1. Assistant Professor, Dept. of Civil and Environmental Engineering, Portland State Univ., P.O. Box 761-CEE, Portland, OR 97207 (corresponding author).
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Davis, CA 95616.
3. Design Engineer, Division of Safety of Dams, California Dept. of Water Resources, Sacramento, CA 94236-0001.