Median and high flows
Flow metrics representing the medium and high flows were developed based on values reported in Jones-Gill and Savadamathu (2014). The threshold for medium flows was defined as the median (50th percentile exceedance) of non-zero daily flows for the modelled current scenario. Likewise, the threshold for high flows was defined as the 20th percentile exceedance of non-zero daily flows for the modelled current scenario. These thresholds were applied across all scenarios, i.e. the threshold was not recalculated for different scenarios. Using the same threshold regardless of scenario removes the issue with using non-zero flow metrics relating the changing portions of zero flow (changing baselines).

Establishment of environmental water requirements

The EWRs for the current ecosystems present in the PWRA was identified by examining the results of the flow metrics over the last approximately two decades. Concurrent work has identified 1997 – 2022 as a time window reflective of modern flow conditions that includes the Millennium Drought, several high rainfall years and the recent extreme variability (Savadamathu et al., 2023). The environment was considered stable up until the start of the extreme variability observed post 2017. Therefore, a baseline period of 1997-2016 was used to establish the expected and acceptable range of variability within each of the metrics, characterised as the upper and lower limits of a three-year moving average for each metric. Three years was identified as it is the general maximum life expectancy of Mountain Galaxias (McNeil and Hammer, 2007), a high priority ecological asset in the region. Post 2016, metrics were assessed as either meeting or failing the EWR by the three year moving average rather than the individual metric result for each year.