The use of aero-magnetics to enhance a numerical groundwater model of the Lagan Valley Aquifer, Northern Ireland

Numerical modelling of aquifers is a standard process in the sustainable management of groundwater resources. To be reliable, a groundwater model requires an accurate geological framework, particularly where structure is complex. The Lagan Valley aquifer near Belfast is an example of an otherwise generally homogenous sandstone aquifer intruded by extensive swarms of low-permeability igneous dykes. The dissection of the aquifer by these dykes affects groundwater flow direction and borehole yield. We have used the Tellus aeromagnetic data to map the extent of these dykes and so improve the geometrical parameterisation of the models. Two methods are described for incorporating the effect of the dykes: a visual deterministic approach and a stochastic approach using Multiple Point Statistics. Both approaches resulted in models that significantly improved matches to observed groundwater levels and flow directions, demonstrating the value of aero-magnetic data for constraining these models.