Modelling the Vale of St Albans: parameter estimation and dual storage
Published:January 01, 2012
A. B. Taylor, N. A. Martin, E. Everard, T. J. Kelly, 2012. "Modelling the Vale of St Albans: parameter estimation and dual storage", Groundwater Resources Modelling: A Case Study from the UK, M. G. Shepley, M. I. Whiteman, P. J. Hulme, M. W. Grout
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The development of the Vale of St Albans groundwater model made use of two techniques not commonly used in UK regional modelling studies: parameter estimation (using PEST) and representation of dual storage. Parameter estimation techniques can significantly improve model calibration and can be used to inform model development. Because parameter estimation typically involves running a groundwater model many hundreds of times, using a steady-state version of the model can help to keep run times short. Care must be taken to ensure that the parameter distributions produced through these techniques are conceptually defensible, and they must be checked against the conceptual model and modified where necessary. Simulation of extreme conditions such as floods and droughts can be problematic for Chalk aquifers. Previous studies have shown that the Chalk can be resistant to drought, with higher flows recorded in rivers than can be accounted for from releases from fissure storage alone. An approach has been developed that simulates a weak hydraulic connection between fissures and a proportion of matrix storage within the Chalk, providing a delayed yield of significant additional volumes of water during droughts. The application of this approach results in a significant improvement in the simulation of extreme events.
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Groundwater Resources Modelling: A Case Study from the UK
The UK is a country with over 150 years of widespread exploitation of its principal aquifers for public water supply. Increasing demands, greater awareness of environmental pressures and more exacting legislation has heightened the need for quantitative models to predict the impacts of groundwater use. In the UK this has culminated in a unique national, regulator-led programme for England and Wales to develop conceptual and numerical models of the principal bedrock aquifers.
The outcomes of this programme will be of interest to the international hydrogeological community, particularly as international legislation such as the European Water Framework Directive requires management of water issues across administrative boundaries with a varied cast of stakeholders.
The collection of papers provides a contrast between practitioner- and research-based approaches to assess and predict the anthropogenic impacts and environmental pressures. Many insights are provided on how the regular use of groundwater models may address the environmental challenges of the future.