1. Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), Oryong-dong, Buk-gu, Gwangju 500-712, Korea, Korea Water Resources Corporation, Yeonchuk-dong, Daedeok-gu, Daejeon, Korea, and Hankuk Engineering Consultants Co., Kwachon, Kyungki-do, Korea