As part of environmental flows studies, environmental flow compliance calculations are undertaken for a number of climate change scenarios to determine the impact of climate change on environmental flow compliance, as required by the Victorian FLOWS method (DEPI, 2013).
Recommendations for the cool and warm season low flow requirement often include an ‘or natural’ clause, where the lesser of the unimpacted or ‘natural’ flow and the low flow requirement is required. As climate change becomes more severe, the natural flow in the system also significantly reduces. Therefore, due to the ‘or natural’ clause, less water is required at the environmental flow compliance point for compliance under future climate. This can mask the severity of the impact of climate change on environmental outcomes since the reduced natural flow may no longer meet the ecological need for which it was originally provided, for example a level of stream depth or bench inundation.
This investigation will explore the true ecological impact of climate change on environmental flow compliance by allowing natural flow to be modelled unimpacted by climate, or by removing the ‘or natural’ clause entirely for some example catchments. The outcomes of this investigation will be combined with reasonable low flow bounds to achieve ecological outcomes to provide evidence to inform the future treatment of the ‘or natural’ clause when modelling environmental flow compliance under climate change.