1. Dept. of Civil and Environmental Engineering, Southern Illinois Univ. Carbondale, 1230 Lincoln Dr., MC 6603, Carbondale, IL 62901 (corresponding author).
2. Dept. of Civil and Environmental Engineering and Dept. of Geology, Univ. of Illinois at Urbana-Champaign, Hydrosystems Laboratory, MC 250, 205 N. Matthews Ave., Urbana, IL 61801.