■ v THE RIVER AVON AND ITS TRIBUTARIES NEAR MALMESBURY Towards a Solution En v ir o n m e n t A g e n c y » BRISTOL** u f t f f t T r n June 1997 Towards, a Solution b a c k g r o u n d

The River Avon and its tributaries near Wessex Water and Bristol Water accept that Malmesbury have been the subject of their groundwater abstractions in the detailed investigation since 1990. catchment are having an adverse impact Consultants, WS Atkins, were appointed in on river flows. Both companies are working 1991 to determine the impact of closely with the Environment Agency to abstraction and other management effect early improvements to river flows by practices on river flows, river biology and implementing a combination of measures fisheries. WS Atkins used the MIKE-SHE involving increasing stream support and computer model to represent the drainage changing abstraction arrangements. processes in the catchment and to assess Following the recommendations in the the impact of abstraction. Atkins study all parties have agreed that the trials should be implemented on a The study concluded that abstraction by staged basis, starting with those measures

Tetbury Avon, downstream St Leonard's Wessex Water and Bristol Water that may provide an immediate benefit. Bridge significantly reduce river flows throughout the catchment. Both the Sherston and In August 1995 Wessex Water increased The study area includes the Tetbury tributaries suffer a loss of flow due the output from their stream support upper reaches of the River to river bed leakage caused by depressed boreholes at Luckington, Stanbridge and Avon above Great Somerford groundwater levels in the Great Oolite Tetbury. The month long trial showed that gauging station. The two main aquifer around the abstraction boreholes considerably more water could be obtained tributaries, the Sherston and near Malmesbury. Although the Great from the Inferior Oolite aquifer and that Tetbury Avon, meet at Oolite is overlain by clay-like deposits to most of the water added as stream support Malmesbury. These and a the south and east and separated from the remained in the river down at least as far as number of other minor underlying Inferior Oolite by Fullers Earth Great Somerford. Bristol Water voluntarily tributaries are fed by surface these clays are not total barriers to water reduced their average summer abstraction runoff and by springs from the movement. Geological investigations have for public water supply at Shipton Moyne Great Oolite aquifer. Wessex shown that near Malmesbury the clays are and Long Newnton thereby leaving more Water abstract from the Great thin and the Great Oolite aquifer is close to water in the Inferior Oolite aquifer for Oolite for public water supply. the surface. During the winter when water stream support. Bristol Water's supplies mostly levels in the aquifer are high, water flows come from the Inferior Oolite. from the Great Oolite into the river. As Further trials in 1996 were designed to see Wessex Water also abstract water levels in the aquifer drop during the if the benefits observed in 1995 could be from the Inferior Oolite aquifer summer the flow reverses and leakage sustained over a longer period. The and pump the water directly takes place from the river to the aquifer. prescribed flows at Fosseway and into the river for stream Brokenborough gauging stations that support. KEY determine when water should be pumped into the river for stream support were - - Surface Catchment ---- increased. Wessex Water used its stream Outcrop Boundary (CO) support boreholes to maintain new target □ Town CATCHMENT MAP ✓ I flows set by the Environment Agency and Flow Metering Stations SIMPLIFIED Bristol Water continued to abstract at • Stream Support Boreholes reduced rates. 1 Water Supply Boreholes • Bristol Water Co. The results of these and other work aujy • Wessex Water PLC conducted during 1996 are summarised in • N this leaflet. The leaflet also contains an I X Long NewMon ^ m ^ N — % outline of work to be undertaken in 1997 [_Brokenborough C h a rity Shipton and and the issues that need resolving / Backbridge V before full and lasting remedies can be Fosseway lalmes finalised. These remedies will be finalised by the year 2005 at the latest. Sherston Avon Bridge Rodbourne

Luckington Hullavington * 1 Ml/d =0.22 Mg/d =0.0116 m3'* Lower ! Q uintin

Cover photo: Sherston Avon at Silk Mills, September 1996.

