Our Vision

Introduction

The partnership

about this project

Our vision is that the Windrush catchment is clean and full of wildlife, managed sustainably and valued by all.

WINDRUSH CATCHMENT PLAN 

Working Summary February 2023                                              Available as a PDF

Why this document?

Since the Windrush Catchment Partnership was established progress towards achieving the objectives of our shared vision has been limited. As a partnership much effort was expended on writing a catchment plan. The resulting lengthy document  (link to the Windrush Catchment Plan: Action Plan (windrushcatchment.com) ) while containing much relevant information also looks in need of significant updating and does not set out clear targets. 

The purpose of this document is to update the original catchment plan, to provide a more accessible summary and, above all, to set achievable targets.

The Vision

The Windrush Catchment Partnership (WCP) vision : the Windrush catchment is clean and full of wildlife, managed sustainably and valued by all.

The role of the WCP is to work with partners to facilitate the delivery of the partnership’s vision, not least by identifying the obstacles to, and specifying the actions required for that delivery.

The WCP was set up in 2014. It has been hosted since 2022 by the Cotswolds Rivers Trust.

The Watercourses

The watercourses encompassed within the designated Windrush catchment partnership area are:

l the Windrush originating on Cotswold limestone near Temple Guiting and flowing south-east through Bourton-on-the-Water, Burford and Witney before joining the Thames at Newbridge. Its principal tributaries are the Dikler and Sherborne Brook.  

l the Leach joining the Thames just east of Lechlade. It is spring-fed and winterbourne in its middle reaches.

l the Thames between the Leach at Lechlade and the Evenlode at Cassington is included within the Windrush catchment.  The Great Brook is a distributary of the Thames that sources upstream of Rushey Weir (close to Buckland Marsh) and re-joins the Thames upstream of the Windrush confluence. The Radcot Cut, Sharney Brook and Shill Brook are tributaries of the Great Brook.

Water Quality

Water quality is the reason most frequently assigned by the EA to waterbodies in this catchment as the reason for not achieving good ecological status.

Point source pollution

 Discharges from sewage treatment works have been identified as the major source of point source pollution in the catchment. STWs in the Windrush catchment are largely operated by Thames Water. Principal STWs of concern are the large works at Witney and numerous smaller works including Bourton-on-the-Water, Carterton, Clanfield and Standlake. Discharges of untreated sewage have been widespread and numerous. These have been justified by the operator as “storm discharges” which are consented. However, research by Professor Peter Hammond of WASP (Windrush Against Sewage Pollution) shows that many discharges are in fact “Dry Spills” when rain has not fallen, or “Early Spills” when untreated sewage has been discharged though the works in question is not treating the volume of sewage for which it has been licensed.

A significant number of properties in the catchment are not connected to the waste water treatment network and problems with poor maintenance of septic tanks and privately operated treatment plants remain additional concerns. 

Diffuse pollution

Diffuse pollution in the catchment associated with agricultural practices remains an issue and measures to address concerns include:

l improving soil management by adding organic matter and decreasing compaction capturing rainwater from farm buildings rather than allowing it to wash across farmyards slowing water flow through ditches by adding small bunds (managing sediment transfer through underdrainage)

l growing suitable crops on slopes to prevent the loss of topsoil

l altering tramlines and gateways to prevent soil loss 

l targeting the application of fertilisers

l riparian fencing

l careful management of slurry

l buffer strips

Turbidity

One of the most commented on indicators of ecological degradation of the Windrush has been increased turbidity. First observed in the early 1980s and then confined to the river’s middle reaches

between Bourton and Witney, turbidity has worsened considerably in the past 20 years and affects the whole of the Windrush from Bourton to the Thames. The upper Windrush and its Dikler and Sherborne Brook tributaries have not displayed marked or persistent turbidity.

Increased turbidity is not unique to this catchment and has been observed on other Cotswold rivers.  A number of studies of Windrush turbidity were undertaken in the 1980s and 90s and identified turbidity as related either to the precipitation of homogeneous calcite and/or Lias clay strata in suspension. However, the reasons for why this developed in the 1980s and why it worsened significantly this century have not been proven conclusively.

