D - Depth to water table (DRASTIC)

The D layer is the depth to the water table from the surface. The Rockingham study area is based on 120 historical water level data points along with spring data and data from groundwater surface water interactions. Spatial interpolation using kriging was used and then the values were classified into the D index values. The highest D values correspond to where the water table is shallowest, generally found in the lower areas in the catchment, with the lowest D values meaning greater depth to the watertable, found in the upland areas. The water table is generally very shallow, with much of the area having depths to water of less than 3 m bgl. The elevated karst plateau to the south has the deepest water with depths to water of up to 40 m.