I ____ ■ Inset photo: August 1995, prior to stream support trial ^ S H S f a o m

5 15 25 DISTANCE - km from origin CO GREAT OOLITE FE FULLERS EARTH 10 INFERIOR OOLITE FM, CB & OC FOREST MARBLE, CORNBRASH & OXFORD CLAY Stream Support Trials

Prescribed Flows

To compensate for the reduction in river 8 Ml/d. Depending on the weather this As part of the trial the Agency has flows due to abstraction for public water year these measures may lead to several developed two new target flows to help supply Wessex Water are required under weeks more stream support than would be protect the lower reaches of the Sherston the terms of its licence to pump water normal under the license conditions. Flows Avon and Tetbury Avon in Malmesbury. into the river from its stream support at the gauging stations will be used to The target flows are located in Malmesbury boreholes. The licence stipulates that trigger stream support. Once support has at St Johns Bridge (Sherston Avon) and pumping should start when flows at the begun the support boreholes will be used Back Bridge (Tetbury Avon). During the gauging stations at Fosseway, to try to maintain target flows in summer of 1996 output from the stream Brokenborough or Great Somerford fall Malmesbury and the existing prescribed support boreholes was not limited to 2.5 below prescribed levels. flow (28 Ml/d) at Great Somerford. Ml/d but allowed to increase to maintain the following targets: In 1995, as a trial, the prescribed flow at Fosseway gauging station was increased Target Flows St John's Bridge (Sherston Avon) 7.2 Ml/d from the licensed value of 8 Ml/d to Back Bridge (Tetbury Avon) 6.8 Ml/d 12MI/d. In 1996 the prescribed flow at Malmesbury Fosseway was increased again, this time to The licence limits output from each of the The targets are based on the results of a 14 Ml/d . This increase led to stream support stream support boreholes at Luckington, river diary exercise completed by local being introduced two to three weeks earlier Stanbridge and Tetbury to 2.5 Ml/d. people in 1992 and 1993 and are designed than normal on the Sherston Avon. Pumping at 2.5 Ml/d has generally not to protect the important amenity value of Although the prescribed flow at been sufficient to maintain flows at the the rivers in Malmesbury. The target flows Brokenborough was increased from 6 Ml/d gauging stations at prescribed levels, or were generally met or exceeded, the main to 8 Ml/d in 1996, stream support was prevent the flows in Malmesbury receding exception being due to a pump failure in actually turned on before flows at to very low levels. mid August. Because of rainfall flows were Brokenborough reached 8 Ml/d. Support generally well above target levels. Stream therefore started about four to five weeks In August 1995, for example, prior to the support continued at Luckington, earlier than required under licence start of the stream support trials flow in the Stanbridge and Tetbury until water levels conditions. Sherston Avon at Silk Mills was reduced to increased in the Inferior Oolite in the a trickle (see photo insert on the cover). autumn. In 1997 stream support on the Sherston Now, as part of the trial, Wessex Water are Avon will be started when flows at able to add a total of 24MI/d from the Fosseway gauging station fall below 14 M three stream support boreholes instead of I/d and on the Tetbury Avon when flows at the 7.5MI/d specified on the existing Brokenborough gauging station fall below licence. ENVIRONMENT AGENCY

0 7 9 6 9 0 Towards, a Solution FLOW AT BACKBRIDGE 1996

|UNE |ULY AUGUST SEPTEMBER OCTOBER NOVEMBER AT ST JOHNS BRIDGE 1996

Ml/d

JUNE |ULY SEPTEMBER OCTOBER NOVEMBER

MEASURED FLOW TARGET FLOW

During the trials the Environment Agency, will also be monitoring groundwater levels Wessex Water and Bristol Water have been around their stream support boreholes. actively seeking the views of the public Information on the quantities abstracted about the benefits observed. The for stream support, groundwater levels and Stream support, Luckington Malmesbury Liaison Croup has been river flows will be publicised by the Agency formed to provide a direct link between during the trial. the Agency, the water companies and residents and organisations who have an interest in the river. In general the Great Somerford feedback that we have received has been very positive. Most people considered that In addition to maintaining target flows in flows through Malmesbury were Malmesbury in 1996 the prescribed flow of maintained at an acceptable level in 1996. 28 Ml/d at Great Somerford was exceeded We will therefore again try and maintain for most of the summer. Whilst flows at flows, at, or above these targets in 1997. Great Somerford benefited from the Stream support will start at a relatively low increase in stream support to meet the rate (2.5 Ml/d) but gradually increase as targets in Malmesbury there is still concern, river flows decline during the summer. particularly amongst anglers, that flows there remain too low. The Agency will be regularly monitoring river flows and groundwater levels The Agency is reviewing the prescribed throughout the trial and liaising closely flow at Great Somerford and will identify with both water companies. Wessex Water what changes are necessary to create acceptable in-river conditions. As an integral part of this work the Agency has Actual flow at Great Somerford and flow if the licence engaged the Institute of Freshwater conditions had been followed, 1996 Ecology (IFE) to undertake an angling survey on the river. IFE have already conducted a preliminary investigation which has indicated that it is possible to quantify the relationship between angling conditions and flow. The main study, which starts in 1997, is designed to objectively Ml/d assess the potential benefits of changes in the flow regime on wet and dry fly angling conditions for trout. The results will be used to help in assessing an environmentally acceptable flow at Great Somerford. The eventual target flow is Actual Flow Flow under licenced conditions Prescribed flow likely to reflect a reasonable balance between water use and the environment. JULY AUGUST SEPTEMBER OCTOBER NOVEMBER o ENVIRONMENT AGENCY - SOUTH WEST REGION

