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Abstract:
Degradation of freshwater ecosystems including streams, rivers and wetlands is globally widespread, often driven by water resource development and increasingly exacerbated by climate change. We compared the differential effects of river regulation and climate change, affecting the Lowbidgee Floodplain, a nationally important wetland ecosystem within the Murray-Darling Basin in semi-arid Australia. We first modelled natural flows in the lower Murrumbidgee River, using runoff from the upper catchment, and compared them to actual river flows impacted by extensive water abstractions and dam constructions over more than a century. We then developed a model for future flows under river regulation and different climate change scenarios. We also modelled changes to the frequency of overbank flows, affecting the amount of water reaching the Gayini Wetlands. Our preliminary findings suggest that annual mean river flows under actual regulated conditions were about 30% lower than modelled natural river flows since 1990. We also found that mean annual river flows would decrease by another 6-15% due to projected climate change until 2075. The average number of days per year with major floodings was predicted to drop by 71-78%, relative to historic natural river flows. We discuss the implications of our findings for the long-term future of the Lowbidgee Floodplain and the restoration of the Gayini Wetlands by the indigenous Nari Nari Tribal Council, relying on its ecosystem functions and services. We developed a structured approach based on simple hydrological modelling, applicable to any river systems around the world to inform large-scale river and wetland restoration.
