2.5.2 The water balances


Hydrological changes due to coal resource development in the Namoi subregion are summarised in the form of water balances. Separate summaries are provided for groundwater and surface water; however, the streamflow term in the surface water balances includes a contribution from the groundwater model.

The groundwater balance covers the entire groundwater modelling domain. The key water balance term for the coal resource developments is the extractions for coal mining and coal seam gas (CSG) operations (this includes both deliberate and induced take). The reported values are based on mean annual extraction rates over each 30-year period and vary between simulations due to the parameter differences. Between 2013 and 2042, the increase in the median 30-year mean annual pumping rate due to additional coal resource development is 9.1 GL/year which is more than an order of magnitude greater than the baseline rate of 0.2 GL/year (but still very small (<3%) compared to the total licensed extractions of 316 GL/year). Between 2043 and 2072, all baseline developments cease, but there is a comparatively small amount of mine and CSG extractions (i.e. 30-year mean of 2.9 GL/year) for additional coal resource development. The modelled surface water – groundwater flux response to mine water pumping and hydraulic enhancement is a decreasing trend in river losses to groundwater over the three 30-year periods. The additional coal resource development results in losses of streamflow of 3.5 GL/year in the 2013 to 2042 period, 2.1 GL/year between 2043 and 2072, and 0.6 GL/year between 2073 and 2102. These additional losses are small compared to the trend in increasing stream losses through time in the baseline due to licensed extractions (40.7 GL/y for 2013 to 2042 up to 62 GL/y for 2073 to 2102).

The water balance at model node 13 on the Namoi River (Namoi River at Mollee) with a contributing catchment area of 26,534 km2 shows less than 1% change in the streamflow between baseline and coal resource development pathway (CRDP) for all periods.

Although the changes in the water balance components are small, changes in other hydrological response variables may be significant (e.g. drawdown or no-flow days). These other metrics are reported in companion product 2.6.1 (Aryal et al., 2018) and companion product 2.6.2 (Janardhanan et al., 2018) for the Namoi subregion.

Last updated:
17 December 2018