and is dominated by large, agriculturally improved pasture and arable interspersed with small copses. The Middle and Lower Stour below Wimborne Minster has considerable urban development as the river flows through the suburbs of Bournemouth.’ The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 14
As the majority of the floodplain has been subject to agricultural improvement, the connectivity to the floodplain is poor with very little natural wetland remaining in the floodplain. 2.4 Habitats and species
The Stour supports a diverse fish population, including Diadromous species (species that migrate from the sea to freshwater) such as sea trout (Salmo trutta) and salmon (Salmo salar), Catadromous species such as eels (Anguilla anguilla) which migrate from freshwater to the sea, and Potamodromous species, which live wholly within freshwater, such as bullhead (Cottus gobio).
There is relatively little information available concerning the other habitats and species present along the Middle and Lower Stour. The field survey has identified that the catchment is dominated by agriculturally improved pasture, supporting a low diversity of species. In the absence of fencing, grazing pressure extends right up to the river bank. Features such as patches of riparian woodland, fen and sedge bed and the occasional ditch or back channel, add to the biodiversity interest, but are extremely limited in extent. Due to physical modifications large sections of the river channel are relatively uniform.
Where the banks of the river are fenced, the riparian zone is dominated by emergent Common Reed (Phragmites australis) and ruderal weeds. Willow (Salix sp.) and Alder (Alnus glutinosa) are a feature of the riparian vegetation and in places are quite extensive. These trees help to trap sediment, creating large side bars and berms whilst providing a source of large woody debris to the river. These large silt bars diversify the channel, allowing a wider range of emergent flora to exist and, together with the large woody debris, are likely to support a diverse invertebrate assemblage. These features are, however, limited in extent.
The Environment Agency provided numerous records for otters (Lutra lutra) within the catchment and, during the field survey, otters were observed at Blandford Forum and otter droppings (spraint) were noted in numerous locations along the river. The Environment Agency also provided some limited information on the distribution of water voles (Arvicola amphibious). Suitable habitat was present in a number of locations where riparian vegetation was extensive, but these suitable reaches were fragmented due to grazing pressures and riparian trees shading out vegetation. The Environment Agency also advised that native white clawed crayfish (Austropotamobius pallipes) are still present in some of the headwaters of the River Stour, notably the tributary the River Allen. These are likely to decline in the long term due to the presence of the invasive signal crayfish (Pacifastacus leniusculus) (see section 2.4.1).
During the course of the field survey it was apparent that the river supported a diverse assemblage of birds, some resident and some winter visitors, including kingfisher (Alcedo atthis, with at least 1 bird noted per 2km of river); cormorant (Phalacrocorax carbo carbo and Phalacrocorax carbo sinensis - the latter subspecies being widely distributed and reported to be causing severe impacts on fish populations); little egret (Egretta garzetta); moorhen (Gallinula chloropus); mallard (Anas platyrhynchos); snipe (Gallinago gallinago, which was flushed from wet areas in the adjacent floodplain); and mute swans (Cygnus olor, with up to 200 noted grazing in the meadows below Wimborne Minster). 2.4.1 Non Native Invasive Species
The Environment Agency highlighted that non-native invasive species are becoming an issue of conservation concern on the Stour catchment. These include the American signal crayfish and plant species such as Himalayan balsam (Impatiens glandulifera).
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 15
It is outside the scope of this document to predict the potential effects of non-native species on native flora and flora, but it is an issue that the broad ecological vision will need to address in the long-term. For example, fencing out livestock from the river bank to encourage marginal vegetation may encourage the spread of non-native invasive plant species. A detailed review of the extent of spread of non-native species and an action plan for management recommendations is required. 2.4.2 Alder disease
Die back of alder trees caused by the fungus Phytophthora albi was noted in some locations along the Middle and Lower Stour. It is recommended that replacement of any loss of alders should be through the planting of Phytophthora resistant alder varieties or, if appropriate, additional native species of local provenance which are not susceptible to alder disease, such as willow and native black polar. 2.5 Water quality
The Environment Agency surface water monitoring has indicated that biological results for the River Stour are good, with 89% of the river achieving an A (very good, biology similar to an unpolluted river) or B grade (good, biology is slightly below that expected of an unpolluted river). Chemical water quality data indicate that 62% of the river was in the top two grades in 2000.
The RBMP indicates that the water quality of both the Middle and Lower Stour is limited by the presence of phosphates. It is considered that good farming practices, including the use of buffer strips along the river bank, will help lower chemical usage and transport to the aquatic environment, and will help deliver further water quality improvements along the river. This approach is advocated within the Defra Catchment Sensitive Farming Programme (see Section 2.8.1) 2.6 Landscape and recreation
The chalk landscape upstream of Blandford Forum is quite open, with large arable fields and small blocks of woodland on the valley sides and smaller improved pasture fields within the floodplain. Downstream of Blandford Forum the floodplain consists of large fields of improved pasture, with some arable cultivation and occasional blocks of riparian woodland where steep slopes have prevented agricultural intensification. Most of the upland areas around the upper catchment, largely outside of our project area, have been designated as an area of Outstanding Natural Beauty (AONB).
The River Stour is a well-used recreational resource, with the Stour Valley Way footpath providing public access to large sections of the river and, just outside Bournemouth; the Stour Valley Local Nature Reserve encompasses the river and riparian habitats. The river is also an important coarse fishery (see Section 2.7) and anglers have access to the majority of the river.
At Christchurch, the harbour offers a range of recreation activities with the limit of public navigation being Iford Bridge.
Several historic mills along the river provide a focus for informal recreation, for example the restored Sturminster Newton Mill. 2.7 Fisheries
The dominant fish assemblage on the Middle and Lower Stour consists of coarse fish including roach (Rutilus rutilus), pike (Esox lucius), dace (Leuciscus leuciscus), chub (Leuciscus
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 16
cephalus), barbel (Barbus barbus) and perch (Perca fluviatilis) and the river is a noted coarse fishery with fish spawning throughout the main river and the lower end of the tributaries, where there is suitable habitat. The Stour historically supported important freshwater eel and migratory salmon fisheries. However, in line with national declines and other factors, numbers of both species on the River Stour have declined drastically since the mid 1980’s. In addition, extensive dredging work in the 1960’s and 1970’s removed thousands of tonnes of gravel from the Lower Stour which eliminated spawning habitat for coarse species, such as barbell and chub, and salmonid species such as brown trout, sea trout and salmon. These works contributed to the collapse of the Stour as a salmon fishery and also impacted on species such as barbel, which need varying flows and associated habitats to complete their lifecycle successfully (information from the River Stour CAMS (Environment Agency, 2004) and Pers. Comm Jim Allan).
Tributaries of the main river, including the rivers Allen (particularly important historically for spawning salmon), Crane and Tarrant, are important spawning grounds for salmonid species, with some sections of the main river, for example around Wimborne and Spetisbury and downstream of the weirs at Longham and Throop, also used for salmonid spawning. The majority of salmon entering Christchurch Harbour ascend the Hampshire Avon on their way to spawning grounds on this system, and as a consequence the salmon (Salmo salar) population on the River Stour is low, with no evidence of salmon beyond Blandford Forum in the last 30 years. Brown trout (Salmo trutta) are present throughout the Stour river system, with the largest concentrations occurring where habitat is most suitable. Areas of favourable habitat include between Spetisbury and Wimborne Minster on the Lower Stour and tributaries including the Mannington Brook, the Tarrant, North Winterbourne and River Allen. The majority of the brown trout population is probably natural and wild and of considerable nature conservation value (Pers. Comm Jim Allan).
It is considered that the River Stour still supports a diverse coarse fishery. However, the lack of spawning habitat, barriers to the movement of fish caused by weirs and other structures and silt deposition on the remaining spawning gravels caused by impoundment of flows, again due to weirs and other structures, are likely to be having a detrimental effect on populations. In addition, poor quality spawning habitat is also likely to be having a negative impact on salmon and migratory trout populations. 2.8 Physical modifications
This section describes the physical modifications that the Middle and Lower Stour have been subject to, and Table 3 summarises the ecological consequences of these physical modifications. 2.8.1 Intensive agriculture and diffuse pollution
Although not a physical modification of the river channel, the land adjacent to the Middle and Lower Stour is dominated by agriculturally improved fields used for cattle grazing and in some locations arable farming. Intensive agriculture can result in high levels of nutrients and diffuse pollution entering the river and encouraging dense beds of nettles and other ruderal weed species in the riparian zone.
Diffuse pollution is recognised as a problem in the upper catchment such that it is a priority catchment under Defra’s Catchment Sensitive Farming Programme. During the course of the field survey it was apparent that large stretches of the river either had no marginal and riparian vegetation or had a very thin margin of vegetation due to fencing being located right up against the river bank. Additional selective fencing, set back from the river bank, would enable the creation of a buffer of riparian vegetation that would help prevent the ingress of diffuse pollution into the river.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 17
Intensive agriculture and drainage, together with overdredging, has resulted in poor connectivity between the river and the floodplain resulting in little natural wetland remaining in the floodplain. 2.8.2 Current Maintenance Work on the River Stour
Discussions with the Environment Agency Operations Delivery and Asset System Management Team, who are responsible for regular maintenance work along the river, highlighted that maintenance work along the Middle and Lower Stour has changed in recent years, with the focus moving away from land drainage, ensuring flood water leaves agricultural land as quickly as possible, to a focus on routine maintenance ensuring that the Flood Alleviation Schemes (FAS) function properly. Regular maintenance tasks are designed to ensure that the river channel has sufficient conveyance for flood water and that there is no net loss of storage capacity in the floodplain. Routine maintenance tasks include the clearing of debris from weir hatches and bridge arches and clearance for short distances upstream and downstream of the FAS schemes on the river, including those at Sturminster, Blandford Forum, Shapwick, Wimborne Minster and Christchurch (note this is not a complete list). 2.8.3 Historic maintenance work on the River Stour
Over widening and deepening (dredging) Historically, large sections of the river were dredged and de-silted to improve the conveyance of flood water within the channel for land drainage and flood defence purposes.
Information supplied by the Environment Agency and discussion with the Operations Delivery and Assets Systems Management Teams indicated that extensive dredging work in the 1960’s and 1970’s removed thousands of tonnes of gravel from the Lower Stour for flood risk management purposes, leaving a featureless linear channel (Figure 4). For example, in the 1960’s the whole river was dredged between Julians Bridge (at Wimborne Minster) and Canford Bridge and from Longham to Christchurch in the 1970’s, removing hugely significant in-channel habitat. The removal of these gravels eliminated spawning habitat for coarse species, brown trout, sea trout and salmon. In addition, the removal of large quantities of coarse bed material will have constrained the river to the middle of its channel, creating a uniform flow regime.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 18
Figure 4 (A) Historical dredging at Throop
Figure 4 (B) Continued Manor farm dredged channel in the 1970’s
(Photographs courtesy of Jim Allan, Environment Agency)
As a result of dredging, the main river channel has become relatively uniform, with flows dominated by glides and very little active meandering of the channel, as would be expected under more natural conditions. This situation is exacerbated upstream of some of the larger weirs where the slow flowing, uniform channel can extend for several kilometres upstream. Examples of this occur upstream of Throop Weir and Longham Weir as shown in Figure 5.
