Challenges of modelling a complex multi-aquifer groundwater system at a national scale: case study from the UK

Modelling of the UK groundwater system, composed of multiple discrete aquifers, is undertaken to help assess water resources at the national scale. This groundwater system is made of the major aquifers that overlie each other in some places but which are nonetheless not in a hydraulic contact, and the minor aquifers formed in the superficial deposits. While the major aquifers are not in the direct contact, they are linked by the river network and may exchange water thanks to the aquifer-river interaction processes. In this paper we present a numerical model of this complex system, which is not as demanding to build and run as a fully distributed multi-layered model. The model represents the three most important UK aquifers: Chalk, Jurassic Limestone, and Permo-Triassic Sandstone as separate layers discretized using square buckets that are connected horizontally. These layers are connected to the river network and receive recharge through the buckets that represent their outcrops. An extra layer is also added to represent the minor and non-aquifers. The model was tested at 37 gauging stations distributed across the country. Good fit to the observations was obtained in the steady state run. Further work will include incorporation of abstractions and additional model refinement to represent spatial heterogeneity.