Modelling to support the assessment of interlinkages between groundwater and surface water in the context of the EU water framework directive

The EU Water Framework Directive (WFD) includes new common standards for an integrated assessment of entire hydrological systems at the catchment scale, implying among others, that water abstraction may not affect dependent ecosystems such as wetlands, lakes and water courses, nor the water quality of existing drinking water resources. Methods are needed to ensure that these requirements are fulfilled. To this end we developed and tested a procedure based on the application of results from a regional groundwater model for the whole county of Funen (Denmark) to investigate linkages between groundwater bodies (GWBs) and surface water, both under current and pristine conditions with respect to groundwater withdrawal. We found that discharge areas derived from the model application provide a good estimate for areas where GWB potentially may contribute to river runoff. For each GWB located at least partly within these areas, investigations have been performed whether or not hydraulic heads within some parts of the respective GWB are high enough to assume a contribution to river discharge. Additionally, median values of series of annual minima of daily river discharge measured at various locations along the main water courses in Funen County have been included in the investigations of groundwater/surface water interaction. The approaches applied are useful and repeatable for the regional basis analysis of the WFD, but require improvements, as discussed in the paper.