Figure 5: Dredged channel within Iford FAS (Photograph courtesy Jim Allen).
In addition to the slowing of flows and the creation of a uniform channel, over widening and deepening has the effect of lowering the level of the river in relation to the surrounding floodplain. This can cause the main channel to become hydrologically disconnected from the floodplain and wetland features such as ditches, back channels and ox bow lakes. Although in places the river has re-naturalised to some degree, routine dredging works still take place further downstream for flood risk management purposes, such as for the maintenance of the Christchurch FAS. As a result, flood water is less likely to spill out into the surrounding floodplain restricting the development of transitional wetland areas and wetland habitat. These past and on-going works restrict the opportunity for these heavily modified areas of the river to The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 19
naturalise, as valuable overhanging tree cover and marginal vegetation has to be removed before channel dredging operations can take place (Figure 6).
A B
Figure 6 (A) Tree clearance prior to dredging within the Christchurch FAS and (B) dredged channel within Iford FAS (Photographs courtesy of Jim Allan, Environment Agency) 2.8.4 Weirs
There are a number of weirs on the Middle and Lower Stour, ranging from historical structures designed to retain a head of water for a mill, to more recent structures used for gauging stations or rubble structures introduced to maintain a head of water within the channel as a consequence of over dredging in the past.
The presence of weirs has a large impact on the natural functioning of a river and characteristic species as indicated by Figure 7. Note this example is from the River Lugg in Herefordshire but it illustrates the process well.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 20
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 21
Figure 8 Examples of the types of weir structures present on the River Stour
Historic Mill and Weir at Large gauging weir at Throop Rubble weir above Sturminster Newton built to Ensbury Bridge service the mill.
As Figure 7 shows, downstream of major weir structures plunge pools and often small gravel bars (or other sediment deposits) can form. These features are beneficial to fish species such as trout, salmon and rheophilic (those fish requiring riffles and gravel habitats) coarse fish species, which may spawn on the gravel bars. However, the positive aspects of the weirs are at the expense of considerable lengths of slow flowing impounded water upstream (see Figure 9), possibly exacerbated by historical dredging works. The areas of impounded water encourage the deposition of fine silt particles, which can smother spawning gravels.
Figure 9 Impoundment upstream of Throop Mill
A further consequence of weirs is that they act as an effective trap, preventing the movement of coarse sediment along the river and the formation of the geomorphological features that would be expected in a less modified channel.
In addition, many of the major structures will also pose a barrier to movement within the river of other fish species, such as eels and coarse fish, and in particular small species such as bullhead. In order to help address this issue an eel pass has recently (2011) been fitted to the gauging weir at Throop. Many of the weirs have a small bypass channel often with an additional small weir or sluice; however, many of these bypass channels may also be impassable to coarse fish and eels (depending on the species).
It is considered that all the weirs on the River Stour downstream of Blanford Forum are either accessible for migratory trout or salmon or contain a dedicated fish pass. For example, Longham weir and Canford Weir have dedicated salmon passes fitted on one of the structures within the weir complex as a bypass, whilst weirs such as Keynston Mill and Clapcotts are
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 22
already accessible to salmon and sea trout. Bryanston Weir at Blandford is impassable to salmon and migratory trout. Figure 10 illustrates a number of the weirs mentioned
A B
Figure 10 Salmon pass on (A) Canford Weir and (B) salmon attempting to run Bryanston Weir in 1963 (Photograph courtesy Jim Allan Environment Agency)
It is considered that the rubble weirs, such as that above Ensbury Bridge, are relatively permeable and do not cause the significant impoundment noted behind the larger structures. The smaller rubble weirs diversify flow conditions, do not constitute a significant barrier to migrating fish and can be regarded as a positive contribution to the diversity of the river channel, and as such should remain in place.
It should be noted that some of the weirs are historical structures and likely to have significant cultural heritage value, whilst others are critical pieces of infrastructure, such as gauging stations, that will not be able to be removed or altered in the medium- to long-term; however, this should be reviewed when these structures have come to the end of their working life. Therefore, careful planning will be required to assess the relative importance and significance of each weir and determine the appropriate management option over the lifetime of the ecological vision. 2.8.5 Bridges
There are a number of bridges across the Middle and Lower Stour. The majority of the modern structures are single span and, as they have no structures in the channel, do not directly affect the river or pose a barrier to migrating fish. Of some interest are the historical arched bridges which, due to part of the structure being in the channel, directly affect the flow regime of the river, slowing flows upstream behind the bridge pillars and promoting the development of gravel bars and riffle flows on the downstream side (see Figure 11 for example).
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 23
Figure 11 Development of gravel bars and riffle flow below Crawford Bridge.
2.8.6 Channel realignment
There is clear evidence, for example long straight sections of channel with no sinuosity, that in many places the main river channel of the Middle and Lower Stour has been realigned. There are also indications that realignment has taken place at other locations, although it can be difficult to ascertain this on the ground, particularly where there are also obvious natural physical constraints to the channel alignment, such as an escarpment or low hill. However, from the evidence available from the field surveys and the information from the Environment Agency it is clear that many sections have been modified, and even where constrained by topography there are examples where this alignment is not totally natural. Often, there are traces of a historical sinuous channel evident in the fields within the floodplain.
The effects of channel realignment are similar to those caused by dredging and result in a uniform channel with a low diversity of flow regimes and in-channel features. 2.8.7 Adjacent land-use
Although not a physical modification to the river channel, the land adjacent to the Middle and Lower Stour is dominated by agriculturally improved fields used for cattle grazing. In the absence of fencing, the grazing extends right up to the riverbank and has restricted the establishment of riparian vegetation. In addition, localised access along the river bank has resulted in poaching and subsequent erosion, resulting in fine sediment entering the river, particularly in the upper reaches. However, in some situations limited poaching can prove beneficial where steep banks are moderated, creating low lying marginal zones, narrowing of the channel and creating fish fry refuge areas (see Figure 12 showing Crown Meadows upstream of Blanford Forum).
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 24
A B
Figure 12 (A) Cattle poaching creating marginal zone and (B) fry refuge area (fenced cattle drink) at Crown Meadows upstream of Blanford Forum. (Photograph courtesy Jim Allan Environment Agency)
As the river becomes wider and deeper, the banks are more usually fenced to stop stock from entering the watercourse, but in many instances the fencing is along the top of the bank and so limits the establishment of a wide buffer of vegetation. Where the fencing is set back from the river bank, a wide and diverse margin of riparian vegetation is often established which will help reduce sediment inputs to the river. In addition, the creation of dedicated cattle drinks limits the extent of poaching whilst also creating marginal dead water suitable for fish fry. Examples of the impact of grazing pressure on the river are shown in Figure 13.
Figure 13 (A) Examples of sections of the river with fencing (and a diverse buffer of riparian vegetation) and (B) without fencing (note lack of vegetation and erosion).
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 25
A B
Although, not a direct physical modification to the river, diffuse pollution is recognised as a problem in the upper catchment, such that it is a priority catchment under Defra’s Catchment Sensitive Farming Programme. During the course of the field survey it was apparent that large stretches of the river either had no marginal and riparian vegetation or had a very thin margin of vegetation due to fencing being right up against the river bank. Additional selective fencing, set back from the river bank, would enable the creation of a buffer of riparian vegetation that would help prevent the ingress of diffuse pollution into the river.
Other riparian land uses noted included woodland, golf courses and two country parks.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 26
2.8.8 Summary of physical modifications and their ecological consequences
This section discusses the broad ecological consequences of the physical modifications to the river that have been identified. It should be noted that the physical modifications can potentially have both negative and positive impacts on the ecological status of the river, particularly at the local scale. Table 3 identifies the physical modifications identified and the broad ecological and geomorphology consequences associated with them.
Table 3 Summary of physical modifications and ecological consequences Physical Ecological and geomorphological consequences Modification
Weirs Often act as a significant barrier to fish migration.
Lead to slowing of flows and upstream ponding of water and reduction of diversity of in-channel flow regimes and erosion and deposition features (such as gravel bars) limiting the flora and fauna that these features support.
Lack of fast flows limits the scouring of gravels which can become covered in fine sediment reducing suitability for fish to spawn.
Lack of faster flows limits the lateral movement of the channel planform through erosion and deposition, limiting the diversity of geomorphological features present (such as side bars and point bars) and limiting the flora and fauna that require these features.
Bridges Historic stone arch bridges can cause short sections of ponding upstream, particularly where there is a stone plinth associated with the bridge limiting the diversity of geomorphological features present (such as side bars and point bars) and limiting the flora and fauna that require these features.
Can cause channel pinching and an increase in flow rates which can be beneficial by keeping spawning gravels free of silt.
Downstream of arched bridges these variations in flow encourage the formation of gravel bars and riffle features important spawning grounds for roach and other fish species.
Where there is a stone plinth (apron) below the bridge this can cause a barrier to the in-river migration of small fish species such as bullheads.
Over widening Leads to slowing of flows and reduction of in-channel and deepening diversity.
Over wide channels leads to a lack of narrow fast flows
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 27
Physical Ecological and geomorphological consequences Modification
which would scour and keep spawning gravels clean.
Causes fine silt sediment to be deposited over gravels and other coarse bed sediments reducing their suitability for fish spawning.
Deep water prevents the establishment of in-channel emergent vegetation.
Channel Leads to reduction of in-channel diversity. realignment Over wide channels lead to a lack of narrow fast flows which would scour and keep spawning gravels clean.
Causes fine silt sediment to be deposited over gravels and other coarse bed sediments.
Deep water prevents the establishment of in-channel emergent vegetation.
Often associated with bank protection which limits the generation of material, eroding banks etc. This can be negative as it limits the supply of such material to the river reducing the physical features created such as gravel bars but beneficial if it reduces fine sediment input.
Grazing, Intensive grazing and lack of fencing can suppress the agricultural establishment of diverse riparian vegetation. improvement and riparian Local poaching and erosion causing fine sediment to enter vegetation the river which can smother spawning gravels.
Poaching can be beneficial in some locations, causing channel pinching (causing a variation in flow regime) and creating marginal dead water for fish fry habitat.
Fencing set back from the river bank aids riparian vegetation establishment.
Creation of cattle drinks limits poaching and creates marginal dead water and fry habitat.
