The role of coastal processes in the management of the mouth of the River Murray, Australia: Present and future challenges

The Murray-Darling Basin is the largest river system in Australia to enter the sea. Prior to regulation of water flows, the Murray Mouth remained open to the sea even during droughts. An open mouth assists in sustaining the ecology of a Ramsar listed wetland and enables the flushing of salt, nutrients, and suspended sediments to the sea. Construction of barrages designed to prevent saltwater ingress has separated the estuary into two sections, a set of freshwater lakes and a saline tidal lagoon area, creating a unique set of management challenges. Under current overextraction of water resources upstream, river flows have been largely insufficient to counter wave and tide processes, which propel marine sands thereby constricting the Murray Mouth. Dredging has been required to maintain an open entrance. Managing this system is part of a 2012 agreement between state and federal governments, through the Murray-Darling Basin Plan. This plan recognizes a healthy end of system; however, the hydrological models failed to factor in the power of the sea in blocking the Murray Mouth. The plan requires that there will be sufficient river flows for the mouth to be open 95% of the time without dredging. Currently, sand ingress from the sea requires dredging most of the time. It is unlikely that there will be sufficient river flows to counteract continued sequestration of marine sand into the mouth. Sea level rise and decreased rainfall in the southern half of the Basin under climate change conditions will require a review of management options to prevent the long-term degradation of the end of system.