2.6.2.4.2 Recharge

2.6.2.4.2.1 Analytic element model

Recharge was not included in the regional analytic element groundwater model (GW AEM). Recharge in no development, baseline coal resource development (baseline) and coal resource development pathway (CRDP) is the same. In this modelling approach, only the change in the system due to coal resource development is simulated. The change in recharge due to coal development is zero and therefore recharge is not included. A more detailed discussion on this rationale and the effect on predictions is provided in the qualitative uncertainty analysis in Section 2.6.2.8.

2.6.2.4.2.2 Alluvial MODFLOW models

Recharge to the alluvium is determined in two stages. Firstly, the target amount is determined from the observed salinity of the alluvium and stream and set as a fraction of monthly rainfall. After the Australian Water Resources Assessment Landscape model (AWRA-L) was fitted to the streamflow of the subcatchments, a monthly recharge distribution is extracted and scaled to the target values already used in fitting the MODFLOW model. The initial estimate was 20% of monthly rainfall applied to each stress period as recharge to alluvium. During the uncertainty analysis, this percentage is allowed to vary between 2% and 40% (see Section 2.6.2.8).

The fitting period was a 30-year interval from 1982 to 2011. The same 30-year interval was used for future climate runs, but recharge values were modified by seasonal scaling factors derived from global climate models (GCMs) as outlined in companion submethodology M06 (as listed in Table 1) for surface water modelling (Viney, 2016).