Rapid Validation of WFD83 Standards for Freshwater Flows to Estuaries

Rapid Validation of WFD83 Standards for Freshwater Flows to Estuaries
WFD83 Ext.
February 2008

Introduction

Background

The WFD 83 project (SNIFFER 2007) proposed a set of freshwater flow standards transitional waters in the UK. These have been defined to protect estuaries from modifications in freshwater flows resulting from pressures in theupstream catchments (abstraction). The flow standards aim to support Good Ecological Status as well as Moderate Ecological Status.

The standards assigned to transitional water bodies depend on the sensitivity of the estuary to abstraction impacts. This sensitivity has been defined in WFD83 using factors such as freshwater inflow and estuary volume (tidal prism). Each set of standards (i.e. for each level of sensitivity) allow a net level of abstraction from the major (Code 1) freshwater inflows (i.e., in the upstream catchment) for flows of >Qn60, >Qn70, <Qn95 and >Qn95. Code 2 inflows are given a generic set of flow standards regardless of estuary sensitivity, again for each of >Qn60, >Qn70, <Qn95 and >Qn95.

Aims

One of the recommendations from WFD 83 was to validate the proposed flow standards with actual measured data. As a result this project presented here has firstly tested where these standards pass or fail in estuaries, i.e., based on influenced (to approximate actual) flows; and then assessed these results against pressures and specific ecological data. In doing this, the results (i.e., pass or fail in flow standards defined for a particular estuary) have been compared to available environmental information to see whether these are in support. I.e., in a failure we would expect to see environmental impacts of degradation whilst for a pass, we expect a healthy environment.

Report Chapters

The work carried out has been divided into the following chapters:

In Chapter 2 an account of flow standard pass / failure is given as part of the hydrological assessment;
Chapter 3 provides a comparison of these flow standard results against WFD pressures data;
Chapter 4 reports on the comparison of flow standard results with WFD monitoring pilot studies;
Comparisons between flow standards results and fish data are given in Chapter 5; and Chapter 6 provides a conclusion and recommendations from the study.

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