2.8.9 Existing physical restoration measures
The Environment Agency provided details of a variety of restoration projects that have been undertaken throughout the Stour catchment and its tributaries, aiming to improve the conditions for coarse and salmonid fish species. These projects had, amongst others, the following broad aims:
. Increase the recruitment and retention of juvenile fish species by improving flood refuge habitat by creating back channels and dead water habitat as fish fry refuge areas;
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 28
. Improving the passage of fish species along the river by removing or modifying potential barriers; . Enhance existing spawning areas and increase potential spawning habitat including the provisions of new gravel substrates on the river bed; . Increase low velocity water areas as fish fry habitat/refuge; . Re-instate collapsed banks and re-profile weir pool to increase the weir pool habitat and variety of flow dynamics to benefit adult fish; . Creation of habitat for fish to congregate and allow angling access , modification and reduced cattle poaching. A selection of these projects has been highlighted in the ecological vision for the Middle and Lower Stour.
There has also been a focus on measures to improve water quality in the wider River Stour catchment, such as through the Defra Stour Catchment Sensitive Farming Approach. The Dorset Stour catchment is included as a priority catchment within The Catchment Sensitive Farming Capital Grant Scheme. This is offered to land managers in the priority catchments to support the improvement or installation of facilities that would benefit water quality by reducing diffuse pollution from agriculture. There are a range of capital items available, such as watercourse fencing, roofing for manure stores and pesticide loading and wash down areas. 2.9 Long term ecological vision for the Middle and Lower Stour 2.9.1 How the ecological vision has been developed
The Middle and Lower Stour has been subject to significant historical artificial modifications, including dredging and channel realignment for flood defence which, to some extent, still occurs on parts of the Lower Stour. In addition, a number of weir structures are present, causing impoundment to flows. This has resulted in large sections of the channel being relatively uniform (wide and often deep) and the channel form is lacking a diverse morphology. In addition, the surrounding catchment has been agriculturally improved such that there is very little connectivity to the floodplain and very little wetland remaining in the floodplain. Grazing and a lack of fencing have, in some sections, restricted the establishment of diverse riparian vegetation.
It is clear from the previous discussions that the modifications to the channel have had an impact on the functioning of the river and its tributaries, and thus the ecology supported at any given location.
To develop an ecological vision it is necessary to identify the ‘natural’ target condition of the river and range of ecological features such conditions should support. It is, therefore, possible to identify what the Middle and Lower Stour should look like if it were entirely natural, and what characteristic ecology it should support. However, in the following discussion it is important to note that changes to the physical structure of the river will not necessarily alter the impact of other factors, in particular poor water quality, on the river’s ecology.
Table 4 below summarises the target natural geomorphological features and associated characteristic ecology that would be expected for the Stour river type in the absence of physical modifications, together with a summary of the measures required to restore the river back to this more natural state. This is based partly on the generic descriptions for river types produced by Natural England (Mainstone 2007) and observations as a result of the field survey
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 29
Table 4 Typical geomorphology and ecological characteristics that could be expected for the Middle and Lower Stour River Type Summary of typical Geomorphology Summary of characteristic ecology Summary of restoration requirements
Type I – Lowland, low These two river types have close affinity, in River bed gravels or other coarse substrate provide an Sparse coarse bed materials so restoration required to gradient rivers having low gradient catchments and river essential but generally scant habitat for a wide variety of reinstate this type of material to create new gravel beds. channels running over clay or alluvium invertebrate and fish species in these river types, And (sometimes chalk). Stream power is somewhat including caddis-flies, riffle-beetles and mayflies, and a Flow regimes uniform lacking occasional pools and riffle variable but is generally low. diverse fish assemblage such as dace, bullheads, stone- flows. Channel narrowing would create areas of faster Type II – Lowland, loach (Barbatula barbatula), brook lamprey (Lampetra riffled flow. Removal of weirs would remove ponding of clay-dominated rivers Under conditions of low anthropogenic impact, planeri), minnow (Phoxinus phoxinus ), barbel, salmoid water and encourage more flow diversity. bed materials are likely to be dominated by silts species and stickleback (Gasterosteus aculeatus). and sands, with coarser gravels accumulating at riffles to an extent dependent on upstream On those sections naturally supporting a sufficient extent of sources of coarse substrate and the stream gravels, brown trout and some stonefly species of the Species characteristic of swift flows, such as water power generated by the catchment. Flow Leuctridae and Nemouridae families (which are more tolerant crowfoot, sparse in distribution due to lack of swift riffled patterns are likely to be dominated by glides, of silty substrates than other stoneflies) would flow. Restoration should aim to narrow channel to with coarser substrates underlying occasional characteristically occur. Gravels and swifter flows also promote faster riffled flow. riffles and finer materials underlying deeper provide rooting opportunities for species such as water- pools. crowfoot (Ranunculus penicillatus subsp. pseudofluitans) and water-milfoil (Myriophyllum spicatum), with an attendant Logs jams sparse due to regular clearance of the river Occasional log-jams would be expected to fauna. channel. In general a lack of large woody debris in the generate stretches of ponded water, to an extent river. Reduce channel maintenance and increase quantify depending on exact gradient, providing In general, in physical terms, the diversity of the in-stream of large woody debris in the channel. additional and important habitat variability. In fauna of rivers in these types will be largely dependent on the quieter sections backwaters with finer substrates extent to which the naturally occurring coarser substrates may occur. have been retained, and maintained in good condition (i.e. without excessive siltation). In quieter sections and Considerable meandering can be expected in backwaters with finer substrates, a flora and fauna more these types depending on natural sediment associated with stillwaters develops, including unionid River relatively uniform and lacking the physical diversity supply and hydraulic energy, generating mussels and pea-mussels, Libellulid dragonflies, agrionid that would occur with coarser bed substrates, therefore sequences of alternating steep and shallow bank damselflies, burrowing mayflies, water-snails, alderflies, and lacking a diverse in-stream fauna due to over dredging. In profiles which may lead to vertical cliffs (in less various families of caddis-fly (such as the Limnephilidae). The general the riparian fringe is lacking wetland vegetation so cohesive sediments) and point bars respectively. insect fauna is heavily dependent on an active marginal and restoration to increase floodplain connectivity and the wetland fringe of vegetation for hatching, resting, feeding and formation of transition wetland zones required. mating, and as a flow refuge under spate conditions.
Fish species may include perch, roach and eel, with chub, barbell, trout salmon and gudgeon where flows are stronger.
On shallow banksides (particularly the insides of meander Coarse fish present but weirs and other structures may be bends), a significant zone of hydrological transition can be limiting the movement of these species within the river. expected, with beds of emergent species such as branched Restoration should aim to remove these structures. bur-reed (Sparganium erectum) and reed canary grass (Phalaris arundinacea), and wetland species such as brook- Over dredging and lack of connectivity with the floodplain lime (Veronica beccabunga), water forget-me-not (Myosotis has largely removed the marginal zones where aquatic scorpioides), water-mint (Mentha aquatica) and water-cress vegetation can develop. However, in areas where silt is (Rorippa nasturtium-aquatica). Vertical cliffs provide nesting trapped by riparian willow trees is beginning to form silt opportunities for kingfisher and sand martins (Riparia riparia), berms on which wetland vegetation can develop but these as well as for burrowing bees and wasps and a range of other features are infrequent. insects specialising in bare soils. Water-voles thrive in bank sides of intermediate slopes with tall herb vegetation and an Erosion is still creating cliff faces for use by kingfishers active marginal zone of emergent plants. and sand martins.
Riparian trees provide an important additional habitat dimension, generating submerged exposed root systems that provide in-channel habitat for fish and invertebrates, potential holt and resting sites for otters, a source of woody debris and leaf litter for the river, and varying Distribution of riparian trees is limited and additional within-channel light and temperature regimes that add planting required maintaining and increasing the extent of further habitat diversity. this habitat type.
Riparian scrub provides additional important habitat for otter
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 30
River Type Summary of typical Geomorphology Summary of characteristic ecology Summary of restoration requirements
and bird species such as warblers and reed bunting. The co- occurrence of wooded and open river margins has been Riparian scrub is present but limited in its distribution, and shown to be important for a range of invertebrate species in additional planting required maintaining and increasing the chalk streams, and there is no reason to suspect these extent of this habitat type. species act any differently in other river types. Regular diurnal movements between the two habitats have been observed by a range of dipteran flies, caddis-flies and mayflies. Lack of floodplain connectivity means that there is very little inundation wetland remaining. Lowering bank levels On the wider floodplain, natural flooding regimes can be and other measures to increase flood plain connectivity expected to give rise to inundation wetland, particularly will increase the extent of this habitat type. alongside rivers with low base-flow, and fen and carr vegetation, particularly alongside high base-flow rivers.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 31
In order to address the issues identified in relation to physical modifications on the river, and restore the river to its target natural condition, a range of restoration measures will need to be implemented. 2.9.2 Restoration suggestions
The following outlines the suggestions to restore, as far as possible, the river to a near natural state.
A key issue to address will be to challenge specific constraints, such as historical flood risk management practices, to incorporate the adoption of new and novel ways of increasing habitat availability whilst reconnecting with the floodplain to also aid reducing flood risk. In addition, it will be important to monitor the restoration projects that have already been implemented on the Middle and Lower Stour and actively disseminate this information, highlighting both positive and negative aspects (if any) to angling clubs, River Trusts, Wildlife Trusts, Water Companies and other interested stakeholders.
The restoration approach has been divided into the following broad categories:
. Adaptive management - involves the modification of existing land management practices to promote the development of habitat conditions beneficial to the flora and fauna characteristic of the river. . Physical rehabilitation - involves physical intervention, often using machinery, to restore channel features to a more natural state following historical degradation. . Managing Control Structures- involves the management of structures that control water levels and distribution within the river corridor. Further details on each of these are presented below.
