User guide : BGS Conceptual Domains for Rapid Karstic Groundwater Flow in the Unsaturated Zone Dataset

There is now substantial evidence that the Chalk aquifer is impacted by karst (Maurice et al., 2021; Foley and Worthington, 2021; Farrant et al. 2021a,b). It is well known that in karst aquifers solutional development results in high vulnerability to pollution with the potential for rapid groundwater flow and long-distance pollutant transport. Karstic solutional development in the Chalk can lead to rapid groundwater flow through the unsaturated zone enabling the transport of pollutants from the surface to the saturated zone. In 2022 the British Geological Survey were commissioned by the Environment Agency to develop spatial domains using Geographical Information System (GIS) polygons that reflect the likelihood of rapid flow pathways within the unsaturated zone. This project was part of the wider Solent Shared Outcome Fund Project led by DEFRA to develop and test a land use change trading platform to help farmers and landowners manage their land better to reduce the potential for groundwater contamination. The Environment Agency are leading the mapping and modelling work stream of this project, which includes developing understanding of groundwater pathways and nitrate transport within the Solent catchment. The BGS part of the project led to the creation of four karst domains that range from a low to a very high likelihood that some fully connected rapid flowpaths are present in the unsaturated zone. The detailed methodology developed by BGS to create these domains is reported in Cullen-Gow et al. (2021), held by the Environment Agency. The aim of the current report is to provide some background on these domains and the factors used to create them, and further information on how they should be used and interpreted.