Derivation of a Methodology for Groundwater Recharge Assessment in Scotland and Northern Ireland
Key Words: Groundwater, Recharge, Water Framework Directive
- Recharge estimation is an important component in the assessment of the quantitative stresses. A summary of the environmental influences on recharge processes in Scotland and Northern Ireland is presented in the report and it is highlighted how these differ from the rest of the UK. The key recharge environments are summarised.
- Consultation was undertaken with relevant UK and Irish organisations and an assessment of recharge estimation methodologies made. A methodology for enabling efficient assessment of recharge to each groundwater body in Scotland and Northern Ireland is proposed.
- This methodology is based on a water budget approach which estimates direct and indirect recharge flow components. This includes estimation of effective rainfall, actual evapotranspiration and run-off in addition to the potential impacts of snow-melt, bypass flows, urban recharge and surface water leakage.
- Three levels of complexity in the estimation of recharge are proposed dependent on the perceived risk of quantitative stress to the groundwater body. The recommended complexity increases from a monthly calculation of the flow components through to daily timesteps and up to a distributed recharge and groundwater flow model.
- A software tool to assist in the recharge estimation for the lower two levels of complexity has been developed in Microsoft Excel. This guides the user on the input of required parameters. The report has been constructed to assist the user in determination of the required input parameters.
- Recommendations for future work including validation of the recharge model and further interpretation of the link of soil mapping with surface run-off and interflow are made.
- The error of uncertainty in the recharge estimation increases with the scarcity of data available to the groundwater body. Many areas in Scotland and Northern Ireland will rely on national mapping of climatic, landuse, soil and aquifer properties. It is important that the confidence in the recharge estimation is balanced against the perceived risk of stress to the groundwater body.
- It is likely that in areas of poor data coverage that the error of uncertainty in the calculation could be +/- 100%. Given this uncertainty, where the range of possible actual recharge is within a factor of 2 over the groundwater body compared to the abstraction volume, then further assessment of the quantitative pressures is recommended.
Copies of this reports are available from the Foundation, price £35.00, less 20% to FWR members.
N.B. The report is available for download from the SNIFFER Website