Environment Agency RIVER WYLYE Information Centre ENVIRONMENT AGENCY Low Flow Study 128176 FOREWORD N THE RIVER WYLYE LEGEND *“U River Wylye catchment boundary In 1991 the National Rivers River gauging station Authority (now part of the 10 km a Public Water Supply Environment Agency) ^ abstraction borehole commissioned Sir William Halcrow & Partners to study in two phases the influence of abstractions for public water supply on low flows in the Upper Hampshire Avon. In Phase 1, Halcrow estimated the effect of abstraction on all five tributary areas which make up the Upper Hampshire Avon, including the River Wylye. This was completed in 1993. Of the five sub-catchments the Wylye is the most affected by The River Wylye rises from springs in the Cretaceous Upper Creensand of West The PWS sources were all licensed by the abstractions. Beginning in 1993, Wiltshire. The head of the river itself, however, Agency's predecessor authorities. Abstraction Phase 2 focused on low flows in is not always found at the same point. from these sources and conditions on the Depending on the time of year, the licences are carefully monitored and enforced the Wylye and was completed location can be anywhere between the by the Agency. Abstractions from other earlier this year. This leaflet villages of Maiden Bradley and Kingston groundwater and surface sources in the catchment have relatively little bearing on summarises the results, the Deverill. From its source, the river flows north­ eastwards over the Lower Chalk, cutting river flow problems. actions taken and outlines the through the escarpment at Brixton Deverill further work necessary to more and then back onto the Greensand near BACKGROUND Longbridge Deverill. Here the river's flow and fully resolve appropriate action in size is augmented by further spring flows. It Before this study the most notable the Wylye catchment. then flows south-east, again over the Lower hydrological investigation of the River Wylye Chalk and then, from Wylye village, over the was the Upper Wylye investigation of 1972. Middle Chalk, and, beyond South Newton, This was conducted by the River Authority to over the Upper Chalk, on its way to join the investigate the potential for public water River Nadder at Wilton. supply abstraction from boreholes at Brixton Deverill, Heytesbury and Chitterne. The only sizeable tributaries to the River Wylye Abstraction licences were subsequently are the Chitterne Brook, which flows into the granted, with conditions, including a main river between Codford St. Peter and provision for stream augmentation to avoid Codford St. Mary, and the River Till which detrimental environmental damage. flows in at Stapleford. Throughout the 1970s and the 1980s Both the Chalk and the Creensand are gently abstraction from PWS sources in the dipped, relatively thick and highly absorbent catchment gradually increased but within the to water. Consequently, these 'aquifers' allowance of the licensed abstractions. By contain a large volume of groundwater 1990, in the middle of the 1988-92 drought, draining slowly south-eastwards. This makes public claims of low flows in the Wylye caused the Wylye an attractive location for public by abstraction were being received. water supply (PWS) boreholes. Wessex Water Consequently, in 1991 this current study of operates 7 groundwater sources for PWS in the Wylye catchment was commissioned. the catchment and additionally pumps Based on computer modelling of the aquifer- groundwater from two sources in the Upper river system and analysis of historic and newly Wylye to support stream flow during dry collected environmental data the study was periods. in two parts: RIVER WYLYE KEY PLEISTOCENE ALLUVIUM GEOLOGY & RECENT TERRACE GRAVELS MIDDLE CHALK CRETACEOUS LOWER CHALK { UPPER CREENSAND Environmental studies PROGRAMME FOR THE The Agency together with the Wiltshire LONGER-TERM Fisheries Association confirmed a need for To address the most urgent problems the further fisheries and ecological studies to assist Agency is progressing the options for conclusions about the ecological impact of immediate action and early consideration abstractions to support the 'snapshots' taken within our programme of work for 1996/97. during the 1988-92 drought. The following The additional environmental studies will be comprises the Agency's commitments to fill En v ir o n m e n t A g e n c y completed by the 1997 summer. These will the gaps in present knowledge: enlarge on judgements of the impact of i abstractions on the aquatic environment as Survey of local knowledge of the river's concluded in Phase 2 and help to clarify the aquatic environment significance of impacts in the Middle/Lower THE ENVIRONMENT Wylye. By this time we shall also report the The Agency has commissioned