1. Assistant Professor, Civil and Environmental System Engineering, Hanyang Univ., 1271 Sa-1 dong, Sangnok-gu, Ansan, Kyeonggi-do 425-791, Korea.
2. Professor and Head, Dept. of Civil Engineering and Engineering Mechanics, and Center for Sustainability of Semi-Arid Hydrology and Riparian Areas (SAHRA), Univ. of Arizona, Tucson, AZ 85721-0072.