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.