Application of a parsimonious large-scale distributed groundwater flow model to quantify inter-catchment groundwater flow

Inter-catchment groundwater flow (IGF) is important in water resources management because it can affect the quantity and quality of freshwater by connecting topographically separated catchments through the subsurface. Traditional measurements of rainfall, evapotranspiration, and runoff can provide indications of IGF through catchment-scale mass balance analysis. However, it is difficult to study the detailed space-time variability of IGF using measurements only. Current rainfall-runoff models often either neglect IGF completely or include an over-simplified representation disregarding the spatial variability of IGF. Three-dimensional groundwater flow models can simulate the space-time variability of IGF, although they require a substantial amount of data and computational resources. In comparison, a two-dimensional model that simulates groundwater flow only horizontally considering depth-averaged hydrogeological properties, demands significantly less subsurface data and computational resources. This study evaluates the performance of a two-dimensional groundwater flow model in simulating IGF across the topographic boundaries of two chalk catchments located in the South of England. We demonstrate that our proposed model, using publicly available data, simulates the space-time variability of IGF and closes the mass balance within the topographic catchment boundaries consistent with observations. We find that a topographic catchment can lose 19% of its annual precipitation as IGF, supporting the needs for including the space-time variability of IGF in freshwater management.