Model sequencing

For the numerical simulation of the hydrological changes due to additional coal resource development on the identified model nodes, a model or model sequence is needed that can simulate the impact on the regional groundwater system, the alluvial groundwater system and the stream network. Developing a single, coupled and integrated surface water and groundwater model is beyond the operational constraints and data available in this assessment. Therefore, for the surface water modelling of the Namoi subregion, a loosely coupled model sequence of three models was developed, consisting of a groundwater model MODFLOW-USG (see companion product 2.6.2 for the Namoi subregion (Janardhanan et al., 2018)) to simulate the resource development induced changes on the groundwater systems, and a rainfall-runoff model and a river routing and management model to simulate those changes on the surface water systems of the subregion.

Figure 3 shows in more detail the sequencing of the different models. The modelling is focused on the change in surface water statistics as a result of additional coal resource development, rather than on predicting future surface water flow under a given development pathway. The calibrated AWRA-L and AWRA-R models are used to determine the AWRA-L baseline and CRDP responses, respectively (see Section on model development for further details). The AWRA-R baseline and CRDP simulations are run using the results of the AWRA-L baseline and CRDP, respectively. The AWRA-R baseline run simulates streamflow at surface water model nodes incorporating the effects of commercially producing (as of 2012) open-cut coal mines. The AWRA-R CRDP run simulates streamflow at the surface water model nodes incorporating the effect of baseline coal mines plus the identified additional coal resource development.

Results of AWRA-R baseline are modified by the changes in baseflow caused by baseline coal mines in the groundwater model, whilst the results of AWRA-R CRDP are modified by the changes in baseflow by CRDP mines. The baseline and CRDP surface runoff results are used to calculate a number of hydrological response variables for both the baseline and CRDP. The change in hydrological response variables between the baseline and CRDP (due to the additional coal resource development) will inform where the receptor impact modelling is necessary for the surface water model nodes. A description of the surface water hydrological response variables (see Table 8) is provided in companion submethodology M06 (as listed in Table 1) for surface water modelling (Viney, 2016).

The technical detail of the conceptualisation, parameterisation and implementation, together with the uncertainty analysis of the simulated impacts, are documented in this product for the AWRA-L and AWRA-R models. Companion product 2.6.2 for the Namoi subregion (Janardhanan et al., 2018) describes the groundwater modelling methods.

Figure 3

Figure 3 Model sequence for the Namoi subregion

GW is the groundwater model as described in companion product 2.6.2 for the Namoi subregion (Janardhanan et al., 2018).

AWRA-L = Australian Water Resources Assessment landscape model; AWRA-R = AWRA river model; baseline = baseline coal resource development; CRDP = coal resource development pathway (the coal resource developments in the CRDP equal those in the baseline plus additional coal resource development); HRV = hydrological response variable; store Δ HRVs = storing of the changes in hydrological response variables

Last updated:
6 December 2018
Thumbnail of the Namoi subregion

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