1. Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of California, Los Angeles, CA 90095-1593.
2. Research Hydrologist, California Water Science Center, San Diego Project Office, U.S. Geological Survey, 4165 Spruance Rd., Suite 200, San Diego, CA 92101.
3. Distinguished Professor, Dept. of Civil and Environmental Engineering, Univ. of California, Los Angeles, CA 90095-1593 (corresponding author).