The Dumfries Basin in Scotland is a regionally significant aquifer that provides water for public supply, industry, agriculture and private consumption. Whilst a significant amount of water is brought onto the basin as river flow, the groundwater resource is difficult to quantify because of the complex nature of the Quaternary deposits that overlie the Permian sandstone and breccia aquifer. The heterogeneity of the superficial fluvio-glacial clays, sands and gravels means that recharge is difficult to assess and riveraquifer interaction is understood poorly. Furthermore, improvement of the conceptual model of surface water-groundwater interaction has been hindered by the paucity of monitored flow data along the river channels.
By simulating the response to test pumping of three boreholes, drilled in a
line perpendicular to the River Nith, the largest river in the basin, a detailed
conceptual model of groundwater flow at the local scale has been developed.
The development and refinement of the numerical model benefited significantly
from the collection of data associated with the response of the groundwater
levels to a river flood peak, which passed down the River Nith during the test.
The test was simulated using the ZOOMQ3D code, which enabled local grid refinement
of the 500 m square base mesh to 0.2 m square cells around the boreholes. Consequently,
both the linear river and radial flow to the boreholes could be represented
accurately.