1. Professor, State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan Univ., Chengdu, Sichuan 610065, P.R. China. E-mail: liao@msu.edu
2. Professor, Dept. of Civil Engineering, The Univ. of Birmingham, Edgbaston, Birmingham B15 2TT, U.K. (corresponding author). E-mail d.w.knight@bham.ac.uk