Hydrology Assessment June 2017 Lower Test Project: Hydrology assessment of Proposed Licence Changes to Testwood PWS and Lower Test Flow splits sensitivity analysis June 2017 Hydrology Assessment June 2017 Contents 1. Background ................................................................................................................... 3 2. Aim of Report ................................................................................................................ 4 3. River Test Catchment Description ................................................................................. 4 4. Resource Assessment .................................................................................................. 6 4.1 Environmental Targets ................................................................................................ 7 4.1.1 EFI ....................................................................................................................... 7 4.1.2 Salmon migration protection flow requirements criteria ......................................... 8 4.1.3 River Test and Lower Test Valley SSSIs and Solent & Southampton Water Ramsar habitats and species Criteria ............................................................................ 8 4.2 Flow Data .................................................................................................................... 9 4.2.1 Gauged Data ........................................................................................................ 9 4.2.2 Natural Data ....................................................................................................... 12 4.3 Artificial Influences .................................................................................................... 15 4.4 Additional Assessment Points in Ledger .................................................................... 17 5. Current Lower Test WR Assessment ........................................................................... 17 6. Licence Change Options ............................................................................................. 20 6.1 Option 1: Change licence conditions to meet EFI ...................................................... 21 6.2 Option 2: Change licence to Average Recent Actual Quantities ................................ 23 6.3 Option 3: Change current HoF to the in-river salmon migration protection and salmon entry protection HoFs ...................................................................................................... 23 6.4 Option 4: Change current HoF to the in-river salmon migration protection and salmon entry protection HoFs along with a reduction in licence quantities to meet EFI ................ 24 6.5 Option 5: Change licence to Voluntary Licence conditions ........................................ 26 6.5 Option 6: Alternative Management – Flow Splits ....................................................... 28 6.5.1 Methodology: Reduce Broadlands Fish Farm Carrier flow by 60% ..................... 28 6.5.2 Methodology: Coleridge Award Fixed flow split ................................................... 29 6.5.3 Reduce Broadlands Fish Farm Carrier Flow and use Coleridge Award Fixed flow split ............................................................................................................................. 30 6.5.4 Alternative Management Option Results ............................................................. 31 7. Change in Abstraction Sensitivity and EFI for the Test ................................................ 32 7.1 ASB3 High Sensitivity ................................................................................................ 32 7.2 ASB13 Transitional waterbody .................................................................................. 33 8. Conclusions ................................................................................................................. 34 References ......................................................................................................................... 35 Hydrology Assessment June 2017 1. Background To manage water effectively we need to understand how much is available and where it is available, after considering the needs of the environment. This is achieved by undertaking a resource assessment. Over many years we have assessed the impact of abstraction throughout the River Test. In 2000 we developed the Catchment Abstraction Management Strategies (CAMS) process as a consistent national tool for managing abstraction. The CAMS process was updated in 2013 to produce Abstraction Licensing Strategies (ALS) to help set out how we will manage the water resources of a catchment and contribute to implementing the Water Framework Directive (WFD). The ALS process sets out a nationally consistent Resource Assessment Method (RAM). Water availability is determined by the relationship between each of the following main components of RAM: a resource allocation for the environment defined as a proportion of natural flow, known as the Environmental Flow Indicator (EFI); the Fully Licensed (FL) scenario - the situation if all abstraction licences were being used to full capacity; the Recent Actual (RA) scenario – the amount of water which has actually been abstracted on average (usually over a set timeperiod). The first Test & Itchen CAMS in 2006 (Environment Agency, 2006) indicated that at low flows the Lower Test catchment are “over-licensed”. This means that if existing licences were used to their full allocation they would have the potential to cause unacceptable environmental impact at low flows but that current actual abstraction is resulting in no water available at low flows. While the main aim of the abstraction management process is to set out how we deal with future abstraction it also identifies sites that are potentially being adversely affected by abstraction for inclusion in the Restoring Sustainable Abstraction (RSA) programme for investigation as funding and resources allow. The 2006 CAMS and subsequent ALS identified concerns about the Testwood Public Water Supply (11/42/18.16/546) abstraction impact at fully licensed quantities on the River Test. Testwood is Southern Water’s largest single licence, located close to the tidal limit of the River Test. Testwood was therefore entered into the RSA programme and Southern Water began their National Environment Programme (NEP) for AMP 5 (2010 – 2015) to investigate Testwood’s impact on the Lower Test SSSI in 2011, after the precursor Environment Agency RSA project from 2009-2011. The Southern Water NEP concluded that there was minimal risk to the environment from both current and full use of the licence (Atkins, 2013). Although we agreed that current abstraction levels do not appear to be having a significant impact on the River Test and Lower Test Valley SSSIs, we disagreed with Southern Water about the risk of potential impacts associated with increased abstraction levels. We believe that it is necessary to reduce the Testwood abstraction licence to prevent any risk of deterioration and to ensure protection of SSSI habitats and species and the downstream Ramsar site. Southern Water have indicated that they believe that the licence should be reduced but, due to the lack of information provided to show there is no risk of deterioration, there is no agreement with them about the changes needed. Southern Water also contend that the Environment Flow Indicator and other target flow regimes should not apply in an environment affected by structures diverting flows and impounding rivers and so options of alternative river management could be considered to achieve the environmental objectives. No firm options have been proposed and so work is ongoing to change the Testwood licence to be a more sustainable abstraction. Hydrology Assessment June 2017 2. Aim of Report This report has been produced to demonstrate current compliance conditions in the River Test and to test the environmental sustainability of options for changing the Testwood Public Water Supply Licence. The report will assess a set of proposed licence change options compared to the environmental outcomes measured by changes in flow set by the NEP project. This report does not discuss or validate the environmental outcomes. Southern Water have been considering catchment management options including ways to modify the Lower Test flow splits to contribute the environmental objectives. No firm options alternative management option have been proposed. The secondary aim of this report is to complete a sensitivity analysis to assess whether there is any real benefit in managing the flow diversions to the environmental outcomes. It must be noted that the flow diversions in the Lower Test area are unlikely to have a significant effect on overall total flows entering the estuary, and all the diversions and offtakes are privately owned and are not currently subject to regulation and so the EA has no part in enforcing or managing the flow in those channels 3. River Test Catchment Description Detailed information on the catchment including the hydrology (river management, flow splits and diversions) of the lower River Test (from Timsbury to the estuary) was compiled by the Environment Agency as part of its Lower Test Project in 2009 and reported in the Baseline Data Report (Environmental Agency, 2010a) & Flow Diversion Scoping Report (Environment Agency, 2010b). A summary of this information is presented in this report. The River Test is a