1. Dep. of Agroecology, Faculty of Science and Technology; Aarhus Univ.; Blichers Alle 20, P.O. Box 50 DK-8830 Tjele Denmark
2. Dep. of Civil Engineering; Aalborg Univ.; Sohngaardsholmsvej 57 DK-9000 Aalborg Denmark
3. Dep. of Hydrology and Water Resources; Arizona Univ.; 1133 E. James E. Rogers Way, P.O. Box 210011 Tucson AZ 85721-0011