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.