2.5.2.1 Water balance based on the AWRA-L model

Surface water balances are reported for three consecutive 30-year periods, each with different rainfall inputs to reflect a temporally trended climate signal. Licensed extractions from surface water for non-mining uses are not reported because they are unable to be represented in the Australian Water Resources Assessment landscape model (AWRA-L). Such extraction can be modelled using the Australian Water Resources Assessment river model (AWRA-R), however in the absence of significant regulation and consumptive water use, AWRA-R has not been used in this study. The impact of licensed extractions of groundwater for CSG is reflected in changes in the upward flow from the deeper groundwater system as modelled in the groundwater model. The impact of the additional coal resource development (the West Casino Gas Project), calculated as difference between the coal resource development pathway (CRDP) and the baseline (presented in Table 5 to Table 9), reflects the impacts of CSG development only, as the climate signal is identical in both modelling runs. The changes in corresponding values over the three reporting periods encompass the effects of both climate and the coal resource development. Note that the values in the difference column are calculated individually for each of the 30 model runs, and the summary differences presented (i.e. median of the differences, not difference of the medians). The median, 10th and 90th percentile of water balance components derived from the selected 30 AWRA-L model runs are presented in this section.

This section provides summaries of the total water balance calculated at four surface water locations in the Richmond river basin for each of the three 30-year periods. These locations are:

The effect of climate change in the water balance for the Richmond river basin is very small given the projected climate signal in the current model. There is a decreasing trend in the rainfall which translates into a decreasing trend in the surface water outflow and groundwater recharge. However, the magnitude of the change is very small with less than 2% decrease in rainfall and surface water outflow and slightly more than 1% decrease in groundwater recharge when the 2073 to 2102 period is compared to the 2013 to 2042 period for the baseline.

2.5.2.1.1 Water balance for Eden Creek (model node CLM002)

The catchment area above model node CLM002 is 696 km² and is within the West Casino Gas Project extent. The difference in the modelled water balance between the CRDP and the baseline at Eden Creek is in the total surface water outflow over each of the three 30-year periods (Table 5). Note that differences of less than 0.05 GL will appear as 0.0 GL in the table (0.05 GL over 30-year period is less than 2 ML/year).

Table 5 Surface water balance totals at Eden Creek (model node CLM002). Results summarise the range in the 30 groundwater model runs for each of the three climate periods modelled in the Clarence-Moreton bioregion

Three numbers are provided for surface water outflow. The first number is the median, and the 10th and 90th percentile numbers follow in brackets.

NM = data not modelled

Data: Bioregional Assessment Programme (Dataset 1, Dataset 2)

2.5.2.1.2 Water balance for Shannon Brook above Yorklea (model node CLM007)

The catchment area above model node CLM007 is 498 km² and is within the West Casino Gas Project extent. The difference in the modelled water balance between the CRDP and the baseline for Shannon Brook is the total surface water outflow over each of the three 30-year periods (Table 6). The difference was less than 0.2 GL for all three of the 30-year periods. Note that differences of less than 0.05 GL will appear as 0.0 GL in the table (0.05 GL over 30-year period is less than 2 ML/year).

Table 6 Surface water balance totals at Shannon Brook above Yorklea (model node CLM007). Results summarise the range in the 30 groundwater model runs for each of the three climate periods modelled in the Clarence‑Moreton bioregion

Three numbers are provided for surface water outflow. The first number is the median, and the 10th and 90th percentile numbers follow in brackets.

NM = data not modelled

Data: Bioregional Assessment Programme (Dataset 1, Dataset 2)

2.5.2.1.3 Water balance for Richmond River above Casino (model node CLM008)

The catchment area above model node CLM008 is 1874 km². The difference in the modelled water balance between the CRDP and the baseline for the Richmond River above Casino is in the surface water outflow over each of the three 30-year periods (Table 7). The difference was less than 0.05 GL for all three of the 30-year periods. Note that differences of less than 0.05 GL will appear as 0.0 GL in the table (0.05 GL over 30-year period is less than 2 ML/year).

Table 7 Surface water balance totals at Richmond River above Casino (model node CLM008). Results summarise the range in the 30 groundwater model runs for each of the three climate periods modelled in the Clarence‑Moreton bioregion

Three numbers are provided for surface water outflow. The first number is the median, and the 10th and 90th percentile numbers follow in brackets.

NM = data not modelled

Data: Bioregional Assessment Programme (Dataset 1, Dataset 2)

2.5.2.1.4 Water balance for Richmond River above Kyogle (model node CLM014)

The catchment area above model node CLM014 is 903 km2 and is upstream of the West Casino Gas Project extent. It has been included to check if there are any predicted impacts further north along the main Richmond river valley, beyond the West Casino Gas Project extent itself. The comparison of the modelled water balance between the CRDP and the baseline for the surface water outflow from the Richmond River above Kyogle shows that there is almost no difference for the 30-year period 2013 to 2042 (Table 8), and no increase in the subsequent two 30-year periods (Table 8). This indicates that there are no significant modelled changes in baseflow. Note that differences of <0.05 GL will appear as 0.0 GL in the table (0.05 GL over 30-year period is less than 2 ML/year). The results indicate that the groundwater drawdown due to the West Casino Gas Project does not propagate as far upstream as this catchment.

Table 8 Surface water balance totals at Richmond River above Kyogle (model node CLM014). Results summarise the range in the 30 groundwater model runs for each of the three climate periods modelled in the Clarence‑Moreton bioregion

Three numbers are provided for surface water outflow. The first number is the median, and the 10th and 90th percentile numbers follow in brackets.

NM = data not modelled

Data: Bioregional Assessment Programme (Dataset 1, Dataset 2)