Guidance on Environmental Flow
Releases from Impoundments to Implement The Water Framework Directive
Project Extension 1
– Practical methodology for assessment GES for impoundments
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
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.
The report is available for download from the SNIFFER Website