Standard Distribution List for New Publications

Regional Management Team Regional Advisory Panel Katharine Bryan Dennis Mitchell Martin Booth Roger Willis Bill Grigg Chris Rothwell Nick Gupta Gerald Manning David Horwood Karen Morgan Paul Jones Geoff Bateman Regional/Area Staff Geoff Boyd Richard Horrocks Howard Davidson Terry Newman Chris Birks Stuart Bray Dave Pilkington Devon AMT Ian White Carole Steer Nigel Morris Malcolm Chudley John Hescott Jim Constantine Richard Symonds Heather Barker Brian Frankling Nigel Reader Bob Collett Malcolm Newton Steve Woods Anne Riley Jeanette Collett Anil Koshti Customer Service Centres Cornwall AMT Penny Amraoui Gill Shrimpton Sue Young Brian Sinkins Charissa Day Gordon Trapmore Tracey Speare Dean Evans Martin Williams PR Contacts David Sheriff Margaret Buckhurst (Library) x Sheila Turner 2 copies Bridget West (Bristol) x 2 North Wessex AMT copies Gwynneth O'Rourke Emer O'Connell ISSUED BY: Ian Legge Miles Wilson JENNY GRIFFITHS Ken Tatem Public Relations Rob Turvey PR Managers Roger Merry Laura Oliphant - Anglian Officer Robin Callender Jean Harper - Thames Andy Gardiner Geoff Champion - Welsh Date: Steve Chandler Carol Parker - North West Jackie Spicer-Bert - Midlands For further copies South Wessex AMT Jean Varley - North East Rosemary Stone Liz Cook - Southern please contact PR on Bob Huggins Extn 2279 Chris Bray Publication Officers Helen Toft Lesley Woolnough - Anglian Graham Lightfoot Paul Dykes - Thames Ron Curtis Lara Dalton - NE Geoff Hardwicke Liz Sanz - NW Valerie Albrighton - Mids Christine Russell - Welsh Committee Services Lorraine Dempster - South. Peter Sadgrove Cumulative Output from all Inferior Oolite Stream Support Sources

River Avon at Great Somerford Impact on Inferior Oolite • Impact on Great Oolite groundwater water levels groundwater water levels

