1. Department of Environmental Science, Institute for Water and Wetland Research, Radboud University Nijmegen, 6500 GL Nijmegen, the Netherlands
2. Flanders Environment Agency (VMM), Dr. De Moorstraat 24-26, B-9300 Aalst, Belgium
3. Unit Soil and Subsurface Systems, Deltares, P. O. Box 85467, 3508 AL Utrecht, the Netherlands