1. Assistant Research Professor, Division of Hydrologic Science, Desert Research Institute, 755 E. Flamingo Rd., Las Vegas, NV 89119 (corresponding author). E-mail: dchen@dri.edu
2. Assistant Professor, Dept. of Civil Engineering and Engineering Mechanics, The University of Arizona, 1209 E. 2nd St., Room 324E, Tucson, AZ 85721. E-mail: gduan@email.arizona.edu