AbstractThe Chalk is a principal aquifer which provides an important resource in SE England. For two centuries, it allowed the establishment of a thriving watercress-growing industry, indirectly through diverted stream flow and directly through the drilling of flowing artesian boreholes. The distribution of artesian boreholes across different catchments, suggests a regional control of vertical groundwater flow within the New Pit and Lewes Chalk units. Interrogation of location-specific information points to the confining role of a few key marls within the New Pit Chalk Formation, which can be traced up-catchment to where they naturally outcrop or have been exposed by quarrying. Evidence is found in geophysical logging of a number of boreholes across catchments, confirming a consistent pattern of the spatial distribution of such key markers. When tectonic stress was applied to the various Chalk formations, the marl bands would have reacted, producing more plastic deformation and less fractures in comparison with rigid rock strata. Such a scenario would have created the conditions for secondary aquifer units, giving the Chalk confining or semi-confining hydraulic characteristics on a regional scale. This conceptual understanding helps explain why the river flow response to reductions in groundwater abstraction varies across the flow duration curve.