Salt Wedge Dynamics and Responses to Environmental Flow Releases

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Christine Lauchlan Arrowsmith, Andrew McCowan

Thursday 2 july 2015

11:30 - 11:45h at Europe 1 & 2 (level 0)

Themes: (T) Managing deltas, (ST) Saline and freshwater interaction

Parallel session: 11K. Managing deltas - Saline

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Environmental flow releases are used to provide targeted river flows to meet ecologically important physical outcomes. For an estuary, these river flows can impact water levels as well as salinity conditions. Recent environmental flow releases have been undertaken for the Latrobe River estuary system to address the water requirements of the estuary ecology as well as that of the adjacent wetlands. The Latrobe River estuary connects the catchments of the Thomson, Macalister and Latrobe Rivers with the Gippsland Lakes. The ecological conditions of this estuary system has been significantly impacted by water resource development within the catchments as well as changes to the salinity regime of the Lakes as a result of a permanent artificial entrance to the ocean being constructed in the late nineteenth century. An environmental flows study established a series of environmental objectives and flow recommendations for the estuary which focussed on freshwater inflows to manage salinity. Based on the flow recommendations, environmental flow releases aimed at meeting ecological requirements were made during 2014. The impact and effectiveness of these flow releases was assessed through an extensive physical monitoring program which recorded salinities, water levels and flows throughout the estuary. The results of the monitoring show that environmental water released from upstream reservoirs can have a measurable short term impact on salinity conditions in the estuary; however the duration and magnitude of the releases may limit longer term ecological responses. Combining the knowledge gained during the monitoring program with the ecological requirements of the estuary and wetlands, designs have been developed for regulating structures to maximise the benefits of environmental flows.