1. Assistant Professor, Dept. of Soil and Water Conservation, National Chung Hsing Univ., 250 Guoguang Rd., Taichung 402, Taiwan (corresponding author).
2. Chair Professor, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan.
3. Graduate Student, Dept. of Civil Engineering, National Chiao Tung Univ., 1001 Ta Hsueh Rd., Hsinchu 300, Taiwan.
4. Graduate Student, Dept. of Soil and Water Conservation, National Chung Hsing Univ., 250 Guoguang Rd., Taichung 402, Taiwan.