The variation of hydraulic conductivity with depth in the object-oriented groundwater model ZOOMQ3D

This report documents the implementation of the variation of hydraulic conductivity with depth within layers of the object-oriented regional groundwater model ZOOMQ3D. This representation of the vertical variation of hydraulic conductivity provides an alternative to the development of multi-layer models, in which individual layers are characterised by uniform horizontal hydraulic conductivity in the vertical direction. The approach has been developed to enable the more accurate description of the variation the hydraulic conductivity in limestone, and particularly Chalk aquifers, in which higher hydraulic conductivity values are often associated with the zone of fluctuation of the water table. The method circumvents numerical difficulties that are related to the de-watering of layers in multilayer models. The incorporation of the vertical variation of hydraulic conductivity with depth (VKD) mechanism has been rapidly incorporated into ZOOMQ3D due to the flexibility of the objectframework. The model has been rigorously tested by its comparison with a modified MODFLOW model (Environment Agency, 1999) in which VKD has also been implemented.