Catchment-scale water balance modelling in a Carboniferous Limestone aquifer

Abstract

AbstractGroundwater models are used to manage water resources in carbonate aquifers throughout the UK. These models often utilize non-linear modifications of equivalent porous media (EPM) assumptions to simulate the observed head-flow relationships. This paper describes the application of similar principles to time-variant water balance modelling of a karstified aquifer: the Carboniferous Limestone in SW England. The non-linear model successfully simulates the large changes in bulk hydraulic conductivity required to adequately model flows from two karstic spring catchments. Model results illustrate that the rate of drainage from the vadose zone is affected by the extent and thickness of soil cover. In a catchment with mixed soil cover, vadose zone drainage is shown not to be significant in sustaining summer low flows at the spring. The performance of the model is limited in some cases: summer storm flows in particular are poorly simulated. The limitations suggest that the true response of the system is dependent on recharge intensity (rate) as well as antecedent water levels and that the EPM assumption of good connection between conduits and the diffuse flow zone is not always valid in this aquifer. This may have implications for groundwater model design in other carbonate aquifers.