1. Postdoctoral Fellow, Oak Ridge Associated Universities, sponsored by Conservation and Production Research Lab., USDA-ARS, P.O. Drawer 10, Bushland, TX 79102; formerly, Graduate Research Assistant, Dept. of Agricultural and Biosystems Engineering, Univ. of Arizona, Tucson, AZ 85721.
2. Professor, Dept. of Biological Systems Engineering, Univ. of Wisconsin, Madison, WI 53706 (corresponding author).
3. Professor, Dept. of Civil Engineering and Engineering Mechanics, Univ. of Arizona, Tucson, AZ 85721.
4. Postdoctoral Research Associate, Dept. of Civil Engineering and Engineering Mechanics, Univ. of Arizona, Tucson, AZ 85721.