1. Research Hydraulic Engineer, U.S. Dept. of Agriculture, Agricultural Research Service, U.S. Arid Land Agricultural Research Center, 21881 N. Cardon Lane, Maricopa, AZ 85138 (corresponding author).
2. Professor Emeritus, Dept. of Soil, Water and Environmental Sciences, Univ. of Arizona, Tucson, AZ 85721.
3. Research Hydraulic Engineer, U.S. Dept. of Agriculture, Agricultural Research Service, U.S. Arid Land Agricultural Research Center, 21881 N. Cardon Lane, Maricopa, AZ 85138.