Candover Licence renewal Part 1 report. DRAFT. 11 August 2016 Renewal of the Candover Scheme Abstraction Licence Part 1 - Hydrological Impact Analysis Final Draft to accompany licence renewal 11th August 2016 Candover Licence renewal Part 1 report. DRAFT. 11 August 2016 We are the Environment Agency. We protect and improve the environment and make it a better place for people and wildlife. We operate at the place where environmental change has its greatest impact on people’s lives. We reduce the risks to people and properties from flooding; make sure there is enough water for people and wildlife; protect and improve air, land and water quality and apply the environmental standards within which industry can operate. Acting to reduce climate change and helping people and wildlife adapt to its consequences are at the heart of all that we do. We cannot do this alone. We work closely with a wide range of partners including government, business, local authorities, other agencies, civil society groups and the communities we serve. Published by: Environment Agency Horizon house, Deanery Road, Bristol BS1 5AH Email: [email protected] www.gov.uk/environment-agency © Environment Agency 11th August 2016 All rights reserved. This document may be reproduced with prior permission of the Environment Agency. 2 of 66 Candover Licence renewal Part 1 report. DRAFT. 11 August 2016 Context of document This is the first in a series of three documents which provide the technical evidence to support our application to renew the Candover Scheme licence in the Summer 2016. Although the licence was varied in 2015 to account for changes necessary to meet the requirements of the River Itchen SAC Habitats Regulations Review of Consents Site Action Plan (2007), the renewal of the licence requires consideration of a greater range of habitats and species and an assessment of impacts on other rivers. Further analysis and changes within the catchment that have happened, or are likely to happen, have resulted in our recommendations to place further constraints on the licence. For that reason this is not simply a renewal of the licence on the same terms, it is a further tightening of conditions on the licence to improve environmental protection. As both the operator of the Scheme and also the environmental regulator determining the permit, this may be viewed as an unusual situation. This document is provided by the Solent & South Downs Area to support our application to renew the licence, which we intend to make in Summer 2016 to allow the licence to be renewed before it expires on 31st December 2016. In accordance with our standard procedures, the recommendation on renewal of the licence will be determined by our National Permitting Service (NPS) with the final decision offered to the Secretary of State for sign off. We are informing a range of local stakeholders about our proposals, giving them the opportunity to comment on this application. To help shape the revised licence, we have sought opinions from Natural England, Hampshire & Isle of Wight Wildlife Trust and our own technical specialists. Natural England will play a formal part in the process of renewing the licence as they are a statutory consultee for abstraction licences that have the potential to affect designated sites. This is the first of three documents that together make-up our assessment of the Candover licence renewal. This report will explain why the scheme is needed and what hydrological impacts it can have on the Candover Stream, River Itchen and surrounding watercourses. The second document follows-on from this hydrological assessment, and is an assessment of the ecological risks and consequences of operating the Candover licence, against the River Itchen SAC and SSSI interest and wider biodiversity. It presents the existing ecological data and considers risks against a number of ecological flow targets. The third, and final document, considers the outcomes of the first two assessments and presents our final conclusions and recommendations on the way forwards. 3 of 66 Candover Licence renewal Part 1 report. DRAFT. 11 August 2016 Executive Summary The Candover Scheme was licensed for use in 1980 following extensive test pumping in 1976. Since that time, the Scheme has been used several times by the Environment Agency during drought events to support flows in the River Itchen. At this time, we believe that the Candover Scheme still has a useful role for managing water resources in the Itchen catchment and so we must renew the abstraction licence before it expires on 31st December 2016. Before the licence can be renewed we need to carry out further assessment to clearly identify any associated environmental impacts when the scheme is used. This report contains the technical evidence to assess the hydrological impacts of the Scheme. We use this GW augmentation scheme to support downstream abstraction during extreme droughts. The current licence accounts for around 2% of all abstractions in the upper Itchen catchment which includes large abstractions for watercress, fish farms and public water supply. This report clearly shows the context in which these impacts are assessed. Abstractions for watercress and public water supply clearly have a far more significant impact on flows than the Candover Scheme as the impacts are larger and persist throughout the year. Use of the Candover Scheme can contribute to those impacts when it is used. The current version of the Candover Scheme abstraction licence, issued in 2015, contains detailed conditions which constrain when and how the Scheme can be used. This means that over the last 60 years, the scheme may have been needed up to 10 times. However, there is the possibility that the Scheme could be used several years in a row under the current terms of the licence: the licence currently allows repeated use. When the Scheme is used, the immediate impact is to increase flows in the Candover Stream and to cause drawdown in the groundwater of the upper Candover valley. The increase in flows in the Candover Stream is managed so that there is a gradual increase, but in the lower reaches of the Stream, flows can still be double what they would otherwise be. Licence conditions ensure that flows cannot rise above the highest flows seen naturally in the Candover Stream for the summer period. Further downstream on the River Itchen, flows typically remain within 10-15% of what would naturally be expected. The introduction of water from the Scheme leads to a lowering of daytime maximum water temperatures in the Candover Stream. There are not likely to be any other water quality impacts from use of the scheme as it introduces groundwater which would otherwise have been flowing naturally into the river system. Once the scheme has been turned off, the lowering of groundwater levels caused by its use results in a reduction in flow in both the Candover Stream and some of the surrounding watercourses - namely the Rivers Dever (in the River Test catchment), and River Wey (in the River Thames catchment), and Alre (upper Itchen catchment). The largest impacts on flows tend to be whilst flows are rising as a result of natural recharge but reductions in peak winter flows are also likely. Depending on how much the scheme has been used and how rapid the natural recharge has been, small scale impacts can persist during the Spring and Summer following use of the scheme and in exceptional conditions, very small impacts can persist for longer than a year. The scale of impact varies, ranging from a maximum reduction in flows of up to 50% in the upper Candover Stream; 10-20% in the middle reaches of the Candover Stream, 5-10% for the lower Candover Stream; and for the River Alre, River Dever and River Wey between 5 to 30% reduction in river flows, reducing after a few months to typically less than 2% for the duration of up to 12 months. 4 of 66 Candover Licence renewal Part 1 report. DRAFT. 11 August 2016 The Candover Stream and surrounding watercourses often have long winterbourne reaches which naturally flow when groundwater levels are high. Use of the Scheme does not affect the pattern of flow in any of these winterbournes, although modelled predictions suggest that the rise in stream heads in the Autumn and subsequent fall in the Spring may be delayed by a few weeks with an typical impact of up to 250m (up to 1.75km maximum) on the location of the stream-head. Compliance with Water Framework Directive tests for both the surface water body of the Candover Stream and associated groundwater bodies has been assessed and use of the Scheme will not prevent achievement of good status by 2027 and will not lead to deterioration in ecological status. 5 of 66 Candover Licence renewal Part 1 report. DRAFT. 11 August 2016 Contents Renewal of the Candover Scheme Abstraction Licence ............................................................ 1 Part 1 - Hydrological Impact Analysis ......................................................................................... 1 Context of document .................................................................................................................... 3 Executive Summary ...................................................................................................................... 4 1. Background ............................................................................................................................... 7 1.1. The River Itchen ..................................................................................................................