Investigating the impacts of low permeability layers in the Chalk on groundwater levels and river flows using multiple modelling methods : lessons from the Ver catchment

In northwest Hertfordshire, the Chalk stratigraphy comprises of the New Pit Formation with numerous marl bands. At the base of the underlying Hollywell Nodular is the Melbourn Rock and the Plenus Marls Member. These marl bands are characterized as low hydraulic conductivity horizons and can “split" the aquifer and control its response to perturbations such as recharge and abstraction. In this study we apply numerical modelling to site data of the Chalk aquifer near the River Ver to explore how these various low permeability marl layers might affect Chalk stream baseflow in response to changes in groundwater abstraction. Groundwater in southeast England supports a large proportion of public water supply and sensitive ecosystems. A significant proportion of this groundwater comes from the Chalk aquifer. The Government’s 25-Year Environment Plan highlights the importance of restoring flow to ecologically important chalk streams. Here we demonstrate the importance of multi layer settings of hydrogeological models to improve the management of water resources and protect England’s rare chalk streams.