Adaptive Management . Reduce agricultural intensity on land adjacent to the channel and more widely through the catchment through continued support of the Defra Catchment Sensitive Farming Programme for the Stour catchment. . Increasing the quantity of locally derived large woody debris within the channel (in those sections where coarse woody debris is lacking) by felling and coppicing riparian trees and fixing the material generated to the bed and banks of the river. This will promote localised scour and sediment deposition, encouraging habitat diversity. . Selective, additional fencing of river banks to restrict access by stock and allow the establishment of riparian vegetation. . Creation of dedicated cattle drinking points to limit poaching and create marginal dead water fish fry habitat. . Set back of existing fencing to allow the creation of a wider riparian zone. . A limited programme of riparian tree planting, where appropriate, on those sections of river with largely open banks and a dearth of riparian trees to increase the supply of natural sources of large woody debris in the long-term and increase the extent of exposed bank side tree roots which offer refuges for a variety of aquatic flora and fauna.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 32
Physical Rehabilitation . The use of green/soft or bio-engineering techniques to narrow the width of the river and increase flow rates in selected locations to scour gravels clean and lead to the development of natural pool and riffle sequences. . Undertake projects at appropriate locations to increase in-channel diversity and enhance and increase spawning and fish fry habitat. . Undertake the continued reconnection of ditches and meanders, where present, to the river to establish hydraulic connection with the river and the creation of backwaters and marginal dead water. . Habitat creation within the limits of specific constraints, such as available space, flood risk etc. Habitat creation should focus on features such as fen, marshy grassland and carr habitats. These features, together with reconnection to the floodplain, may aid the storage of flood water contributing towards a lowering of flood risk. Managing Control Structures . Carry out a thorough review of the function, condition and status of all weirs, hatches and other control structures on the Lower and Middle Stour and develop an appropriate management strategy for each structure. . Where possible, allow to degrade, remove completely or remove sections of weirs where there are no/limited cultural heritage/flood protection constraints, and allow natural processes (both upstream and downstream) to re-assert their influence. . Downstream weirs to be removed first where possible, to allow channel to adjust and enable the effective management of flood risk consequences (if any). Such works should be carried out at an appropriate time. . If weir removal is not possible, for whatever reason, continue the programme of installing appropriate fish and eel passes on all structures that require them or consider the creation of effective by-pass channels to allow migrating fish to bypass the obstacle. Each obstacle should be reviewed on a case by case basis. 2.9.3 Aims and Objectives of the ecological vision
The aims and objectives of the ecological vision are set out in Table 5. Figure 14 highlights graphically how the biodiversity and geomorphology of the river is being restored to a more natural state, highlighting a number of key projects which have already been implemented (prior to the development of this ecological vision).
Finally, section 2.9.4 describes a sustainable, more naturally functioning Middle and Lower Stour. This is presented from the perspective of someone walking downstream (between Sturminster Newton and Christchurch), highlighting the physical features and associated wildlife that they could expect to experience. This, slightly romantic, portrait, is designed to give a feel for what the Middle and Lower Stour could look like once substantial restoration works have been implemented and the vision largely realised.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 33
Table 5 Aims of the ecological vision for the Middle and Lower River Stour Aims of Ecological Vision for the Middle and Lower
Dynamic
Geomorphologically active and capable of creating its own energy and diversity, increasing the quantity of gravels and other coarse sediments available as alluvial bars with reduced fine sediment deposition.
A channel with the freedom to change its planform (as far as possible given flood defence concerns and critical infrastructure) and cross section in response to active geomorphological processes.
The location and nature of individual geomorphological features will be dynamic; however, each reach will show representative examples of typical features which would be expected given the site-specific conditions. Where immovable constraints exist, the channel planform and cross section will be representative of natural processes within the limits of these constraints.
In good ecological condition
Naturally functioning and self-sustaining river system that exhibits a full range of characteristic habitats and species.
Sufficient extent of each habitat/species populations to enable the ecology to adapt in response to the dynamics of the channel.
Limited restrictions to the migration of species along the channel (at both low and high flows), through weir removal or, if not practicable, provision of suitable bypass channels. Channel sinuous and diverse, with numerous in channel features including narrow sections with fast flowing water such as riffles and significant quantities of clean gravels, together with slower flowing areas and deep pools. Riparian trees will continue to be a key feature of the river with significant quantities of coarse woody debris trapping silt and creating extensive side bars rich with emergent vegetation. In other places the channel will be more open with a diverse riparian flora.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 34
Connected to the floodplain Hydrological and physical connectivity between the river and its floodplain to enable the river to function, enhancing floodplain habitats, in particular marshy grassland, fen and wet woodland (carr) to expand. This will enable to use floodplain storage of water utilised as a benefit in relation to reduced downstream flood risk, ensuring that during high flows the river continues to gently overtop its banks and then drain freely back into the river channel. The wetter conditions created will enhance riparian habitats and consideration should be given to creating and reconnecting wetland features in the floodplain such as ditches, shallow scrapes, back channels, fen, carr and species rich grassland.
Resilient to change
Resilient to the effects of climate change.
Extent and diversity of habitats and species and their connectivity along the entire channel sufficient to allow adaptation to change.
Set within a cultural heritage and landscape setting
Retains features of significant heritage value within the river and floodplain setting (with adjustments where possible to remove the barrier effect of any structures), such that there is an appreciation of past and present land uses.
The natural form and dynamics of the channel complemented by low intensity adjacent land use and areas of semi-natural habitat.
Ensure continued public access and fishing usage respecting the cultural and historical importance of the river valley
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 35
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 36
2.9.4 Description of the Middle and Lower Stour once the ecological vision is implemented
The following section presents an idealised description of the restored river, walking downstream from Sturminster Newton towards Christchurch. This has been set out to provide a description of how the river may differ as a result of the proposed restoration measures.
The river is gently sinuous and is actively eroding in some sections and depositing this material further downstream, with a mixture of deep slow pools and shallow faster riffle flows, such as the extensive riffles and gravels below Blandford Forum. There are numerous shallow sections with gravel deposits, side bars or other in- channel features that reduce the width of the channel creating localised areas of faster flow that scour the gravels, keeping them free of silt. Large alder and willow trees are a frequent sight along the river bank and some have collapsed into the river. The tree branches and roots collect fine sediment creating large areas of sediment accumulation on which species-rich emergent vegetation is developed. These silt deposits divert flow, creating areas of marginal dead water close to the bank where fish fry can shelter, and faster flows in mid channel suitable for trout, barbel, grayling and other fish species.
Areas where riparian woodland exists adjacent to the river (often on steep slopes not suitable for agriculture) have been left to develop naturally. Large tree roots create suitable conditions for otters to rest and lie up, for example on the slopes of Hod Hill. There are also large open areas where trees are more widely spaced, with luxurious aquatic and emergent vegetation suitable for foraging water voles.
Fencing is set back from the bank top so that a wide buffer strip of riparian vegetation is present. Wetland features such as ditches and ox bows are connected with the river and habitat creation works have been undertaken to create additional features, such as ponds and shallow scrapes. There is hydrological connectivity between the river and adjacent fields which has resulted in the development of wet grassland and woodland habitats. These natural processes and wetland features aid the retention of floodwater in the floodplain and contribute towards reducing flood risk.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 37
Large weir structures, such as those at Durweston, Blandford Forum, Longham and Throop have been removed where possible, or have an effective fish pass so that migrating fish are able to bypass the weir. Small rubble weirs (constructed to retain water levels after over-dredging), that are relatively permeable to water flows, are not causing significant ponding of water or a significant barrier to migrating fish and have been left in place, diversifying the channel.
The public have access to the river for informal recreation such as walking the Stour Valley Way and accessing the Country Parks at Wimborne Minster and Ensbury, whilst fishing continues to be a major activity on the river. In key locations information boards explain how the restoration works have been undertaken and the benefits they are providing. 2.10 Conclusions from the ecological vision
The aims and objectives of the ecological vision are designed to be relatively firm and inform the reach by reach restoration action plan, which will be a flexible working document. The core restoration actions for the River Stour will include:
. Removal of weirs and other structures to remove barriers to fish passage and restore a diverse flow regime to the river. . Reinstate coarse bed materials such as gravels to promote the development of gravel beds and bars. . Narrow the channel through green engineering solutions, such as the introduction of large woody debris to increase the flows to keep gravels clean and promote the formation of riffles and other flow regimes. . Set back and lower flood banks to increase connectivity of the river with the floodplain, allowing the development of a transition zone and the establishment of riparian wetland vegetation. . Increase the levels of riparian trees and woodland. The action plan will take some years to implement as not all the aspirations will be readily achievable, at least in the short-term. It is recognised that some of the infrastructure present, such as weirs, may have significant cultural heritage value, or have a critical role, such as the gauging weirs used for flood prediction; therefore, removal of these features may not be possible. Following the broad ecological vision, reach by reach restoration options will be made for each section of the river. These restoration options will have flood defence implications which will be addressed within the reach by reach restoration report.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 38
PART C
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 39
3 Introduction to the Moors River System 3.1 Introduction
The Moors River system is a small lowland river which supports an exceptional diversity of aquatic and wetland plants. The river rises as a winterbourne on the chalk of the South Wessex Downs and is at first known as the River Crane. On the upper reaches the channel of the River Crane exemplifies a small chalk stream with a diverse and substantially natural habitat structure. Flows are dominated by shallow glides and riffles, with numerous gravel exposures. The River Crane becomes the Moors River below Verwood at the confluence with the Ebblake Stream. From this point the river becomes typical of a low gradient river with slower, more ponded flow in places caused by numerous woody debris log jams and silt deposition is more evident as opposed to clean gravels. Towards the confluence with the Stour the river again reverts to a type more typical of chalk river.
Due to its diversity and near natural structure the Moors River system has been designated as a Site of Special Scientific Interest (SSSI). The SSSI includes a range of habitats within the floodplain of the river as well as the river itself. The citation produced by Natural England for the SSSI (Natural England 1999) provides the main source of information concerning the Moors River system.
As mentioned in the introduction, landowner access was not possible for large sections of the tributaries the Mannington Brook and the Uddens Water. From the short sections of both tributaries that were surveyed, the Mannington Brook appeared to be largely semi natural, flowing over a clay catchment with a diverse pool and riffle sequence. In comparison, the Uddens Water was heavily silt laden due to the acid heathland that it drains. It has been heavily modified for flood defence reasons prior to its confluence with the Moors River, but supported a more natural form with pools and riffles further upstream. 3.2 Geology and Soils
The upper course of the River Crane rises on the chalk of the South Wessex Downs, on the outcrop of Cranborne Chase. Below Holwell the river flows onto tertiary deposits and the chalk becomes more confined. The River Crane becomes a perennial chalk stream fed by streams below Cranborne. Below the chalk the river runs through an area of Reading beds and London Clay before entering an area of sands, gravels and clays near to Verwood. Around this area the river is joined by a number of tributaries that drain acidic heathland and conifer plantation. Here the stream changes from a chalk stream to a slow flowing, low gradient watercourse and the river becomes the Moors River. Near Hurn, the river becomes faster flowing once again, and resembles a gravelly chalk stream (information from the citation for the Moors River System SSSI; Natural England, 1999). 3.3 Geomorphology
The Moors River System is unusual in that it exhibits two distinct river types within a relatively short distance, the characters of which are quite distinct. The upper section of the river system, known as the River Crane, begins life as a winterbourne and then exhibits features typical of a River Type III - Chalk rivers and other base-rich, base flow dominated rivers. In the River Crane, flows are dominated by glides with numerous riffles flowing over clean gravels with the occasional deeper pool. The channel is shallower and flow more lively than the sluggish Moors River.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 40
By contrast, the lower part of the Moors River system, conforms to a River Type I (lowland low gradient river). This river type has a low gradient catchment and river channels running over clay or alluvium (sometimes chalk). Stream power is somewhat variable but is generally low. Under conditions of low anthropogenic impact, bed materials are likely to be dominated by silts and sands, with coarser gravels accumulating at riffles to an extent dependent on upstream sources of coarse substrate and the stream power generated by the catchment. Flow patterns are likely to be dominated by glide, with coarser substrates underlying occasional riffles and finer materials underlying deeper pools. Occasional woody debris log jams would be expected to generate stretches of ponded water, to an extent depending on exact gradient, providing additional and important habitat variability as well as woody debris for decomposer species.
