SENSITIVITY TESTING OF THE METHODOLOGY FOR GROUNDWATER RECHARGE ASSESSMENT

SENSITIVITY TESTING OF THE METHODOLOGY FOR GROUNDWATER RECHARGE ASSESSMENT
WFD31
March 2004

EXECUTIVE SUMMARY

Initial estimations of recharge using the tool developed by Entec have indicated an over estimation of recharge in areas of high effective precipitation and low aquifer storage and transmissivity. The applicability of bypass flows and interflow to the calculations is considered important.
Further clarification has been provided concerning the relationship between HOST and surface runoff and the subdivision of surface runoff and interflow. HOST applies to the soil hydrological properties and is related to surface runoff from within the soil zone. Interflow relates to the hydrological properties of the subsoil and the underlying groundwater body.
A calculation of interflow based on the application of a limit to the actual recharge has been proposed.
It is proposed that inclusion of bypass flows is restricted to groundwater bodies which are identified as being at risk of failure to achieve quantitative good status. The values used should be linked into further characterisation and field estimation of the parameters.
Initial sensitivity testing of the recharge calculation to these input flows was conducted to determine the confidence that can be ascribed to an individual groundwater body recharge estimation.
The spreadsheet has been developed to include the above changes and expanded to allow calculations on up to three aquifer types within a groundwater body. An update of the Entec spreadsheet incorporating these changes is included with this report.

KEY WORDS Groundwater, Recharge, Water Framework Directive

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