1. Ph.D. Student, Dept. of Civil and Environmental Engineering, Seoul National Univ., 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, South Korea.
2. Professor, Dept. of Civil and Environmental Engineering, Seoul National Univ., 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, South Korea (corresponding author).
3. Associate Professor, Dept. of Environmental Science and Engineering, Inje Univ., 607 Obang-dong, Gimhae, Gyungnam 621-749, South Korea.
4. Research Specialist, Hydro Science and Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology, Goyang-Si 10223, South Korea.