Following the walkover survey it is considered that both sections of the Moors River System exhibit the geomorphology that would be expected for their river types, but the River Crane exhibited greater accumulations of silt and fine sediment than would be expected under solely natural conditions. Restoration will, therefore, need to consider the management of adjacent farmland.
Physical modifications have affected both sections. However, the modifications only impact discrete sections of the river. In addition, it was noted that shade cast by riparian trees was, in places, restricting the establishment of riparian vegetation. Therefore, there is a need for the restoration plans to consider the management of riparian habitat. When considered as a whole, the Moors River system is an essentially natural unmodified river.
Table 6 presents a series of photographs highlighting the key differences between the two river types.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 41
Table 6 Characteristic geomorphology of Type III and I River Types
River Crane (River Type III) Moors River (River Type I)
Intially a seasonally dry winterbourne Slower smooth deep glide flows, abundant coarse woody debris
Extensive aquatic and riparian
vegetation in open, light-rich areas Channel sinuous, frequent meanders
Frequent ox bows in flood plain Frequent shallow riffles and gravel exposures
Extensive shallow glides rich in gravels Extensive deposits of fine silt as side and vegetation bars
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 42
3.4 Catchment land use
The Moors River system is set within a catchment supporting a variety of land uses. The land immediately adjacent to the river is largely semi-natural, with extensive areas of wet alder carr, marshy grassland and fen vegetation. In a number of locations, particularly in the upper reaches of the river, arable farmland is in close proximity to the river which can have an effect on water quality through agricultural runoff and diffuse pollution. The wider catchment includes improved agricultural grazing land together with conifer plantation and lowland heathland. The diversity of the surrounding land use is reflected in the diversity of the river system. 3.5 Habitats and species
The SSSI citation for the Moors River SSSI (Natural England, 1999) provides detailed information on the river system, which is summarised below.
‘The habitat character along the Moors River system has been extensively altered through time with the conversion to agricultural land, but there is a more widespread presence of semi- natural wetland habitats within the floodplain than on many small lowland rivers. Wetland habitat includes areas of swamp, tall herb-fen and fen woodland; this often occurs in a mosaic with wet rush pasture, and partially improved semi-natural grassland.
The River Crane is dominated by typical assemblages of chalk stream plants; however, this is unusual in the prevalence of bank edge trees such as alder which create important features of root and brash tangles. Wooded areas provide diverse banks containing species such as yellow iris (Iris pseudacorus), sedge (Carex) species and opposite-leaved golden-saxifrage (Chryosplenium oppositifolium). More open areas are characterised by purple loosestrife (Lythrum salicaria) and branched bur-reed (Sparganium erectum). Aquatic vegetation is largely brook water-crowfoot.
Further downstream the vegetation changes to resemble a lowland mixed geology community. Broad leaved pond weed (Pontamogeton natans) and unbranched bur-reed (Sparganium emersum) being common in the channel. After the confluence with the Uddens Water the alkalinity drops and downstream the community changes to become more species-rich than that present on the River Crane, including plants such as yellow water-lily (Nuphar lutea) and shining pondweed (Potamogeton lucens). Near Hurn, the chalk stream plants return but in combination with most plants found in the lowland, mixed geology community, creating very diverse river vegetation. The number of aquatic and wetland plant species is among the highest recorded from any section of lowland river in England, and is very exceptional for the relatively small size of the river channel.
Habitat adjoining the river includes fen containing sedge species and common reed (Phragmites australis) as well as many other species; however, the exact assemblage varies depending on localised conditions. Lower down these are replaced by tall herb-fen communities dominated by reed canary-grass (Phalaris arundinacea). On the floodplain, communities are more species- rich, with swards of meadowsweet (Filipendula ulmaria), marsh valerian (Valeriana dioica) and common meadow-rue (Thalictrum flavum).
Riparian alder trees are again a prominent feature of the river, although die-back is noted to be a significant problem on parts of the system. In addition, areas of fen woodland, dominated by alder and willow species, have developed along the river, with understory plants such as water avens (Geum rivale) and various sedges. In other areas fen meadow has been allowed to develop where the ground is not well drained and is managed by light grazing or hay cutting. These areas often contain sharp flowered rush (Juncus acutiforus) and purple moor grass (Molinia caerulea), in addition to yellow iris.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 43
The Moors River system has a very high dragonfly fauna, with records of 32 species including some now extinct form Britain. Some sites within the river are also particularly rich in other invertebrate fauna, supporting over 100 species including groups of caddisflies, mayflies, beetles and snails. Nationally scarce species such as the whirligig beetle (Gyrinus urinator) have also been recorded within the river.
Breeding bird assemblages are typical for small chalk rivers, and include water edge species such as grey wagtail (Motacilla cinerea) and kingfisher (Alcedo atthis). In other areas little grebe (Tachybaptus ruficollis) have been recorded. A variety of warblers and reed buntings (Emberiza schoeniclus) have also been recorded where suitable habitat is present. The lower reaches support wintering common snipe (Gallinago gallinago) and teal (Anas crecca).
Otter (Lutra lutra) have been recorded breeding on the river in the past, and this species is now known to have re-established itself after being absent for some time. Both water vole (Arvicola amphibius) and water shrew (Neomys fodiens) have been recorded on the river, especially in the upper reaches in the River Crane’.
During the course of the field survey numerous wintering teal were disturbed from the ponded areas and ox bows present along the Moors River, whilst numerous woodcock (Scolopax rusticola) were flushed from riparian wet woodland. 3.5.1 Non Native Invasive Species
The Environment Agency highlighted that non-native invasive species are becoming an issue of conservation concern on the Moors River system. These include the American signal crayfish (Pacifastacus leniusculus) and plant species such as Himalayan balsam (Impatiens glandulifera).
It is outside the scope of this document to predict the potential effects of non-native species on native flora and flora, but it is an issue that the broad ecological vision will need to address in the long term. For example, fencing out livestock from the river bank to encourage marginal vegetation may encourage the spread of non-native invasive plant species. It is understood that the Dorset Wildlife Trust has recently begun a project investigating the issue of non-native invasive species on the Moors River System. The results from this project should feed into the long term ecological vision for the Moors River System. 3.5.2 Alder die-back
It has been highlighted (Pers Comm. Doug Kite, Natural England) that alder disease caused by the fungus (Phytophthora albi) is a problem on some sections of the Moors River system. For example, downstream of Moors Valley Country Park to the confluence with the Stour, there is almost complete loss in some lengths, as well as along the Uddens Water. It is recommended that replacement of any loss of alders should be through the planting of Phytophthora resistant alder varieties or, if appropriate, additional native species of local provenance which are not susceptible to alder disease.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 44
3.5.3 Current ecological Condition of the Moors River System
The Moors River SSSI is made up of a number of management units of various habitat types, 10 of which relate to Rivers and Streams habitat types. The condition assessment for these 10 units records the condition of the river as either unfavourable no change, or unfavourable declining. The main reasons for the unfavourable condition are listed (amongst others) as being:
. inappropriate scrub control . inappropriate weirs, dams and other structures . water pollution - agriculture/runoff . water pollution and discharge It is outside the scope of this report to undertake a detailed review of the conservation objectives and the reasons for the Moors River system being in ‘unfavourable’ condition. However, Natural England (Pers. Comm Doug Kite) highlighted a number of key points pertinent to the ecological visions, which are summarised below:
Siltation The SSSI Condition Assessment (Natural England, 2009) indicates that the upper section of the Moors River system is subject to a high frequency of silt and sand deposition, ranging from 40- 50%, which is well above the conservation objective (less than 10% silt cover and more than 50% clean cobbles, pebble and gravels on the river bed). Due to the high levels of siltation the upper Moors River System is recorded as not being in favourable condition. The geomorphology database, created following the walkover field survey, indicates potential sources of siltation being stock poaching and erosion of banks, although only a discrete amount of active bank erosion was noted during the course of the field survey. Surrounding land use outside of the immediate riparian zone, including heathland and arable farmland, are also potential sources of diffuse pollution.
Channel Form In a number of sections (4 out of the 10 SSSI management units) of the Moors River system the river is reported to not be in favourable condition due to physical modification to the channel form, and the effects of previous activities such as weed cutting.
In-stream barriers There is a barrier to fish migration in the lower section of the Moors River System just before the confluence with the Lower Stour at the Hurn Gauging Station. A fish pass has been fitted but this weir may still pose a barrier to the upstream movement of coarse fish species and eels. A study of the obstructions to fish migration, focusing on migratory salmon and sea trout, on the Moors River System upstream of the confluence with the Uddens Water has been undertaken (Solomon, 1998). This study identified 15 structures that could potentially affect migrating fish. Two structures at Verwood Trout Lake Upper Sluice (located in SSSI management unit 4) are considered to be a significant barrier to the upstream movement of fish. Two further structures, Holwell Lower Mill Sluice and Holwell Higher Mill Sluice, are considered to be a barrier on some flows. Due to these barriers to migrating fish the Moors River SSSI is reported to not be in favourable condition, and this is reflected in the fact that impacted fish communities are cited as one of the reasons for the Stour catchment as a whole failing to achieve good status under the WFD. The citation for the Moors River System is presented in Appendix 1.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 45
3.6 Water Quality and resources
A review of the Environment Agency website (http://maps.environment-agency.gov.uk) indicates that the Moors River was in the top two grades for biological and chemical water quality. Despite this, sections of the Moors River system are in unfavourable condition due to its water quality. Therefore, restoration measures that reduce the input of pollutants, particularly diffuse pollution, will be required (see Section 3.9.1). 3.7 Landscape and recreation
The Moors River system is set within a fairly narrow floodplain with extensive areas of wet woodland, fen and marshy grassland adjacent to the river. Outwith the immediate floodplain are large areas of conifer forest and heathland developed on sands and gravels. In the top portion of the catchment the River Crane flows through a narrow chalk valley but, again, extensive wet woodland and grassland lie adjacent to the river.