Natural environment

Parts of the Windrush and Leach and virtually all of the Thames (apart from the Duxford Loop) have been subjected to historic channel modification, including re-sectioning, dredging and straightening, resulting in disconnection from the floodplain, a typically uniform trapezoidal cross-section, a paucity of gravels or natural river bed and a lack of diverse riparian habitat. Some reaches are heavily over-shaded. Although these issues have all had an impact on the ecology of the catchment, it is important to note that very few of them have occurred in the past 35 years, and have thus had little or no impact on recent declines in the Ecological Status of Windrush waterbodies.

Fisheries

The fish populations of the Windrush which were excellent have seen a marked decline in recent years. Spring spawning flow sensitive species like grayling and barbel are worst affected.  Both species are intra-gravel spawners, with the most likely cause of their decline being anthropogenic nutrient enrichment. This results in poor intra-gravel water quality during their spring spawning period. Changes in land use and discharges from sewage treatment works are the most likely sources of this enrichment

The Windrush’s main tributaries, the River Dikler and the Sherborne Brook both support strong and self-sustaining wild brown trout populations. 

The River Leach also holds a robust self-sustaining population of wild brown trout. Coarse fish are largely absent due to the number of barriers which prevent upstream movement from the River Thames.

Invertebrates

The Windrush and its tributaries generally possess some stretches of stony streambeds and diverse flow types with a strong base-flow constituent, providing locally good quality habitat for macroinvertebrates. However, there are also reaches that have been significantly damaged by past dredging, reducing overall habitat quality.

Excellent invertebrate communities have historically been found throughout the catchment, with sites recording BMWP scores in excess of 200. However, there are clear indications of a long term decline in invertebrate populations. A decline in upwing (Ephemerid) fly specieshas been noted throughout much of England. Recent riverfly monitoring by volunteers has also indicated a reduction in invertebrate diversity and abundance, particularly in the reaches between Burford and the River Thames.

Also of particular interest are the two known extant populations of white-clawed crayfish, possibly the last populations of this species remaining in the Thames river basin. The populations are at Swin Brook (waterbody 30440 ) near Burford), and the Hazelford and Coombe Brook (waterbody 30450) near Taynton. These populations should be protected to prevent loss as a result of disease or colonisation by non-native crayfish.

It is also acknowledged that non-native invasive signal crayfish have a detrimental impact on slow moving invertebrates, leading to local extirpations of some species.

Macrophytes

Data for macrophytes from historic surveys noted that species present were generally typical of a small, silted, enriched (semi-eutrophic) base rich chalk stream. Over time, various surveys have recorded a decline in the abundance and distribution of water crowfoot and opposite-leaved pondweed. Survey results suggest that increasing nutrient rich sediment deposition is increasingly limiting the in-stream vegetation in the upper Windrush. Between Sherborne and Burford, submerged vegetation was (in 1978-1996) dominated by spiked water milfoil, with the river dominated by plant species indicative of semi-eutrophic conditions. From Burford to Witney surveys reported strong stands of water crowfoot with several species of pondweed, common starwort, spiked milfoil and yellow water lily. Between Witney and the River Thames, water crowfoot dominated the in-stream vegetation, appearing in large stands where habitat was suitable, with stands of perfoliate, fennel and horned pondweeds also present.

More recently (2000-present), there has been a very clear decline in the abundance of all species of submerged macrophytes in the reach between Burford and Witney, with an almost complete absence of these species in some sections of the river since at least 2016.

None of the WFD waterbodies have achieved ‘High’ status for the plant communities, and only 2 out of the 12 waterbodies with survey data are classified as ‘Good’. Most are ‘Moderate’ indicating that they are damaged to some extent by the presence of phosphate in the water leading to the overgrowth of certain species and a lower diversity.

It should be noted that the campaign group ‘Windrush Against Sewage Pollution’ disputes the EA’s survey data and classifications for both macrophytes and invertebrates, having gathered evidence which suggests significant negative changes at most monitoring points.

