1. Department of Environmental Science and Engineering, Oregon Graduate Institute, P.O. Box 91000, Portland, Oregon 97291-1000, Department of Civil Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1, U.S. Geological Survey, Water Resources Division, 810 Bear Tavern Road, West Trenton, New Jersey 08628, and U.S. Geological Survey, Water Resources Division, 1608 Mt. View Road, Rapid City, South Dakota 57702