Recreation is not as developed on the Moors River system as on the Middle and Lower Stour, and it is considered that increased access may result in damage to some of the sensitive wetland habitats and associated species present. The Moors Valley Country Park, situated at the point where the river loses its chalk stream character and becomes the Moors River proper, is an extremely well-used public amenity and the adjacent land use comprises areas of amenity grassland (for example the golf course and playing fields) as well as semi-natural areas. Fishing is carried out along parts of the river but is relatively low key. 3.8 Fisheries
The river system supports a limited diversity of fish species. Coarse species such as chub, gudgeon, pike and, most abundantly, dace dominate the lower Moors River. The River Crane, however, is dominated by brown trout, the chalk stream providing some of the principle spawning habitat within the Stour catchment. This is a natural population and comprises a high proportion of sea trout. Also, within the River Crane bullheads, a species of European concern, eel and brook lamprey occur extensively within the headwaters of the river.
The gauging weir at Hurn, and a number of other minor hatch structures, are likely to pose a barrier to the movement of fish species. Overall, the Moors River System is considered to maintain healthy coarse and brown trout fisheries. 3.9 Physical Modifications 3.9.1 Intensive agriculture and diffuse pollution
Although not a physical modification of the river channel, in some locations the land adjacent to the Moors River system supports agriculturally improved fields used for stock grazing or arable crops, although for the most part the immediate riparian farmland is managed relatively extensively. Intensive agriculture can result in high levels of nutrients and diffuse pollution entering the river and encourage dense beds of nettles and other ruderal weed species in the riparian zone.
Diffuse pollution is recognised as a problem in the upper catchment such that it is a priority catchment under Defra’s Catchment Sensitive Farming Programme.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 46
3.9.2 Weed cutting and channel maintenance
Until the 1980’s weed cutting in the channel took place to increase drainage and flow conveyance. In addition, overhanging tree cover and marginal vegetation was cut back to accommodate the weed cutting boat. The river is still dynamically adjusting to this past management regime with some sections becoming narrower and gravel shoals beginning to develop. Weed cutting occurred mainly in the lower section of the river system from near Bournemouth Airport to Woolsbridge. 3.9.3 Provision of water for mills, small lakes and to enable watercress production
In a number of locations water from the river has been used to supply lakes mainly constructed for fishing purposes, mills and, in one instance, a watercress farm. These abstractions tend to consist of a small weir or sluice which diverts water into a side channel. In some instances the channel of the main river may have been straightened for a short distance (Figure 15).
Figure 15 (A) Weir/sluice structure on the River Crane at Verwood trout farm and (B) short section of straightened channel. A B
3.9.4 Channel realignment and over-widening and deepening
As indicated above, in a small number of locations the channel of the main river has been realigned either to aid the provision of water to a lake or mill, to improve agricultural drainage or for flood defence purposes. In some instances this has been combined with dredging to create a uniform channel with trapezoidal banks to aid the conveyance of flood water and land drainage; in most instances the length of channel affected is relatively discrete (Figure 16).
Figure 16 (A) Section of the Moors River straightened for agricultural drainage compared to (B) a typical sinuous section of the main river A B
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 47
3.9.5 Flood Alleviation
Within the Moors Valley Country Park there are two large lakes, Moors Lake and Crane Lake, which were constructed in 1985 and 1989 respectively. Both are off-line lakes with level control structures that divert flow into the lakes during periods of high river flow, which is released slowly as levels in the river drop. The construction of both lakes and channel realignment diverts water at times of high flow.
Figure 17 (A) Brick Flume that regulates flow, (B) river inlet to Moors Lake A B
3.9.6 Intensification of adjacent land-use
For the majority of its length the land adjacent to the Moors River system consists of semi- natural wet woodland and wet grassland habitat that is either neglected or used for low intensity stock grazing. In a number of locations the grazing is more intensive and the fields have been subject to agricultural improvement. In addition, there are two golf courses, Moor Valley Country Park and Crane Valley, where the management of the grassland extends right up to the edge of the river bank and can include bank protection measures. In these locations the riparian vegetation can be less diverse and extensive compared with other locations on the river.
Figure 18 (A) Golf course grassland management and bank protection at Crane Valley Golf Course and (B) intensive grazing adjacent to the Moors River A B
3.9.7 Barriers to fish migration
As mentioned above, there are a number of structures on the Moors River system that could constitute a barrier to the upstream migration of migratory fish, including the gauging weir at Hurn and various sluices and other structures further upstream, for example the hatches at Verwood Trout farm.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 48
3.9.8 Summary of physical modifications and ecological consequences
In summary, the Moors River System is an essentially natural river system exhibiting an exceptionally diverse range of aquatic and wetland vegetation. On a local scale the river has, in the past, been modified to provide water for mills, fishing lakes and for watercress cultivation. In the southern reaches of the river, below Verwood, discrete lengths have been improved and realigned for agriculture, urban drainage and flood protection. Despite the historical management of the river, the channel is essentially natural in form and structure
This section discusses the broad ecological consequences of the physical modifications to the river that have been identified. It should be noted that the physical modifications can potentially have both negative and positive impacts on the ecological status of the river, particularly at the local scale. Table 7 identifies the physical modifications identified and their broad ecological consequences associated with them.
Table 7 Physical modifications and ecological consequences Physical Ecological consequences Modification
Historical river De-shoaling and weed cutting removing in-channel habitat, management creating uniform channel.
Tree cutting and scrub removal causing loss of bankside vegetation and supply of shade and in river woody habitat.
Provision of water Weirs and sluices can act as a barrier to fish migration. for mills, small lakes and water- Leads to slowing of flows and upstream ponding of water cress production and reduction of in-channel diversity, leading to a lack of physical features such as side and point bars that are required by some species of flora and fauna.
Causes fine silt sediment to be deposited over gravels and other coarse bed sediments reducing suitability of gravels for fish spawning.
Reduction in flow rates prevents the scouring of gravels which become covered in fine sediment sediments reducing suitability of gravels for fish spawning.
Channel Leads to reduction of in-channel diversity realignment Over-wide channels lead to a lack of narrow fast flows which would scour and keep spawning gravels clean. Lack of fast flows restricts the distribution of water crowfoots that require riffle conditions.
Causes fine silt sediment to be deposited over gravels and other coarse bed sediments reducing suitability for spawning fish.
Deep water prevents the establishment of in-channel emergent vegetation and transitional marginal wetland
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 49
Physical Ecological consequences Modification
plants.
Often associated with bank protection which limits the generation of sediment, eroding banks etc.
Flood alleviation Disconnects the floodplain from the channel, inhibiting the establishment of transitional wetland habitats.
Can be associated with channel over-deepening and realignment
Intensification Reduces connectivity of river with floodplain habitats adjacent land use Reduced diversity and extent of riparian vegetation
Can lead to poaching and increase in diffuse sediment smothering vegetation and spawning gravels.
Fertilizers and herbicides can enter the river promoting algal blooms and reducing aquatic plant diversity.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 50
3.10 Long term ecological vision for the Moors River System
The following section sets out the long-term, ecologically based vision for the Moors River system. This is necessarily high level; encompassing the entire Moors River System. However, specific examples have been used to exemplify the extensive natural potential that can be drawn upon. In order to fully reflect the diversity of the Moors River system the ecological vision has been split to cover the chalk stream elements (the Type III river) and the lowland low gradient elements (The Type I river.) 3.10.1 How the ecological vision was produced
To develop an ecological vision it is necessary to identify the natural condition and range of ecological features such conditions should support. Given the presence of natural or near natural sections, it is possible to identify what the Moors River system should look like, if it were entirely natural, and what characteristic ecology it should support. However, in the following discussion it is important to note that changes to the physical structure of the river will not necessarily alter the impact of other factors, in particular poor water quality, on the river‘s ecology.
Table 8 summarises the target natural geomorphological features and associated characteristic ecology that would be expected for the river types present in the absence of any physical modifications, based on the generic descriptions for river types produced by Natural England (Mainstone 2007) and observations made during the field survey.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 51
Table 8 Typical Geomorphology and Ecological characteristics that could be expected for the Moors River System River Type Summary of typical Geomorphology Summary of characteristic ecology Summary of restoration requirements
River Type I Under conditions of low anthropogenic impact, bed River bed gravels or other coarse substrate provide an In stream gravels present but river subject to diffuse pollution Lowland Low materials are likely to be dominated by silts and essential but generally scant habitat for a wide variety of impacts. Restoration should ensure all adjacent farmland gradient rivers sands, with coarser gravels accumulating at riffles to invertebrate and fish species in these river types, including entered into the Defra Catchment Sensitive Farming an extent dependent on upstream sources of coarse caddis-flies, riffle-beetles and mayflies, and a diverse fish Programme. substrate and the stream power generated by the assemblage such as dace, bullheads, stone- loach (Barbatula catchment. barbatula), brook lamprey (Lampetra planeri), minnow (Phoxinus phoxinus) barbel, salmoid species and stickleback In some discrete locations the channel has been realigned so Flow patterns are likely to be dominated by glide, with (Gasterosteus aculeatus). restoration should focus on introduction of large woody debris coarser substrates underlying occasional riffles and to diversity flow regime and encourage the creation of sinuosity finer materials underlying deeper pools. On those sections naturally supporting a sufficient extent of in the channel. Occasional logjams would be expected to generate gravels, brown trout and some stonefly species of the Leuctridae stretches of ponded water, to an extent depending on and Nemouridae families (which are more tolerant of silty exact gradient, providing additional and important substrates than other stoneflies) would characteristically occur. habitat variability as well as woody debris for Gravels and swifter flows also provide rooting opportunities for decomposer species. species such as water-crowfoot (Ranunculus penicillatus subsp. pseudofluitans) and water-milfoil (Myriophyllum spicatum), with an Considerable meandering can be expected in these attendant fauna. types depending on natural sediment supply and hydraulic energy, generating sequences of alternating In general, in physical terms, the diversity of the in-stream fauna of steep and shallow bank profiles which may lead to rivers in these types will be largely dependent on the extent to Diverse marginal vegetation is present but its extent is limited vertical cliffs (in less cohesive sediments) and point which the naturally occurring coarser substrates have been by shade cast by riparian trees. Restoration aims to manage bars respectively. retained, and maintained in good condition (i.e. without excessive riparian trees to create a mixture of shade and sunlit patches to siltation). In quieter sections and backwaters with finer substrates, benefit the establishment of riparian vegetation. a flora and fauna more associated with stillwaters develops, including unionid mussels and pea-mussels, Libellulid dragonflies, agrionid damselflies, burrowing mayflies, water-snails, alderflies, and various families of caddis-fly (such as the Limnephilidae). The insect fauna is heavily dependent on an active marginal and wetland fringe of vegetation for hatching, resting, feeding and mating, and as a flow refuge under spate conditions.
