1. Ph.D. Student, Dept. of Biological and Agricultural Engineering, Texas A&M Univ., P.O. Box 2117 TAMU, College Station, TX 77843.
2. Assistant Professor, Dept. of Irrigation and Reclamation Engineering, Univ. College of Agriculture and Natural Resources, Univ. of Tehran, P.O. Box 4111, Karaj, 31587-77871 Tehran, Iran (corresponding author).