Simplified Environmental Flow Metrics and Environmental Water Requirements for Mediterranean Seasonal Rivers

The flow regime of a river is well established as being one of the key drivers of riverine ecosystem type, diversity and condition. This is especially true of seasonal rivers that experience a cease to flow period over the dry months of the year. To effectively assess changes in the components of the flow regime, it is required that flow data be quantified into metrics for ease of assessment and to effectively relate changes to environmental outcomes. Previous methods have used large numbers of, often complex, flow metrics to assess the flow regime. These metrics are often highly internally correlated with each other, and their complicated nature makes communication difficult. We suggest that the high correlation and the targeted nature of ecological flow regime assessment means a smaller number of well selected metrics can be used more effectively that large suites of generic metrics. We report on a series of six flow metrics that cover the whole of the flow regime, are reported annually and are simple to assess and interpret. We further expand on the practical use of these metrics as environmental indicators in their application to the highly variable seasonal rivers of southern Australia by using a moving average approach rather than single years. This approach accounts for, and allows for, the interannual variability expected in these systems. Environmental water requirements are defined using upper and lower bounds of a moving average for each metric over an environmentally stable period. We argue that this approach represents a more representative and robust approach to the assessment of environmental water requirements that is simpler and easier to interpret and communicate that existing flow regime assessment methods.