Birds

The area has been highlighted for its importance for breeding waders, in particular lapwing, redshank, snipe and curlew. These four species continue to decline, with redshank and snipe having been almost completely lost from the area as breeding species. Causes of decline are thought to include loss of or changes to management of habitat, drainage of wet grassland, predation of nests and chicks and disturbance. Designated an Environmentally Sensitive Area in 1994, Natural England, aims to work with partners and farmers to halt the decline of curlew, a species of international importance.

Invasive Non-Native Species

Non-native American signal crayfish are very abundant within the Windrush and pose a high risk to the white-clawed crayfish and slow moving invertebrates.

There are some areas where non-native plant species are present in high abundance leading to the exclusion of native plants. Himalayan balsam is common on the lower Windrush and Thames where in places it dominates the bank side vegetation; Australian swamp stonecrop (Crassula) is found growing on the bed of the channel in the Sherborne Brook.

Impacts of mineral extraction

The Lower Windrush Valley has been transformed by quarrying into a patchwork of some 60 lakes. In the 1990s the Environment Agency reported breaches of planning permission at one or more now closed quarries where the operator had dug too close to the river and hadn’t sealed the excavated face with clay. This resulted in a reduction in river flow with loss of water from the channel to the adjoining lake. In response to this the Environment Agency commissioned consultants WS Atkins to investigate the causes of reduced river flow in the Windrush catchment. Atkins reported in 1999 and identified that quarry dewatering, along with a range of other factors, may contribute to a loss of flow on the eastern arm of the Windrush

A follow up to the Atkins study published by the Environment Agency in 2005 identified the need for further study with a combination of potential contributory factors, including loss from the river to the surrounding gravels  and subsequent evaporation from restored gravel pit lakes, reduced winter rainfall, and altered flows in distributaries. However, the EA decided against further investigation.

Flooding

Flooding is a major issue – with many direct and indirect impacts on people, property, businesses including farming, and the environment. There are already many flood-sensitive areas, towns and villages in the catchment including Witney, Standlake and Bampton. 

An increased interest in more natural solutions to flooding has led to schemes by catchment partners that are exemplars of Natural Flood Management (NFM) and there is a strong case for much such schemes within the Windrush catchment. With increasing signs of climate change making weather patterns less predictable, storms can be stronger and more frequent, with flood peaks exceeding ‘normal’ levels. 

Low flows

Low flows, as experienced in 2022, can have negative consequences for water quality and overall biodiversity, including concentration of pollutants and nutrients, algal blooms, and increased exposed bank habitat availability for invasive species such as Himalayan Balsalm. There is the increasing possibility of more frequent and more prolonged periods of low flow due to climate change. 

The damaging impact on river flows of prolonged periods of lower rainfall may be compounded by groundwater and surface water abstractions. The principal public water supply abstraction in the Windrush Catchment area is Thames Water’s abstraction from the Thames at Farmoor. There are other public water supply abstractions within the catchment area and numerous small private licensed abstractions.

Development pressures

The Windrush catchment area has experienced and is experiencing considerable development pressure and change with rapid expansion of the towns and villages within the catchment.  This has impacted on watercourses in a number of ways.  Development may result in loss of permeability increased surface water run-off, the straightening and/or culverting of small streams and disturbance and erosion from increased activity/recreational use. However, the greatest impact has arisen from increased pressure on sewage treatment works (STWS). Campaign groups have highlighted that the lack of capacity of many STWs to treat current volumes of sewage and infiltrating surface water have led to hugely increased pollution.

Ameliorative measures to tackle some of the negative impacts of development include a requirement to demonstrate biodiversity net gain (BNG) and the use of Sustainable Urban Drainage Systems (SUDS).  So far, any positive benefit from such measures has been limited and has not offset the negative environmental impact of development within the catchment.

Navigation on the Thames

A significant physical modification issue within the catchment is the substantive historical channel

alterations and ongoing water level controls and management primarily focussed on allowing for

navigation by vessels along the Thames section of the Windrush catchment (from Lechlade to

Eynsham). The requirement to maintain powered navigation, while increasing recreational value and usage, has greatly limited any proposed efforts towards restoration to a more natural state of river. However, by pass channels to improve fish passage and a more sensitive approach to channel de-silting and riparian maintenance offer the potential for significant mitigation.