a survey of drilling and initial test-pumping of the new local people to record their knowledge of the AGENCY augmentation boreholes. river's environment. This will be used to review the importance of abstractions as an The Environment Agency, which began influencing factor in the Middle and Lower Beyond this we shall also be concerned with operations on 1 April 1996, brought Wylye. The survey report will be ready by the the merits of the additional stream together the National Rivers Authority, augmentation boreholes and a revised end of 1996. Common themes emerging Her Majesty's Inspectorate of Pollution, include complaints that the river channel is pumping regime as assessed over the next over-wide and fish habitat problems are two summers. At this stage, however, it is the Waste Regulation Authorities and related to siltation and the influence of flow premature to suggest what measures may be several smaller units from the and of swans on important aquatic plants. desirable should the continuing work Department of the Environment. demonstrate that radical improvements are Environment Agency fisheries surveys necessary for the main Middle/Lower Wylye. It is apparent that an overall reduction to the The new Agency provides an integrated During 1996-97, the Agency will be quantity of water licensed for public water approach to the protection and conducting the following fisheries surveys in supplies could cause major socio-economic management of the land, air and water the Wylye catchment: difficulties unless an effective strategy is in environment. Its main functions include place to provide alternative sources of pollution prevention and control, waste • A general survey of the fish population drinking water at reasonable cost. This along the entire main river. dimension for the future has already been regulation, flood defence, water • A detailed survey of fish population and raised with Wessex Water and it will be the resources, fisheries, recreation and composition at key sites. intention of the Agency to keep this matter conservation. • A survey of angling quality at various in view in its review of water resources locations in the Wylye at different flows. development strategies. In this respect the • A winter survey of trout breeding success Agency has already commissioned work on as river conditions permit. A particular the costs and benefits of remedies to River REGIONAL OFFICE focus will be the winterbourne tributaries. Wylye low flows as background information Environment Agency to environmental remedies. Manley House The results of these surveys will be compared Kestrel Way with previous studies to help clarify whether We will produce another report in 1997 the adverse changes observed during the incorporating the results of the continued Exeter EX2 7LQ 1988-92 drought are permanent. The angling environmental studies and the latest progress Tel: 01 392 444000 quality survey will help to assess appropriate with the augmentation boreholes and revised Fax: 01392 444238 flow targets. pumping regime. Physical habitat assessment SOUTH WESSEX AREA Environment Agency This project will examine the relationship Rivers House between physical needs of trout and flow in Sunrise Business Park the Wylye catchment. This may make possible Higher Shaftesbury Road a measure of the impacts of abstraction alone, divorced from the other influences at work on Blandford DT11 8ST environmental change. The Institute of Tel: 01258 456080 Hydrology and Worcester College will jointly Fax: 01258 455998 conduct the work which involves habitat mapping, channel description and flow measurement at six locations in the catchment: • in the Upper Wylye near the Deverills. • upstream of Norton Bavant gauging station. ENVIRONMENT AGENCY • the Middle Wylye downstream of Stockton. • the Chitterne Brook at Codford. GENERAL ENQUIRY LINE • the River Till upstream of Stapleford. • the Lower Wylye near South Newton. 0645 333 111 Other related Environment Agency work The Agency has devised a "Land care" project The 24-hour emergency hotline number aimed at controlling inputs of silt and other for reporting all environmental incidents relating to air, land and water. diffuse land-based pollutants to the Hampshire Avon catchment. This includes the ENVIRONMENT AGENCY examination of erosion risk areas within the Wylye catchment with a view to controlling EMERGENCY HOTLINE sediment runoff. The problem of excess algae is also being investigated by the Agency. 0800 80 70 60 SW-10/96-1 k-E-AVFH Printed on Envirocote - A 100% recycled paper PUBLIC WATER SUPPLY SOURCES - MAXIMUM LICENSED QUANTITIES quantity was abstracted then during most summers there would be no flow at Brixton Deverill. Flow impact descriptions for the SITE SOURCE LICENSED DAILY