Coupling a radial model of the Darcy-Forchheimer equation with a regional groundwater model to simulate drawdown at supply boreholes

Assessing the short and long-term risks to a groundwater source is a critical part of water resource management. In the UK, public water supply companies apply the term Deployable Output (DO) to describe the yield of a groundwater source under drought conditions. DO is constrained by the physical properties of an aquifer and operational factors such as licence conditions, water quality, and pumping and treatment capacity. A robust assessment of groundwater DO should be informed by numerical modeling. This requires the groundwater level in a supply borehole to be accurately simulated within its regional hydrogeological context. A 3D radial flow model of the Darcy-Forchheimer equation is presented for simulating drawdown at a borehole. The Darcy-Forchheimer Radial Flow Model (DFRFM) represents linear and non-linear flows around the borehole; confined and unconfined conditions; vertical heterogeneity in the aquifer and borehole storage. The DFRFM is coupled with a regional groundwater model which represents the large-scale groundwater system, including lateral and vertical aquifer heterogeneity, rivers, and spatially varying recharge. The model has been applied to a supply borehole located in the dual permeability Chalk aquifer, which forms the principal aquifer in the UK and provides 40-70% of the total public water supply in southern and eastern England. The application demonstrates the potential for the coupled model to be used to inform DO assessments and to assess the long-term risk to sources under climate change scenarios.