Estimation of the environmental risk of regulated river flow

- Environmental risk model for estimating environmental risk of a river system.
- Unsatisfied environmental flow demand cause environmental risk.
- Environmental risk time series provides guideline for meeting environmental flow demand.

SummaryA commonly accepted paradigm in environmental flow management is that a regulated river flow regime should mimic the natural hydrological regime to sustain the key attributes of freshwater ecosystems. Estimation of the environmental risk arising from flow regulation needs to consider all aspects of the flow regime when applied to water allocation decisions. We present a holistic, dynamic and robust approach that is based on a statistical analysis of the entire flow regime and accounts for flow stress indicators to produce an environmental risk time series based on the consequence of departures from the optimum flow range of a river or reach. When applied to a catchment, (Campaspe River, southern Australia) the model produced a dynamic and robust environmental risk time series that clearly showed that when the observed river flow is drawn away from the optimum range of environmental flow demand, the environmental risk increased. In addition, the model produced risk time series showing that the Campaspe River has reversed seasonal patterns of river flow due to water releases during summer periods, which altered the flow nature of the river. Hence, this resulted in higher environmental risk occurring during summer but lower in winter periods. Furthermore, we found that the vulnerability and coefficient of variation indices have the highest contributions to consequence in comparison to other indices used to calculate environmental risk.