Environmental flows case study in the Daly River

There is increasing pressure to develop the water resources of tropical northern Australia but we currently have limited capacity to predict the consequences of altered flow regimes on aquatic plants and animals. To address this, we have recently completed a project that will contribute to water allocation planning in the wet-dry tropics by quantifying the environmental flow requirements of fish in the Daly River and predicting the ecological risks of alternative water use scenarios. Quantitative risk assessment models (Bayesian Belief Networks) were developed using information on modelled changes in dry season flow regimes under various water extraction scenarios, combined with outputs from two-dimensional habitat simulation models of fish species' hydraulic habitat requirements, and other scientific data and Indigenous ecological knowledge. The models were developed and validated for five key river reaches using fish sampling data collected over a three-year period. We conclude by arguing that Bayesian Belief Networks provide an ideal way of combining quantitative data with expert knowledge (where such data is lacking) to inform environmental flow management and planning.