Connectivity is a recurring theme across human cultures and a central tenet in the scientific understanding of ecosystem function. Where connectivity is fragmented, ecosystem health and societal well-being decline. At the terminus of Australia’s largest river system, the Murray-Darling, over 7 km of tidal barrages form an abrupt physical barrier between the river and its estuary, profoundly altering natural freshwater–estuarine–marine connectivity. Combined with reduced river flow, barrage operation has contributed to declining estuarine ecosystem health, with associated cultural and economic consequences. Climate change is expected to intensify these pressures through further reduction in freshwater inflows, increasing sea levels and increased risk of barrage overtopping.
Globally, to improve the health of rivers and estuaries, operation of tidal barriers is progressively shifting towards approaches that enhance hydrological connectivity and promote more dynamic estuarine interfaces. Here we present a study exploring improved hydrological transparency—facilitating bidirectional water exchange through the tidal barrages— to improve estuarine ecosystem function. In an anthropogenically modified river system, however, increased connectivity also presents risks, particularly the intrusion of saline water into a terminal freshwater lake system that is used for consumptive water supply and supports threatened freshwater biota. As such, this project aimed to improve understanding of the benefits and risks associated with more transparent barrage operation. We used a combination of computational modelling, in situ measurements and biological monitoring to: (1) assess the influence of more transparent barrage operations on hydrodynamics, water physico-chemistry and ecosystem processes and (2) evaluate ecological responses, with a focus on the movement, habitat use and spawning of key fish species. These components will be integrated within a hydro‑ecological modelling framework to inform adaptive barrage management and identify opportunities to facilitate the bidirectional movement of water and biota through the barrages, including under climate change and sea-level rise scenarios.