Catchment Action Plan

The key issues

Water quality

Water quality is the key issue in this catchment. There is now ample documentation showing the deterioration of the River Windrush from a clear calcareous river, rich in fish, invertebrate and plant life to its current turbid and impoverished state. Other water courses in the catchment such as the Shill Brook display similar environmental damage. Phosphorus and nitrogen enrichment are identified as the primary causes of environmental degradation.

Water quantity

In comparison with many catchments in SE England the Windrush catchment is not heavily abstracted. However, abstraction is an issue as there are damaging licensed abstractions in operation as well as licensed abstractions which though currently inactive might be re-commenced. There is a large public water supply abstraction at Farmoor which is environmentally damaging, though the damage it inflicts falls outside this catchment. There are numerous small licensed abstractions; cumulatively, these may impact negatively at times of low flows.

Habitat

The riverine habitat along the rivers and streams of the catchment is of variable quality. Much of the middle Windrush has been severely damaged by past dredging and removal of the river’s gravel bed.  The lower Windrush has also been severely impacted by mineral abstraction. Other watercourses like the Great Brook have been dredged and straightened. Opportunities for habitat improvement are numerous throughout the catchment.

Development

Ensuring that development is sustainable is a continuing challenge in this catchment. Delivering adequate sewage treatment capacity, sustainable drinking water supply, SUDs and Biodiversity Net Gain (BNG) must be pre-requisites for future development and improvements must be back-dated to ameliorate for past development.

Flood defence

In an era of anticipated climate change characterised by more frequent extreme weather events, improving flood defences and flood resilience must be a high priority. In the past flood defence and environmental protection have often been seen as conflicting. Fortunately, this is no longer the case with a recognition that natural flood management (NFM), by attenuating flood peaks, is both a cheap and effective way of reducing flood damage and is environmentally enhancing.

Progress so far

Progress to date has primarily take the form of a number of habitat projects, sometimes involving more than one partner. The following are some examples.

Recent and current projects

Cotswold Rivers Living Landscape – Gloucestershire Wildlife Trust working to restore, recreate and reconnect wildlife-rich spaces in the rural and urban areas of the upper Windrush catchment by working in partnership with volunteers, local communities, landowners, schools and businesses to restore/reconnect wetland habitat, promote catchment sensitive farming techniques and implement NFM schemes.

The Lower Windrush Valley Project worked with the Environment Agency to roll out the Yellow Fish scheme in Witney, West Oxfordshire. The focus area was an industrial estate surrounding Emma’s Dike, a tributary of the River Windrush, where there have been several pollution incidents in the past. 

The scheme aims to make people aware of possible pollution pathways by raising awareness about sources of pollution and how to prevent incidents taking place. Yellow fish stickers were placed near surface water drains leading directly to watercourses.

Habitat restoration at the Windrush/Sherborne Brook confluence – Cotswold Flyfishers

Cotswold Flyfishers(CFF) have an on-going programme of habitat improvement work on the Cotswold rivers. One projects has been to improve fish passage between the River Windrush and its tributary the Sherborne Brook. CFF were particularly keen to open up fish passage as the water quality of the Sherborne Brook suggested it would be a more productive spawning site for many species, but particularly grayling which have been in serious decline in the catchment.

The Windrush Project

The Windrush Project has developed out of extensive discussions between Thames Water, WASP and the CRT. All parties agree that sewage pollution is a major issue in the catchment and that the water quality of the Windrush is poor.  TW take the view that sewage pollution is not the only reason for poor water quality and want parallel action on diffuse pollution, sewage mis-connections and habitat issues, coupled with community engagement, and have agreed to fund a project under the auspices of CRT that will deliver this. CRT and WASP have expressed a willingness to embrace this process provided that there is real action from TW to end sewage pollution of the Windrush and the resulting nutrient enrichment which is destroying the river.

