2.6.2.7 Observations and predictions

Summary

The regional analytic element groundwater model (GW AEM) and the Avon and Karuah MODFLOW models are designed to predict the maximum difference in drawdown (dmax) for one realisation within an ensemble of groundwater modelling runs, obtained by choosing the maximum of the time series of differences between two futures, and time to this maximum change (tmax) at the groundwater receptors in the surface weathered and fractured rock layer and the alluvial aquifers respectively.

In the design of experiment, ten thousand parameter combinations, generated through a Latin Hypercube sampling, are evaluated to provide a training set for the emulators that are used in the uncertainty analysis.

The sensitivity analysis based on these runs indicate that dmax and tmax for both the analytic element and the alluvial models are most sensitive to the hydraulic properties of the weathered zone. In addition to that, the drainage flux in the Avon MODFLOW model is most sensitive to the hydraulic conductivity of the alluvium and the riverbed conductance, while in the Karuah MODFLOW model the drainage flux is most sensitive to the recharge multiplier.

The exchange flux with the deeper sedimentary basin is for both the Avon and Karuah MODFLOW models most sensitive to the hydraulic conductivity of the weathered zone and the constant head offset.