Discussion
The ability to represent the entire flow regime in a simple yet
scientifically robust series of six environmentally relevant flow
metrics represents a significant simplification in from the superfluous
manner in which the flow regime of seasonal rivers are represented and
assessed. This simplification is evident both in regards to the number
of flow metrics used (e.g. compared to 56 in
VanLaarhoven and van der Wielen (2009) or
120 in Kennard et al. (2010)) and in
regards to the complexity of the metrics themselves. The results of the
correlation assessment show that there is enough differentiation between
the metrics that they all individually add significant information to
the overall narrative. While it is clear that the additional functions
of the flow regime (e.g. Yarnell et al.,
2020) could have been identified (e.g. overbank flows, variability
within flow season etc.), it was determined that these would have added
excess complication to the process without adding sufficient additional
information to the assessment. This was considered especially important
as a significant role of these metrics will be to communicate flow
regime changes to community groups and other non-scientific
stakeholders.
The metrics that been identified are all simple metrics reported as
annual values. This provides benefits over previous complex metrics or
metrics that are calculated over the entire time series. Time series
metrics allow for more detailed investigations into changes through
time, especially relevant when considering the implications of a
changing climate. The impacts of climate change on flow regime are
likely to be a significant focus both for these metrics and in the
broader seasonal rivers field akin to
Dhungel et al. (2016).
The use of set threshold values identified from outside the flow data
itself was possible for the Barossa as there was only two locations
where this was required to inform the process, with the remaining values
portioned by catchment area. This provided a tangible link to the
physical environment and a clear line between observed information, the
metrics and associated EWRs. This may prove difficult for larger areas
where information may not be available (e.g. permanent pool depth for
pool volumes) or where the number of locations to be assessed is
prohibitively large to do individual threshold assessments.
For the development of low flow thresholds, it was noted that the
threshold values were close to the lower inflection point of the flow
duration curve for the site. This could provide a method for identifying
the low flow threshold from within the flow data. This will remove the
direct link to a tangible on ground measure but should retain the
overall functions defined for the low flow metric described in table XX.
With the high correlation observed in other flow metric sets within the
same flow season, it is highly likely that any flow threshold used close
to the lower inflection point of the flow duration curve will be highly
correlated with a value identified from the physical assessment used
here. Therefore, they would be likely to convey the same information for
flow regime assessment. The same argument could be made with the
commence-to-flow threshold used for the assessment of the
break-of-season. The identification of the threshold could be achieved
by identifying the inflection point of the cumulative flow post April
1st and averaging the flow value over the time series.
Ultimately, the six flow metrics were able to provide a basis for the
establishment of EWRs for the region based on the premise that the
ecology of the region was stable between 1997 and 2016. This ability to
not only characterise the flow regime, but the relationship of the
environment to it, and quantify thresholds that can be used as
management triggers or levers provides a powerful tool for managers and
researchers alike but is simple enough to be interpreted by the broader
public. By quantifying these thresholds based on a moving average rather
than an individual year, it provides a more meaningful representation of
the impacts on the riverine ecosystems in an inherently highly variable
system.