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.