Modelling the impact of forest cover on groundwater resources: A case study of the Sherwood Sandstone aquifer in the East Midlands, UK

Abstract

Land-use change from arable agriculture to forestry has become a focus in many European countries to control leaching of non-point agricultural pollutants such as nitrate to aquifers. However, a reduction in groundwater recharge beneath forest areas could potentially exacerbate water supply shortages. No direct study has previously been undertaken in the UK to assess the effect of increasing woodland cover on the quantity of groundwater resources. To address this knowledge gap, this study applied a groundwater flow model (MODFLOW) with a soil moisture balance recharge model to predict the effect of land-use change to forestry on groundwater recharge and levels by 2025 at two public supply borehole sites on the unconfined Sherwood Sandstone aquifer in Nottinghamshire. Four land-use change scenarios focusing on borehole capture zones were developed. The recharge calculations revealed a reduction of up to 45% in annual recharge as a result of an increase in woodland cover in the borehole capture zones, with the reduction more marked in winter than in summer at both borehole locations. However, the associated decrease in groundwater levels was limited owing to the high storage capacity of the sandstone aquifer. Even with an increase in woodland cover over the entire target zone, the simulated decrease in groundwater levels was less than 0.3 m. It is concluded that a quantitative analysis using a modelling approach can assist in the better targeting of pollution control strategies that include land-use change to woodland, helping decision-makers balance the expected improvements to groundwater quality while concurrently managing groundwater resources.