Expert Panel Evaluation of Risk Assessment for Chowilla Regulator

"August 2009".

Project Number: Expert Panel Chowilla Environmental Regulator - 500.17.

MDFRC item.

The Chowilla floodplain and anabranch system is a significant ecological asset of the Murray-Darling Basin; it is an Icon Site of the Living Murray and is a RAMSAR listed wetland of international importance. Although the Chowilla floodplain is currently undergoing a severe decline in environmental condition owing to river regulation and prolonged periods of low in-flows, it still retains much of its natural character. Discrete areas of floodplain have benefited from an environmental watering program which has been conducted here since 2004. However, owing to constraints with the delivery of environmental water these programs are only conducted on a small scale and much of the rest of the floodplain continues to decline. Despite dramatic declines in fish populations in the lower Murray River, Chowilla remains an important site for native species. It has abundant small-bodied species, the presence of several threatened species and good populations of Murray cod and callop (yellow belly or golden perch), both popular angling species. These latter two species are associated with fast-water habitats in the inflowing creeks, rather than the slow weir pools of the Murray River. The Murray cod population appears to have regular spawning and recruitment, one of the few sites where this occurs in South Australia. Native fish populations in Chowilla should further benefit from the recent addition of fishways to barriers in the lower Murray river.

A range of management options to halt the decline of the Chowilla floodplain and to meet The Living Murray’s First Step Decision have been evaluated. Brookes et al. (2006) concluded that the construction and operation of an environmental regulator on Chowilla Creek to artificially inundate a large portion of the Chowilla floodplain was the only option considered that came close to meeting these objectives. However, they cautioned that owing to the scale of the project being considered detailed assessments of the potential risks involved in the operation of the regulator should be undertaken before a final decision was made.between 2007 and 2009 a series of detailed investigations and risk assessments have been undertaken for a range of assets that may be affected by regulator operations. These included abiotic factors such as floodplain geomorphology, surface water quality and ground water, surface water and soil salinity interactions. Flora and fauna responses to regulator operation where also considered including predicted responses of avifauna, amphibians, fish, pest plants and terrestrial vegetation (including both trees and understorey vegetation). The risk assessments are summarised in the document Environmental assessments of the Chowilla Creek environmental regulator (SA Murray-Darling Basin NRM Board, 2009) The panel who contributed to the Brookes et al. (2006) report of potential risks and benefits were reconvened to review the individual risk assessments that were undertaken in response to this report. The panel were asked to comment on four points: The adequacy and breadth of ecological assessments completed to date, - The balance of risks and benefits and potential tradeoffs associated with regulator operation vs no action, - A recommendation on whether or not to proceed to construction based on the potential risks and benefits, and, if the project proceeds -Recommendations regarding ongoing operation.