1. Ph.D. Student, State Key Laboratory of Hydroscience and Engineering, Tsinghua Univ., Beijing 100084, P R China.
2. Professor, State Key Laboratory of Hydroscience and Engineering, Tsinghua Univ., Beijing 100084, P R China. (corresponding author).
3. Senior Engineer, China Three Gorges Corporation, Chengdu 610041, P R China.
4. Engineer, Beijing Urban Construction Design & Development Group Co. Limited, Beijing 100037, P R China.