Methods

Data for this assessment as sourced from two key locations. Observed flow data was accessed for a series of flow monitoring stations across the PWRA. A total of six flow stations were used for the assessment with data accessed from Water Data SA (Department of Environment and Water, 2023). Only verified data was used for the assessment with no interpolated data included. Modelled flow data was sourced from a surface water model run using eWater Source (eWater, 2022) developed for the Barossa by Jones-Gill and Savadamathu (2014) and updated by Montazeri and Savadamathu (2018) run for the period 1969 – early 2023. Two modelled scenarios used in this assessment; the modelled current scenario that represents the current hydrological situation in the PWRA, and the no dams/extraction scenario which reflects a scenario with water capture and extraction removed, referred to as the ‘no dams’ scenario.
All metrics calculated are based on years with a minimum of 95% of data present to avoid missing data being interpreted as days below relevant thresholds. The flow year is considered to be from December – November to capture the full flow seasons as the low flow season spans December - April.

Zero flow threshold

The zero flow threshold is the cut off used to describe a flow being zero in the modelled data. The modelling software will attenuate daily flows down to 1 x 10-5 ML/day (10 litres per day). Flows this low are nonsensical in reality, therefore a threshold is applied. Previous assessments in the Barossa have used the 0.05 ML/day threshold based on Green et al. (2014). Other environmental water planning assessments in the Mt. Lofty Ranges have used no threshold (e.g. VanLaarhoven, 2012, VanLaarhoven and van der Wielen, 2009). The zero flow threshold used for this assessment was established by comparing the number of flowing days in the observed flow data and the modelled current data from the eWater Source model. Several thresholds were assessed including zero (no threshold), 0.015 ML/day, 0.03 ML/day, 0.04 ML/day, 0.05 ML/day and 0.1 ML/day. The threshold used was selected based on the highest correlation (Pearson correlation coefficient) and the degree of overlap with the observed data.

Flow metric assessment

All of the flow metrics developed applied the zero flow threshold identified for modelled data. Observed data was used with no modification. Where suitable observed data was available, this was used in preference to the modelled current data.