E-flows: from concept to implementation
Abstract
Lindsay Island in northwestern Victoria supports a range of significant flora and fauna, sites of indigenous heritage and Murray River floodplain landforms: riverine lakes, billabongs, anabranches, numerous flood-runners and other preferred flowpaths. Floods are central in structuring the channel, wetland and floodplain ecosystems and provide important links between the Murray River and its surrounding environment. However, the flow regime of the Murray River has been subject to marked changes in recent times. River regulation has impacted ecosystems by changing the frequency, timing and duration of the floods that support them. This paper presents the findings of a number of investigations into the environmental water requirements on Lindsay Island and their provision via regulators and other floodplain infrastructure. The environmental water problem on Lindsay Island is extremely complex with flow stresses that vary considerably across the floodplain environment and through the year. To provide a framework to consider integrated flow management and delivery options we defined water management units (WMUs) on hydro-geomorphic criteria. We then developed a series of flow objectives based on the known flow requirements of key biotic and abiotic processes of each of the WMUs. Based on flow objectives, we identified particular components of the flow regime critical for the maintenance or rehabilitation of the floodplain environment. For the riverine lakes and billabongs of Lindsay Island we related flow objectives to stage height, period and frequency of inundation and Murray River flows. The longitudinal and lateral connectivity requirements of the stream ecology, along with aspects of sediment movement and saline groundwater discharge formed the basis of our assessment of the island’s anabranches and floodrunners. Feasibility studies of various regulating structures indicated a range of potential regulation devices to achieve the critical flow components. In the near future, these structures will regulate flow into and through the floodplain features of Lindsay Island to return some of the missing flow-related values to this uniquely Australian environment.