Groundwater models for water resources assessment at regional, local and site scales

For 25 years, the UK’s Environment Agency has commissioned groundwater flow models of the main aquifers in England. These regional-scale models are regularly updated, occasionally recalibrated and used for water resources management, regulatory decisions and impact assessment of groundwater abstractions. This range of uses requires consideration of the appropriate scale of data collection and modelling and adaptation of the groundwater models, with refinement where local impacts on individual springs and seasonal streams are considered and combination and simplification for strategic national water resources planning. The Cretaceous Chalk, a soft white limestone, is the major aquifer of southern and eastern England, supplying up to 80% of the drinking water in this densely populated region. Springs and baseflow of good quality groundwater feed Chalk streams, which are a rare and valuable habitat with a high public profile, but face significant challenges in the 21st century, worsened by climate change and population growth. The modelling informs strategic planning and regulatory decisions, but the model’s scale needs to be appropriate for each issue. The presentation defines these issues and presents examples, ranging from the large-scale, strategic Water Resources East to impact assessment for individual groundwater abstractions and more bespoke local investigations, including simulation of groundwater flood risks. As the scale of investigations reduces, there is increasing importance on the accuracy of information, both temporally and spatially. Model refinement made during local investigations can be incorporated into larger-scale models to ensure that this understanding is captured.