Setting SMART targets

For Water quality

Reducing point source pollution.

Thames Water have committed to reducing storm discharges by 80% by 2030. Whilst the WCP wants to see storm discharges (ie discharges of untreated sewage) reduced to zero and soon, we welcome the commitment from Thames Water and await the confirmation that the Windrush catchment will be designated “sensitive” .

A reduction in storm discharges, however welcome, will be insufficient to ensure that stw effluents meet good water quality standards. We would urge the EA to review permitted standards for all stws within the catchment. “Dry spills” and “Early spills” are illegal and should not happen. When they do happen the WCP expects the EA to take enforcement action. We should not wait for 2030 for this.

The WCP is very conscious that while phosphorus removal from effluent at both large and small works has been adopted in some catchments this hasn’t been extended to the Windrush catchment. We think phosphorus removal from effluent discharged from Bourton-on-the-Water stw is a priority if the Windrush is to achieve good ecological status within a reasonable time frame. We suggest that 2027 should be the target date for P removal at Bourton.

Point- source pollution from septic tanks and small private treatment works must also be addressed. We think it is reasonable to expect that by 2026 the Windrush Project will have identified the vast majority of small facilities of concern in the catchment. 

Surface water ingress into the foul sewer network is one of the reasons behind repeated storm discharges (“dry spills”).  Reducing infiltration is a priority and the WCP calls for a “twin-track” approach to this. On the one hand re-lining of sewers by TW to prevent infiltration is essential. At the same time we expect that by 2027 the Windrush project in conjunction with local councils and other organizations will have identified rainwater-sewerage mis-connections which require action from the appropriate authorities. 

Reducing diffuse pollution

We think that by 2030 diffuse pollution from agriculture can be substantially reduced by the adoption of a number of measures.  These include wider riparian buffer strips, broadleaved tree planting on exposed slopes and stock fencing. An excellent mechanism for achieving this will be the extension of the farming clusters which have already been a success story in the NE Cotswolds.

For sustainable abstraction

Within the catchment there are good examples of sustainable abstraction. Supply of drinking water to Witney from Farmoor is an obvious example: surface water is abstracted downstream of consumption. Groundwater abstractions in the Cotswolds are generally examples of an unsatisfactory environmental model.

Ensuring wider adoption of sustainable abstraction practices is almost certainly an objective that the WCP cannot achieve through partnership working. This does not mean nothing can be achieved and we call for a review of ground-water abstractions within the Windrush catchment.

For improving Habitat

The primary focus of partners in the WCP to date has been the improvement of habitat and that is because, providing funding can be secured, is probably the easiest to achieve. We think the target for the future should be more ambitious projects involving a several partners in each project and that these should be integrated with flood defence projects, especially NFM. We would hope to see WCP partners engaged in a number of such projects by 2026.

For managing and regulating Development

We regard it as essential that development delivers biodiversity net gain. We think it a fair summary to say that to date the regulation of such development has typically delivered pollution and environmental degradation. The WCP calls upon LPAs to refuse development permission if it is unclear that there is sufficient additional sewage treatment capacity to serve the development. The WCP similarly requires that it is mandatory for all developments to provide SUDs. We think 2025 is a reasonable target for achieving this.

For Flood defence

Reducing flood risk requires a multi-track approach. The priority is, of course, to prevent homes and businesses flooding. The flooding of agricultural land within the flood plain, far from being preventable, is an integral part of flood defence. However, mitigation is possible and can work to everyone’s benefit. The adoption of NFM schemes in the headwaters will mitigate flood peaks. So will the adoption of SUDs. If rainwater from patios and other hard surfaces are directed to soak aways flood peaks will be attenuated. Roads and gateways are major transmission routes for surface water run-off. We hope that an extension of the work of the Windrush project or similar project (perhaps as a product of TW’s Smarter Water Catchments) will lead to the identification of such damaging flood transmission routes. In conjunction with our farming clusters we would hope that delivery of flood and soil traps in gateways could be widespread by 2030.

Richard Knowles 7.2.23

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