Complexities of opening and closing the Gellibrand River estuary for water quality management

Ms Amanda Shipp1

1Alluvium, Cremorne, Australia

Abstract

Over 80% of Victoria’s estuaries periodically close to the sea. Closures are a natural process, however extensive flooding can occur when an estuary mouth is closed, impacting on public and private assets and productive use of the floodplain. As a result, estuaries are sometimes artificially opened with earth moving equipment. This process can lead to low dissolved oxygen conditions in the water column and fish deaths.

The Gellibrand River estuary has a complex history of management regarding the open / closed state of the estuary mouth. Periods of low dissolved oxygen (DO) concentrations historically occur during prolonged periods of estuary closure to the ocean, however also occur with artificial estuary opening. We completed an investigation using a data-driven approach to understand the factors influencing water quality conditions both in a closed estuary and immediately after artificial openings.

The investigation produced a framework to assess the likely impact on dissolved oxygen from keeping the estuary closed, vs the impact from artificially opening. Guidance on when to open was developed, which including limiting water extractions during key times . The project included a live trial of using the framework to inform management actions.  This approach could also be applied to other intermittently closed estuaries (ICE) to overcome artificial estuary opening and water quality management issues.

Biography

Amanda is an environmental engineer at Alluvium. Amanda specalises in fluvial and estuary processes and water resource investigations, and developing conceptual and technical solutions to complex problems.

About the Association

The Australian Coastal Society (ACS) was initiated at the Coast to Coast Conference in Tasmania in 2004. The idea was floated as a means for those interested in coastal matters to communicate between conferences and where possible take resolutions of the conference to appropriate levels of government.

The idea was discussed further at the Coast to Coast Conference in Melbourne in 2006 and it was agreed that Bruce Thom develop a constitution of a company limited by guarantee that would operate on a national basis.

This plan was accomplished and in 2008 at the Coast to Coast Conference in Darwin the constitution was ratified and an Executive appointed. The company received charitable status in 2011.

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