1. Assistant Professor, Dept. of Water Environment and Civil Engineering, Shinsyu Univ., 4-17-1 Wakasato, Nagano 380-8553, Japan; formerly, Ph.D. Student, Dept. of Civil and Environmental Engineering, Hiroshima Univ., 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan.
2. Assistant Professor, Dept. of Civil and Environmental Engineering, Hiroshima Univ., 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan (corresponding author).
3. Professor, Dept. of Civil and Environmental Engineering, Tohoku Gakuin Univ., 13-1 Chuou 1, Tagajo, Miyagi 985-8537, Japan.