2.5.2.3 Gaps

Limitations lie in some parameters and the implementation of some stresses, such as localized discharge and evapotranspiration, in the groundwater model. Surface water relevant inputs, such as recharge and river stage, over the three reporting periods only reflect changes due to a single varying climate signal. Thus, the uncertainty in the climate signal is not taken into account in the current analysis. In order to improve model stability and reduce model runtime for a feasible sensitivity analysis, evapotranspiration was not explicitly simulated in the groundwater model. The estimated recharge component may compensate for the ignorance of evapotranspiration to some extent. Only the perennial reaches of the streams within the model domain were simulated directly using the River Package in MODFLOW. This simplification may underestimate stream recharge to the groundwater system. The dual-phase flow process near CSG wells was not modelled in the current project. Previous studies (Moore et al., 2013; Moore et al., 2014; Herckenrath et al., 2015) have shown that the omitting of dual-phase flow overestimates drawdown impact, especially for prediction near CSG wells, depending on hydraulic properties, development plans and simulation time. For example, Moore et al. (2015) reported a drawdown overproduction of 15 m at a distance of 7 km from the well extraction centre at a simulation time of 20 years within the targeted coal seam formation in their model. The Assessment team believe that storage change due to CSG development is also overestimated to some extent, although the impact on water balance analysis was not directly investigated in these studies. In addition, assumptions, limitations and gaps listed in companion products 2.6.1 (surface water numerical modelling) (Gilfedder et al., 2016) and 2.6.2 (groundwater numerical modelling) (Cui et al., 2016) for the Clarence‑Moreton bioregion also have an impact on water balance analysis.