The water for stream support is abstracted There was no evidence of lowering of considering the possibility of pumping from the Inferior Oolite aquifer. The water levels in the Great Oolite as a result from the peripheral boreholes rather than combined cumulative output from Inferior of pumping from the Inferior Oolite. the main collecting well. No problems are Oolite stream support sources at Indeed, as was seen in 1995, water levels in anticipated at Long Newnton where the Luckington, Stanbridge and Tetbury in the Great Oolite boreholes downstream of pump sets have been renewed and lowered. 1996 was similar to that in 1990. In 1996 the stream support discharge increased the Luckington and Tetbury boreholes were when the rate of stream support increased, Other Sources pumped well into the Autumn, even when probably due to recharge of the Great Thirty-nine privately owned boreholes and river flows had risen well above target Oolite aquifer from the river. springs have been identified which might levels. In 1990 output at each source was be affected by increased pumping for constrained to 2.5 Ml/d by licence stream support. During the summer water conditions but, due to the very dry Impact on Other abstractions levels were measured in twenty five. Three weather, flows were below prescribed levels private supplies in the Inferior Oolite are for much of the year. Bristol Water believed to be vulnerable to low water Bristol Water's public water supply source levels. In all three cases there may be scope Because there were no dramatic changes in at Tetbury is less than 2 km from Wessex to lower the pump further down the output from the stream support boreholes Water's stream support borehole. Both borehole. in 1996, the quantities pumped only abstractions are from the Inferior Oolite. increased slowly, the effect of abstraction Abstraction for stream support in 1996 There are four private wells in the Great on water levels in the Inferior Oolite aquifer reduced water levels in the public water Oolite which are currently experiencing is difficult to determine, other than at the supply borehole. If the level had fallen low water levels. The trials so far have stream support boreholes themselves. another 5 to 10 metres then Bristol Water indicated that increased pumping from the However, the 1995 test indicated that the would have difficulty maintaining sufficient Inferior Oolite aquifer does not have any abstraction does effect the water level in output to meet public water supply impact on levels in the Great Oolite. It the Inferior Oolite over a wide area. demand in the local area. This winter therefore follows that increased pumping Bristol Water have installed a new larger from the Inferior Oolite is not likely to be The rain in October and early in November pump at a lower level in the existing hole. the cause of present or future supply did not significantly reduce the seasonal problems in the Great Oolite. However, decline in water levels in the Inferior Oolite. Because 1996 was not especially dry and Wessex Water will continue to monitor This suggests that the connection between Bristol Water reduced their abstraction the these wells and many other boreholes in the Inferior Oolite and the Great Oolite is fall in water levels at their public water the Great Oolite until the extent and poor and therefore that the opportunities supply abstractions at Long Newnton and nature of the link between the two aquifers for recharge are limited. What is not clear Shipton Moyne did not present a problem. is confirmed. from the field trial is whether after a dry However, in a drier year abstraction for winter the Inferior Oolite aquifer will public water supplies coupled with higher recharge sufficiently to maintain the target levels of abstraction for stream support flows, without adversely impacting other might lead to a problem at Shipton licensed abstractors. In 1997 the Agency Moyne. If water levels fall to the height of will use its MIKE SHE groundwater model the adits, 46 metres below the ground to explore this issue. surface, then abstraction for public water supply could be interrupted as sediment at the base of the adits is swept into the main collecting well. Bristol Water are Changes to Abstraction a c t i o n ■ Arrangements Bristol Water Last summer Bristol Water temporarily significant reduction in leakage from the reduced abstraction from its boreholes at Sherston Avon between Fosseway and Shipton Moyne and Long Newnton to 9 St John's Bridge which almost certainly Ml/d. Prior to 1995 abstraction frequently helped make it possible to maintain the ranged between 14 Ml/d to 18 Ml/d. By target flow at St John's Bridge with reducing its abstraction Bristol Water left relatively moderate rates of stream support. more water in the Inferior Oolite for However, as the changes are relatively Wessex Water to use for stream support. small it is difficult to determine the overall Water from Bristol's Purton Water benefit accurately. Wessex Water will repeat Treatment works, which is supplied by the the trial in 1997 and the Agency will River Severn, was used to make up the continue to monitor groundwater levels shortfall. Bristol Water will continue to and river flows in the area. abstract at a reduced rate in 1997. The Agency will use its groundwater model to assess whether target flows can be Daniels Well maintained without further changes to Leakage abstraction arrangements at Shipton Moyne and Long Newnton. I In the past the very low flows on the Wessex Water Sherston Avon in Malmesbury have been WS Atkins suggested that Wessex Water's exacerbated by leakage near Daniels Well. Cowbridge abstraction may have more During 1995 a series of temporary repairs impact on the river than any other source. using sand bags and clay were carried out. To test this theory more rigorously Wessex These significantly reduced the losses in Water agreed to stop using Cowbridge for this area and led to a marked improvement an extended period last summer and to in flows through Malmesbury. make up the lost output from their Milbourne and Charlton sources. In the In 1996 a number of minor leaks in the event not all the lost output could be clay seal that appeared over the winter switched to the others sources due to the were repaired. Although gaugings in the limitations of the existing infrastructure and river and the leat indicate that the sand individual source licences. Nevertheless, the bags and clay are effective, river water is test, which started on 12 August and still being lost along the stretch from continued until 24 October, confirmed the Riversdale to St John's Bridge. During the theory that Cowbridge does have a low flow period in 1996 about 32% of the significant impact on the river. Shutting flow measured at Riversdale was being lost. down Cowbridge led to a marked increase In absolute terms losses averaged in water level in nearby Great Oolite approximately 4.7 Ml/d. boreholes. There also appeared to be a During 1997-98 the Agency intends to develop plans for a more permanent restoration of the river bank and leat at Daniel's Well. All relevant parties will be fully consulted. If the preferred solution is acceptable it will be implemented, but not before 1998. In the meantime the Agency will continue to maintain the clay and sand bag system to ensure leakage at Daniel's Well is kept to a minimum. In addition the Agency will consider whether it is possible to reduce leakage elsewhere along the Riversdale to St John's Bridge stretch.

