1. Hydraulic Engineer, U.S. Dept. of the Interior, Bureau of Reclamation, Water Resources Research Laboratory, Denver, CO. E-mail: twahl@do.usbr.gov
2. Research Leader and Research Hydraulic Engineer, USDA-ARS, U.S. Arid Land Agricultural Research Center, Maricopa, AZ.
3. Research Hydraulic Engineer/Collaborator, USDA-ARS, U.S. Arid Land Agricultural Research Center, Maricopa, AZ.
4. Professor, International Institute for Geo-Information Science and Earth Observation/ITC, The Netherlands.