Estimating daily recharge to the Chalk aquifer of southern England – a simple methodology

Abstract. A simple, practical model for estimating daily recharge - as hydrologically effective rainfall (HER) - to the Chalk outcrop of southern England is presented. Daily meteorological observations are the only data requirements. The model was calibrated for a Chalk river, the Wey, in south Dorset. Six different root constant thresholds were used to estimate daily actual evapotranspiration (AET) rates for the river. The model was then used to calculate HER using the six estimates of AET. Daily mean flow was simulated using three different models: CAPTAIN, IHACRES and INCA. The six HER estimates provided independent model inputs. HER calculated using a root constant of 200mm proved suitable not only for the Wey, but also (via a validation exercise) for other rivers on the Chalk of southern England for riverflow simulations as well as the timing and magnitude of groundwater recharge. The results suggest that a root constant of 200mm is optimal for the Chalk outcrop of southern England. The model is particularly useful for studies where the application of more complex methods of recharge estimation is impractical.

Keywords: Chalk aquifer, root constant, recharge, Hydrologically Effective Rainfall, model, riverflow, CAPTAIN, IHACRES, INCA, River Wey