Fish species may include perch, roach and eel, with chub, barbell, trout salmon and gudgeon where flows are stronger. Remove potential barriers to movement of fish in the river channel. On shallow banksides (particularly the insides of meander bends), a significant zone of hydrological transition can be expected, with beds of emergent species such as branched bur-reed (Sparganium erectum) and reed canary grass (Phalaris arundinacea), and wetland species such as brook-lime (Veronica beccabunga), water forget-me-not (Myosotis scorpioides), water-mint (Mentha aquatica) and water-cress (Rorippa nasturtium-aquatica). Vertical cliffs provide nesting opportunities for kingfisher and sand martins (Riparia riparia), as well as for burrowing bees and wasps and a range of other insects specialising in bare soils. Water-voles thrive in bank sides of intermediate slopes with tall herb vegetation and an active marginal zone of emergent plants.
Riparian trees provide an important additional habitat dimension, generating submerged exposed root systems that provide in- Management of riparian trees to promote a mosaic of shade channel habitat for fish and and sunlit patches, together with discrete localised planting to invertebrates, potential holt and resting sites for otters, a source of maintain long term continuity of this habitat. woody debris and leaf litter for the river, and varying within-channel light and temperature regimes that add further habitat diversity.
Riparian scrub provides additional important habitat for otter and bird species such as warblers and reed bunting. The co- occurrence of wooded and open river margins has been shown to be important for a range of invertebrate species in chalk streams,
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 52
River Type Summary of typical Geomorphology Summary of characteristic ecology Summary of restoration requirements
and there is no reason to suspect these species act any differently in other river types. Regular diurnal movements between the two habitats have been observed by a range of dipteran flies, caddis- flies and mayflies.
On the wider floodplain, natural flooding regimes can be expected to give rise to inundation wetland, particularly alongside rivers with low base-flow, and fen and carr vegetation, particularly alongside high base-flow rivers. River Type III - This river type characteristically has low hydraulic The shallow cross-sectional profile and low scouring energy of Chalk rivers and energy. Under natural circumstances, such rivers the river type gives rise to an abundant plant community, including Removal of weirs and hatches that slow flows and cause impoundment of water. other base-rich, would have formed indistinct multiple channels in-channel specialists such as the running through carr and fen habitat. In downstream water-crowfoots and starworts and highly active marginal base flow sections, channel definition is likely to have vegetation including watercress, and water forget-me-nots. A dominated increased, with multiple channels meandering across mosaic of beds of submerged plants and gravels is typically rivers. the floodplain. created, with enhanced scouring between the plant beds generating gravels low in silt content. The Chalk Rivers Handbook (Natural England and Environment Agency 1999) describes pragmatic Marginal vegetation characteristically encroaches into the channel reference conditions (low anthropogenic impact) for as flows recede from spring through summer, thereby reducing Ensure continued reduction of in-channel maintenance to allow chalk river catchments as low- intensity land use, effective channel width and maintaining current velocities in the vegetation to remain in the channel. meadow dominated, with a high water table and main channel. Over the winter this vegetation is scoured out and frequent winter inundation of riparian and floodplain the process begins again in the spring. areas. The majority of the river network of this type can be expected to have distinct channels, low The invertebrate fauna is particularly abundant under conditions of longitudinal frequency of riffles and pools (high low anthropogenic impact, owing to the refugia provided by Restoration of straight uniform sections by the introduction of occurrence of glide habitat), extensive gravel extensive gravel substrate and abundant in- channel and marginal large woody debris to promote the diversity of flows that these substrates, infrequent gravel shoals and exposed vegetation. Mayfly, caddisfly and gastropod mollusc species are species require. riverine substrates, shallow cross-sections, a sinuous particularly dominant, with some species adapted to the channel form, and common occurrence of riparian gravel substrate and others to submerged plants. Species shifts fen. are evident from the upper to lower reaches of the river type, according to reductions in current velocity and progressive fining of Remaining lengths of indistinct channel running bed substrates. For example, Gammarus in the gravels and through fen and carr should be cherished as Simulid (black-fly larvae) in the Ranunculus beds of the faster-
examples of the truly natural expression of the river flowing upper reaches both giving way to Brachycentrid caddis-flies
type, and re-created where feasible/appropriate. in the more sluggish lower reaches. Such transitions are evident at
Features such as gravel shoals and riffles are all the a smaller scale in relation to the sequencing of riffles and pools
more important for their limited occurrence. within a given river reach, relating to the alternating conditions of
higher velocity/coarser substrates and lower velocities/finer
Chalk rivers generally have a highly biologically active substrates.
hyporheic zone in their unimpacted state, with considerable hydrological and biological connectivity The characteristic fish community also shows a longitudinal transition dependent largely on current velocity and substrate between the lower and upper layers of the gravel bed Removal of barriers to the movement of fish species. of the river, as well as strong lateral connectivity into types. Salmonids dominate the upper and middle reaches, making using of the cleaner gravels for spawning and early growth. riparian areas. Downstream salmonids give way to rheophilic
cyprinids such as dace and chub, which also make use of gravels
for spawning but at reduced incubation depths. Patchy submerged
plant cover is essential for the fish community as refuge and
feeding habitat.
Finer substrates are important to a range of species in this river Remove weirs and other structures that cause ponding of flows type, including lampreys. Under conditions of low anthropogenic and allow deposition of fine substrates to accumulate in the impact, silt beds accumulate behind natural structures (such as upper, faster flowing reaches of the river. long-jams) and are present at higher levels in gravel substrates than in other river types. Finer substrates become more dominant in lower reaches, with gravels eventually becoming restricted to occasional riffles.
Winterbournes, the ephemeral headwaters of the river type, The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 53
River Type Summary of typical Geomorphology Summary of characteristic ecology Summary of restoration requirements
constitute a distinctive habitat hosting many specialist plant and animal species adapted to resisting the dry period. The dry period can vary from a few months to most of the year, and the length of Management of riparian trees to promote a mosaic of shade and this period determines the precise composition of the winterbourne sunlit patches together with discrete localised planting to flora and fauna. Riparian trees are a vital habitat component, maintain long term continuity of this habitat. generating submerged exposed root systems that provide in- channel habitat for fish and invertebrates (such as white clawed Crayfish)potential holt and resting sites for otters ,a source of woody debris and leaf litter for the river, and varying within- channel light and temperature regimes that add further habitat diversity. Riparian scrub provides additional important habitat for otter and bird species such as warblers and reed bunting.
The co-occurrence of wooded and open river margins has been shown to be important for a range of invertebrate species in chalk streams. Regular diurnal movements between the two habitats have been observed by a range of dipteran flies, caddis- flies and mayflies. Both lightly grazed and un-grazed open margins are ecologically important – shorter, lightly poached swards favour smaller perennial flowers and invertebrates of bare ground, whilst taller swards are vital for emerging insects as hardening-off‘ areas and for general refuge.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 54
In order to address the issues identified in relation to physical modifications on the river, and restore the river to its target natural condition, a range of restoration measures will need to be implemented. The restoration approach is summarised in the section below 3.10.2 Restoration approach for the Moors River
The following outlines the recommended approach to restore, as far as possible, the natural physical processes to the river. The emphasis is on encouraging assisted natural recovery rather than significant engineering works. The restoration measures proposed should be considered against the Conservation Objectives for the Moors River SSSI.. The restoration approach has been divided into the following broad categories:
. Adaptive management (involves the modification of existing land management practices to promote the development of habitat conditions beneficial to the flora and fauna characteristic of the river) . Physical rehabilitation (involves physical intervention, often using machinery, to restore channel features to a more natural state following historical degradation) . Managing Control Structures (involves the management of structures that control water levels in the river) Further detail on these approaches is presented below. 3.10.3 Adaptive management
. Allow vegetation within the river channel and riparian bank vegetation to develop naturally with a minimum management intervention. Low intensity management such as coppicing and pollarding of riparian trees in densely wooded reaches to encourage a greater diversity of vegetation may be appropriate. . Where banks are trapezoidal in section allow stock grazing to break down the banks and diversify the bank habitat, creating marginal zones for the establishment of riparian flora. In addition, continue to support low intensity grazing of riverside habitats where this is appropriate.. . Maintain near natural stretches (the majority of the river) in favourable, or near favourable, physical condition, allowing continued change in channel planform and cross section in response to active processes. . Promote measures to reduce the intensity of agricultural and other land management types (such as country parks and golf courses) on land immediately adjacent to the river and encourage the creation of wide buffers of riparian vegetation. 3.10.4 Physical rehabilitation
Where reaches have been straightened to promote drainage and exhibit little in channel diversity undertake restoration by:
. Increasing the quantity of locally derived coarse woody debris within the channel (in those sections where coarse woody debris is lacking) either as log jams or, if more appropriate, individual pieces of large woody debris by felling and coppicing riparian trees and fixing to the bed and banks of the river. This will promote localised scour and sediment deposition, encouraging habitat diversity and promoting the establishment of a more diverse channel. . Consider a limited programme of riparian tree planting (where appropriate on those sections of river with largely open banks and a dearth of riparian trees) to increase the The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 55
supply of natural sources of coarse woody debris and increase the extent of exposed bank side tree roots which offer refuges for a variety of aquatic flora and fauna. However, it should be noted that the continued maintenance of open reaches with a diverse in- channel and riparian vegetation is an important ecological feature of the river complementing the more wooded reaches. Replace loss of alders (consider disease resistant alders in addition to other native species of local provenance not susceptible to alder disease), and where river vegetation is low diversity and uniform use tree shade and woody debris to diversify habitat conditions. 3.10.5 Managing control structures
. Allow to degrade, remove completely, or remove sections of weirs and hatches/sluices where there are no/limited cultural heritage/flood protection constraints, and allow natural processes (both upstream and downstream) to re- assert their influence. Downstream weirs to be removed first where possible, to allow channel to adjust and enable the effective management of flood risk consequences (if any). Such works should be carried out at an appropriate time of year to minimise ecological disturbance and comply with current best practice. . Partial removal or lowering of weirs/sluices may reduce these impacts whilst providing the same benefits. Where this is not possible, fish passes and eel ladders should be incorporated into the structure. 3.10.6 Aims and Objectives of the Ecological Vision
The aims and objectives of the ecological vision are set out in Table 9. Figures 19 and 20, provide a graphical interpretation of the ecological vision for the river, using specific reaches to exemplify the existing conditions and what restoration measures would be required. The left hand side of the figures shows examples of the river in a near natural state, including the geomorphological features to be expected, whilst the right hand side shows the impacts of physical modifications and the potential ecological benefits of restoration. Separate illustrations have been produced for the River Crane and the Moors River.
The tributaries of the Moors River System, the Mannington Brook and the Uddens Water, have not been mentioned specifically in the ecological vision, as it was felt that the aims and objectives of the ecological vision were sufficiently encompassing. However, detailed restoration options for each reach of the tributaries have been set out in the reach by reach restoration plans which have been produced in association with this ecological vision.
