1. Assistant Professor, Dept. of Natural Resources Conservation, Univ. of Massachusetts, Amherst, 160 Holdsworth Way, Amherst, MA 01003-9285 (corresponding author).
2. Professor, Dept. of Civil Engineering, FH Wiesbaden, Univ. of Applied Sciences, Kurt-Schumacher-Ring 18, 65197 Wiesbaden, Germany.
3. Research Assistant, Dept. of Natural Resources Conservation, Univ. of Massachusetts, Amherst, 160 Holdsworth Way, Amherst, MA 01003-9285.