1. Water Resources Engineer, Center for Watershed Protection, 3290 North Ridge Rd., Suite 290, Ellicott City, MD 21043 (corresponding author).
2. Professor, Dept. of Biological and Agricultural Engineering, Kansas State Univ., 129 Seaton Hall, Manhattan, KS 66502.
3. Regents Professor, Dept. of Biosystems and Agricultural Engineering, Oklahoma State Univ., 111 Agricultural Hall, Stillwater, OK 74078.