Ecological Assessment of Environmental Flow Reference Points for the River Murray System

"October 2003".

MDFRC item.

Background 1. There is considerable evidence that the overall health of the River Murray system is in decline and no longer in a sustainable condition. While the effects of such decline are more immediately obvious in some parts of the river system than others, the scientific evidence for overall loss of river health is strong. 2. There are multiple threats to the health of the River Murray system. These include changes to flow regime, habitat destruction, increased salt and sediment load, loss of connectivity due to structural alterations, unsustainable floodplain management, and introduction of exotic pests. Of these threats, changes to flow regime are critical and require immediate attention if the River Murray is to be returned to a 'healthy working river’ condition, and maintained that way for future generations. Other threats are being addressed by the MDBC under related programs covered by the Living Murray process, and the MDBC Integrated Catchment Management strategy. 3. Following earlier investigations, in April 2002, the Murray-Darling Basin Ministerial Council called for a comprehensive assessment of the costs and benefits to the environment, industries and communities of returning additional water to the River Murray as environmental flows. The Ministerial Council chose three environmental flow 'reference points’ for analysis; 350, 750 and 1500 GL/yr. Proposed structural and operational modifications were also to be assessed. An independent Scientific Reference Panel (SRP) was contracted by the MDBC in October 2003 under the chair of Professor Gary Jones, Chief Executive, Cooperative Research Centre for Freshwater Ecology to advise the MDBC and Ministerial Council on potential ecological benefits. 4. The MDBC provided the SRP with three different operational scenarios to be assessed for each of the flow 'reference points’. These scenarios were not proposed water recovery or management options, rather, examples of what may be achievable through improved river operations. For each of the 350, 750 and 1500 GL options a 'Cap’, 'b’ and 'c’ operational scenario was assessed. The 'Cap’ option provided an environmental flow regime based on current river operational rules. The 'b’ and 'c’ options were based on modelled flows targeting various ecosystem locations and specific ecological indicators. 5. This report presents the interim results of the ecological assessment undertaken by the SRP up to August 2003, with minor modifications made in October 2003 in response to international peer reviewers’ comments. It provides estimates of 'ecological potential’ for the reference points under consideration. It is designed to serve as a basis for discussion and review amongst scientists, government officials and the broad community. It is not the definitive or final statement of the SRP on ecological benefits potentially arising from the flow volume reference points. The final report is due for submission to MDBC in mid-2004.