Daniels Well leat after sealing with sand bags and clay Habitat Towards, Improvements a Solution

The Malmesbury Avon and its tributaries The consultants concluded that most of the have been subjected to a wide range of lower cost remedies such as changes to degrading influences over recent decades stream support could be justified without that have reduced both the asthetic and including the benefit associated with 'non environmental quality of the river. In use' ( the amount people who do not use addition to trialing measures designed to the river are willing to pay to resolve the improve flows the Agency and Wessex low flow problem). Water are also funding a number of other initiatives in the catchment that will lead to local improvements in the river Next environment. At Silk Mills on the Sherston Steps Avon, for example, Wessex Water have cut I notches in the weir and installed gabion planting baskets on each step of the weir. A number of important issues require These baskets have been planted with resolution before a final remedy is yellow flag and water lilies to improve the recommended. The Agency needs to visual amenity of the river as it passes develop its review of an environmentally through the town. acceptablc flow at Great Somerford. The sustainability of the new stream support Downstream of Malmesbury, fisheries and abstraction arrangements also need to consultants have worked with local river be tested using the Agency's MIKE SHE bank owners, fishing leaseholders and groundwater model. In particular the Agency staff to improve the river Agency must be confident that increased environment by cleaning spawning gravel, pumping for stream support will not building weirs and groynes and managing adversely impact any other legitimate bank side vegetation. The pools and gravel water interests. riffles that have been created have been shown to hold much higher numbers of At this stage there is promise that the coarse fish than adjacent areas. prefered solution may be based, at least in part, on the increased stream support and Following an electro-fishing survey on the altered abstraction arrangements described Sherston last year that showed that the in this document. The Agency will develop Habitat improvements downstream of Malmesbury distrubution of wild brown to be extremely a fully costed business case to support patchy a number of options for habitat these or additional proposed changes and improvements have been identified. Where consult with all interested parties before appropriate these will be implemented in submitting proposals to OFWAT (The Office 1997. The value of the habitat of Water Services) for inclusion within the improvements will be monitored by third periodic review (AMP3). If OFWAT do electro-fishing. not approve the inclusion of this scheme in the water companies Strategic Plans the Agency will continue to look for other Assessment of possible sources of funding. Whatever the Potential Costs and outcome of the AMP3 submission the Environment Agency, Wessex Water and Benefits to the Bristol Water agree that full and lasting Environment remedies shall be finalised by 2005 at the latest.

The Agency accepts that should it be necessary to carry out greater changes to public water supply arrangements it must ACKNOWLEDGMENTS provide a rigorous assessment of the economic value and environmental benefits The Environment Agency, Wessex Water of any changes. Consultants, working on and Bristol Water are indebted to the behalf of the Agency have identified a people of the Malmesbury Area, and in range of potential benefits. These benefits particular to those on the Malmesbury have been derived from the following: Liaison Group, for their support during the stream support trials. • a survey of non-use values (see definition below) • a recreational fishing survey • a survey of informal recreation • a study of property price effects Wessex Water Services Ltd Wessex House Passage Street Bristol BS2 OSQ Tel: (0117) 9290611

Environment Agency South West Region Manley House Kestrel Way Exeter EX2 7LQ Tel: (01 392) 444000 Fax: (01 392) 444238

North Wessex Area Office Environment Agency Rivers House East Quay Bridgwater TA6 4YS Tel: (01392) 457333 Fax: (01 392) 452985

Bristol Water Pic PO Box 21 8 Bridgwater Road Bristol BS99 7AU Tel: (011 7) 966588

En v ir o n m e n t A g e n c y

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