Flow metrics for each flow regime area were identified by examining
existing flow metrics for each key part of the flow regime. Learning
from the issues identified in previous flow metric assessments and
considering the communicability of the resulting metrics, simple metrics
were preferred, generally revolving around a number of days. Further to
this, metrics that encompass longer time periods (i.e. annual metrics)
were identified as being preferred as they combined many of the more
specific and ultimately correlated metrics
(Datry et al., 2014a).
The practical application of these flow metrics revolves around linking
them to ecological responses. In order to demonstrate the practicality
of these metrics, EWRs were developed for each for a seasonal river
system. The notion of a pass/fail threshold for ecological systems is
somewhat nonsensical as all ecological systems have a degree of
resilience (Poff, 2018). This is
especially true of seasonal riverine ecosystems the exist in a highly
variable environment (Datry et al.,
2014b). Rather than identify a single threshold based on a long-term
average or individual year, a moving average approach was used to define
boundaries within which the environmental water requirement was
considered to be achieved.
In order to evaluate the metrics, the Barossa Valley Prescribed Water
Resource Area (the PWRA) was used as a case study. The Barossa Valley is
an internationally renowned wine region in South Australia that derives
it water resources from the North Para River and groundwater resources
of the PWRA. The PWRA’s mild, wet winters and hot, dry summers, are
typical of a Mediterranean climate. Annual rainfall varies from more
than 850 mm at high points in the Flaxman Range to about 300 mm north of
Angaston. The surface water resources of the area are heavily developed
with an estimated 1790 dams with an estimated total capacity of 8.1 GL
(Jones-Gill and Savadamathu, 2014,
Montazeri and Savadamathu, 2018). This
represents approximately 52% of the resource capacity (total modelled
runoff with the impacts of water extraction/capture and use removed
(1997 - 2022) (Savadamathu et al., 2023).
Overall about 10% of these dams are licensed under the existing WAP and
account for approximately 60% of the dam capacity.
Ultimately, this report documents the six key ecologically relevant flow
metrics used to quantify the flow regime and the upper and lower limits
of the moving averages for each metrics used to describe the EWRs for
the degraded but stable riverine ecosystems of the Barossa Valley
seasonal rivers.