Finally, section 3.11 describes a sustainable, more naturally functioning Moors River System from the perspective of someone walking along the river highlighting the physical features and associated wildlife that they could expect to experience. This is designed to give a feel for what the Moors River System could look like once substantial restoration works have been implemented and the ecological vision largely realised.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 56
Table 9 Aims of the ecological vision for the Moors River System
Dynamic
Moors River System
Geomorphologically active and capable of creating its own energy and diversity, with swift flows increasing the quantity of clean gravels free of fine sediment, and other coarse sediments, creating alluvial bars. Fine sediment will continue to be represented in the channel but deposited in areas of slower flow.
A channel with the freedom to change its planform (as far as possible given flood defence concerns and critical infrastructure) and cross section in response to active geomorphological processes.
The location and nature of individual geomorphological features will be dynamic; however, each reach will show representative examples of typical features which would be expected given the site-specific conditions and the characteristic river type. Limited restrictions to the migration of species along the channel (at both low and high flows), through weir removal or, if not practicable, provision of suitable bypass channels. Where immovable constraints exist the channel planform and cross section will be representative of natural processes within the limits of these constraints
In good ecological condition Naturally functioning and self-sustaining river system that exhibits a full range of characteristic habitats and species.
Sufficient extent of each habitat/species population to enable the ecology to adapt in response to the dynamics of the channel.
Limited restrictions to the migration of species along the channel (at both low and high flows), through weir removal or, if not practicable, provision of suitable bypass channels.
The channel of the upper part of the river system will be relatively narrow, sinuous and often with shallow sloping banks, with numerous in channel features. Flows will be dominated by shallow smooth glides interspersed with swifter water flowing over clean gravels causing riffled flows; there will be occasional deeper pools. Riparian alder trees and mixed trees and scrub vegetation will continue to be a feature of the river with coarse woody debris creating extensive side bars rich with emergent vegetation. Woody sections will be interspersed with open habitats such as grassland and fen vegetation.
The channel of the lower part of the river system itself will be highly sinuous with regular meanders with numerous in-channel features. Flows will be relatively sluggish overall with numerous deep pools, but with discrete sections of faster flow. Riparian alder and willow trees will be a significant feature of the river, with trees collapsing into the river causing natural slowing and ponding of water flows. Abundant coarse woody debris will cause flow to be diverted and trap silt and other sediment creating wide side bars.
Along the river system the shade cast by riparian trees will not dominate and there will be large stretches where abundant light levels will allow extensive growth of both aquatic and emergent vegetation that will, during the summer, smother the channel from view.
The immediate floodplain will continue to support an extensive and diverse range of semi-natural habitats including alder carr, marshy grassland, fen and species-rich meadows.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 57
Ideally there will be back channels and side channels increasing the area of available habitat but these may not carry much flow and become dry seasonally during periods of little rainfall.
Hydrologically and Ecologically Connected to the floodplain
Restoration of floodplain connectivity through: Removal of floodbanks or encourage their erosion and loss by river movement. Establishment of floodplain woodland in areas of extensive poor habitat quality, especially where this will assist flood risk management Diversification of the floodplain land surface to create a more uneven surface with drier and wetter areas, especially in areas of poor habitat quality where past spoil spreading and levelling has reduced floodplain connectivity. Allowing the re-establishment of the natural floodplain hydrology, typically with wetter seepage fed land at the edge of the floodplain and drier silt raised land towards the river, by appropriate management and removal of floodplain drainage.
The river and adjacent floodplain should be regarded as a single intimately linked feature with the river levels being linked to a high water table in the adjacent floodplain. The river should continue to maintain good hydrological and physical connectivity between its floodplain to enable the river to function, enhancing floodplain habitats, in particular marshy grassland, fen and wet woodland (carr).
The adjacent floodplain should continue to support an extensive and diverse range of semi-natural habitats including alder carr, marshy grassland, fen and species-rich meadows.
Resilient to the effects of climate change.
Extent and diversity of habitats and species and their connectivity along the entire channel sufficient to allow adaptation to change.
Set within a cultural heritage and landscaping setting
Retains features of significant heritage value within the river and floodplain setting, such that there is an appreciation of past and present land uses.
The natural form and dynamics of the channel complemented by low intensity adjacent land use, particularly low intensity agriculture, with grazing of wetland habitats where appropriate. Where adjacent land use is intensive (e.g. golf courses and country park) ensure that a suitable riparian buffer is maintained to prevent adverse effects on the river system.
Manage public access so that sensitive habitats are not compromised and use high profile ‘hotspots’ such as the Moors Valley Country Park to highlight the ecological importance and sensitivity of the Moors River System and the adjacent habitats in the surrounding floodplain. Ensure that fishing interests reflect the near natural features of the river channel and are centred on maintaining the native wild stocks of trout and coarse fish
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 58
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 59
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 60
3.11 Description of the Moors system once the ecological vision is implemented
The following section presents an idealised description of the restored river walking downstream along the Moors River System. This has been set out to provide a description of how the river may differ as a result of the proposed restoration measures.
At first the river is a winterbourne, dry for large parts of the year or with flow being merely a trickle.
Below Cranborne the river is relatively narrow and shallow, with a lively and vigorous flow and occasional deep pools. There are numerous shallow sections with extensive gravel deposits and features such as side bars or other in-channel features that reduce the width of the channel creating localised areas of faster flow that scour the gravels keeping them free of silt. In many sections there is abundant light reaching the river and diverse aquatic and marginal vegetation.
There are extensive areas of aquatic and riparian vegetation that, in the summer, may blur the distinction between river and dry land and partly hide the channel from view. Large alder and willow trees are frequent along the river bank, some of which have collapsed into the river. The tree branches and roots collect fine sediment, creating large accumulations on which species-rich emergent vegetation is established. These silt deposits divert flow, creating areas of marginal dead water close to the bank where fish fry can shelter, and faster flows in mid-channel suitable for trout.
There are extensive areas of wet riparian woodland adjacent to the river which are wet underfoot and have been left to develop naturally. Large tree roots create suitable conditions for otters to rest and lie up; a good example is the woodland upstream of Pinnocks Moor Bridge.
In other locations, the channel is more open, with good light levels and diverse wet grassland and fen adjacent to the river. These areas are wet and difficult to walk through. Cattle may graze these areas during the summer months and the extensive riparian vegetation provides foraging habitat for water voles. There is excellent connectivity between the river and the adjacent wetland habitats.
Passing through Crane Valley Golf Course it is noticeable that the ‘rough’ includes a wide margin adjacent to the river in contrast to the bright green swards of the playing greens. Moving downstream and entering the Moors Valley Country Park, the flows become slower, with more frequent glides and deep pools, and tight regular meanders are beginning to be present. Despite the public access the river here has wide vegetated margins. Coarse woody debris has The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 61
been pegged in to the banks to alter the flow regime in straight channel sections and information boards are used to highlight the importance of the river and surrounding habitats.
Moving downstream, the agricultural intensity in the floodplain becomes more obvious. The river is mostly unfenced but, in places, temporary seasonal fencing is set back from the bank top so that a wide buffer strip of riparian vegetation has established. Wet woodland and grassland is still frequent along the margins of the river. Grazing stock have access the river margins on a seasonal basis to graze and break up tall vegetation and diversify the bank profile through light poaching. A dramatic change will be noted when the silt laden Uddens Water enters the main river; flows slow and extensive silt berms become a more obvious feature of the river.
In the vicinity of Bournemouth airport the river scene is almost primeval. The river is relatively deep, slow flowing and with frequent meanders. Large alder and willow trees line the banks, with branches and whole trees collapsing in to the river creating log jams and slowing flows. Wetland features such as ditches and old ox bows are abundant and progress on foot beside the channel is difficult due to the wet conditions. There are frequent open areas to the floodplain, lightly grazed by cattle with a diverse emergent and riparian plant community. Finally, just before the confluence with the River Stour, flows increase again and shallow riffles with clean gravel exposures begin to reappear.
Weirs and sluices that used to impound flow and pose a barrier to migrating fish have all but been removed.
Public access to the river for informal recreation, such as walking and fishing, is good but is focused on ‘honey pot’ sites such as the Moors County Park. Access elsewhere is encouraged but is not to the extent that it results in detrimental impacts to the sensitive wetland habitats located adjacent to the river. 3.12 Conclusions from the ecological vision
The aims and objectives of the ecological vision are designed to be relatively firm and inform the reach by reach restoration action plan, which will a flexible working document. The core restoration actions for the Moors River System will include:
. Removal of weirs and other structures to remove barriers to fish passage and restore a diverse flow regime to the river. . Where sections have been straightened install large woody debris to promote diversity of flow conditions to start the process of developing a more sinuous channel. . Use stock grazing to break down trapezoidal banks creating marginal zones for wetland flora to establish. . Manage riparian woodland and trees to create a mosaic of sunlit patches and shade for the benefit of riparian vegetation and invertebrates. . Ensure the adjacent catchment is entered into the Catchment Sensitive Farming Programme to reduce the quantify of diffuse pollution entering the system.
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 62
4 References
The following section list the references and other sources of information used in the production of this report.
The Water Framework Directive (more formally the Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy).
The Eels (England and Wales) Regulations 2009. Statutory Instrument 2009 No.3344 (available at http://www.legislation.gov.uk/uksi/2009/3344/made)
Environment Agency March, (2010). Eel Management Plans for the United Kingdom. South West River basin District
Sear, D.A., Hill, C.T. & Downes R.H.E (July 2008). Geomorphological assessment of riverine SSSIs for the strategic planning of physical restoration. Natural England Research Report NERR013
Doug Kite (Natural England, 2009). Moors River System SSSI Dorset. Common Standards Monitoring Condition Assessment to 2010.
Natural England (1999). SSSI Citation for the Moors River SSSI JNCC, (2005) Common Standards Monitoring Guidance for Freshwater Fauna Mainstone C. (2007). Rationale for the physical restoration of the SSSI river series in England (Environment Agency, 2009). River Basin Management Plan for the South West River Basin District. River Basin Management Annex B Water Body Status Objectives Environment Agency, (2009). The Dorset Stour Catchment Abstraction Management Strategy Dr. D.J. Solomon (1998). Obstructions to fish migration on the River Crane and Mannington Brook. Report for the Environment Agency Natural England (1999). SSSI Citation for the Moors River SSSI Doug Kite (Natural, England 2009). Moors River System SSSI, Dorset, Common Standards Monitoring Assessment to 2010 Natural England, (2009). Conservation Objectives, for the Moors River System SSSI
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 63
Appendix 1 Moor River SSSI Citation
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 64
The Lower Stour and Moors River —Broad Ecological Vision and Restoration Measures Hyder Consulting (UK) Limited-2212959 Page 65