Salinity, Water Level, and Flow Considerations for Assessing Environmental Water Requirements of the Lower Latrobe River (11598)
The lower Latrobe River is an estuarine system which connects the catchments of the Thomson, Macalister and Latrobe Rivers with Lake Wellington and the Gippsland Lakes. The estuarine conditions of the river are unusual, as its distance from the ocean entrance of the Gippsland Lakes results in a micro-tidal water level range, with water levels in the Lake Wellington and lower Latrobe River dominated by winds, waves and atmospheric pressure as well as the effects of upstream river inflows. Salinity conditions are also highly variable, ranging from predominantly fresh to almost ocean salinity during the recent extended drought period. Salinity is a crucial factor with regard to the ecological condition of the system and an environmental flows study investigated how environmental water could be used to moderate the effects of increasing salinity regimes as well as meet the ecological objectives of the system as a whole. Hydrodynamic modelling was used to assess the flushing behaviour of freshwater inflows on the lower river and this behaviour was then linked back to the ecological requirements. Environmental flow recommendations were developed which focussed on freshwater inflows to manage salinity, along with more typical criteria around flow inundation in terms of water levels and frequency. Quantification of these recommendations was made possible through the detailed hydrodynamic modelling.