1. Member, ASCE
2. Consulting Engr., Parsons Engineering Science, 290 Elwood Davis Rd., Ste. 312, Liverpool, NY 13088.
3. Assoc. Prof., Dept. of Civ. and Envir. Engrg., Univ. of Massachusetts, Amherst, MA 01003 (corresponding author). E-mail: ergas@ecs.umass. edu