1. Research Assistant, Dept. of Civil Engineering, Univ. of Minnesota, Twin Cities, Saint Anthony Falls Laboratory, Mississippi River at 3rd Ave. S.E., Minneapolis, MN 55414 (corresponding author).
2. Professor, Dept. of Bioproducts and Biosystems Engineering, Univ. of Minnesota, Twin Cities, 1390 Eckles Ave., St. Paul, MN 55108.
3. Joseph T. & Rose S. Ling Professor and Head, Dept. of Civil Engineering, Univ. of Minnesota, Twin Cities, 500 Pillsbury Dr. S.E., Minneapolis, MN 55455.