Translation of the Doncaster Groundwater Model into the MODFLOW code

This report documents the translation of the Doncaster groundwater model, originally developed by the University of Birmingham, into a MODFLOW code (McDonald and Harbaugh, 1988) to be used within the AISUWRS (Assessing and Improving Sustainability of Urban Water Resources and Systems) project (Morris et al., 2003). The Doncaster model (hereafter referred to as the original model) was established in 1993 by I.T. Brown and K.R. Rushton from the University of Birmingham (Brown and Rushton, 1993). It was extended and slightly modified in 1997 by M. Shepley of the Environment Agency (Shepley, 2000). The original model is regarded as a well-calibrated regional groundwater model, which adequately represents the aquifer conditions in the Doncaster area. It was therefore selected as the basis of the groundwater model to be used within the AISUWRS project. A translation of the original model code into MODFLOW code was deemed necessary in order to simulate both solute transport and groundwater flow. It also provides flexibility to change model input parameters for scenario modelling without recourse to the Environment Agency. A major aim of the AISUWRS project is to simulate various urban water resources management options. The regional MODFLOW model will form the basis for a future sub-regional model, focused on Bessacarr, a suburb of Doncaster, which is the centre of investigations within the AISUWRS project. The report is written in six sections. Section one presents set up and discretization of both models. Section two describes the representation of aquifer parameters, while section three comments on the representation of external and internal boundaries. Section four discusses initial conditions and section five summarises the discretization of time in both models. The output of the Modflow model and the comparison with the original model outputs is given in section six. This report details only the conversion of the original model into a MODFLOW equivalent. No detailed description of the original model itself is presented, as this is outside the scope of this report. For an in depth description of the conceptual model behind the original numerical model, the methods used to derive aquifer parameters, the way recharge values were established, etc. the reader is referred to Brown and Rushton (1993) and Shepley (2000).