Groundwater recharge to a fractured limestone aquifer overlain by glacial till in County Monaghan, Ireland

Abstract

Obstractions from the Knockatallon aquifer in County Monaghan, Ireland, caused groundwater levels to fall substantially over a 20 year period. The aquifer consists of two formations of fractured limestone and other Carboniferous rocks. The aquifer is overlain by up to 53 m of low-permeability glacial tills. The presence of this overburden inhibits direct recharge to the aquifer. Recharge was investigated using a combination of approaches: soil moisture budget, water balance, environmental tracers, through flow analysis and river baseflow analysis. The study showed that the proportion of effective rainfall that replenishes the aquifer as direct recharge through the till is very low (less than 5%), and thus that the presence of the till has a major impact on recharge. The study also highlighted the importance of applying several approaches when trying to quantify recharge, as any single approach on its own is unlikely to give satisfactory results.