1. Center for Applied Geoscience (ZAG), Eberhard-Karls University of Tuebingen, Sigwartstr. 10, D-72076 Tuebingen, Germany, Department of Civil Engineering & Canadian Rivers Institute, University of New Brunswick, Fredericton NB, Canada, and CSIRO Land and Water, Private Bag No. 5, Wembley WA 6913, Australia