Calibration of Density Driven Flow Model for the Freshwater Lens beneath the North Sea Island Borkum by Geophysical Data

With the aim to be able to estimate climate change impacts on coastal aquifers and especially the situation of barrier islands in the Wadden Sea a numerical model is set up for the North Sea island of Borkum. The work is done in the frame of the EU Interreg project CLIWAT. The database includes information from drillings, seismic measurements, an airborne electromagnetic survey (HEM) and monitoring data from two vertical electrode chains as well as measurements of groundwater table, pumping and slug tests, water samples. The groundwater model has been set up by the finite-element programme FEFLOW. The density driven flow model can be calibrated successfully on the base of hydraulic, hydrological and geophysical data. Verification runs with the calibrated model show a good agreement for the measured and computed hydraulic heads and the measured with computed TDS-data. This is the case as well on a large scale for the whole freshwater lens as also on a small scale in the area of the well fields.