The Namoi subregion groundwater model is developed in MODFLOW-USG to probabilistically assess the drawdown due to additional coal resource development, and the year of maximum change, as well as to provide the change in surface water – groundwater flux as a boundary condition for the surface water modelling reported in companion product 2.6.1 for the Namoi subregion (Aryal et al., 2018).

Model results indicate that the probability of exceeding a 0.2 m drawdown close to the mine footprint areas is high, but this reduces with increasing distance from the development. The contour of 5% probability of exceeding 0.2 m drawdown is generally within 10 km of the development footprint boundary.

The year when maximum change is attained varies throughout the Namoi subregion. It is most likely to be during the decades after mining activity ceases, and it increases with increasing distance from mine tenements.

The Namoi subregion groundwater model is a stochastic regional-scale model: it has a large modelling domain and a relatively coarse model resolution. As such, it does not provide a deterministic result and it does not incorporate the level of lithological and hydrogeological information that is represented in local-scale groundwater models that have been built for small areas within the Namoi subregion.

Opportunities to improve the model can be directed to better constraining the assumptions that have the most influence on model results. Generally, the magnitude of drawdown due to additional coal resource development, which is the difference in drawdown between the coal resource development pathway and baseline, is most sensitive to the hydraulic properties of the interburden and coal-bearing formations.

Last updated:
6 December 2018
Thumbnail of the Namoi subregion

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