Guidance on Environmental Flow Releases from Impoundments to Implement The Water Framework Directive
Project Extension 1 – Practical methodology for assessment GES for impoundments
March 2008

Executive summary

Implementation of the EC Water Framework Directive (WFD) requires the development of procedures to ensure the adequate mitigation of the negative impacts created by water abstraction and impoundments. Flow regime releases from impoundments, such as reservoir dams, will be included in the licence conditions to allow the proper mitigation of negative impacts caused by their construction and operation.

This report provides a practical methodology for implementing the WFD82 Standards for the initial assessment of whether a water body is likely to fail to meet Good Ecological Status (GES) because of changes to the flow regime (indexed by simple flow regime statistics).

The availability of information on the release of water (spills and compensation flows) from reservoirs is the biggest barrier to implementing a methodology for testing whether a water body is likely to fail to meet GES.

The methodology is a risk based framework based upon the use of the reservoir impact simulation model within the Low Flows 2000 software system in conjunction with a simple, water balance based reservoir simulation model.

The approach enables regulators to apply the methodology in a screening level mode using worst case, minimum data scenario. The framework then provides the opportunity to improve the accuracy of the assessment by improving the data used to predict the releases from the reservoir, and hence improving the release profile used within the Low Flows 2000 reservoir impact simulation model.

All guidance is provided within the limits of current knowledge of the flow regime requirements of river ecosystems, the likely impacts of flow alterations of ecosystem status and the current modelling capabilities of the Low Flows 2000 system.

Copies of this report are available from the Foundation, in electronic format on CDRom at 20.00 + VAT or hard copy at 25.00, less 20% to FWR members.

N.B. The report is available for download from the SNIFFER Website