1. U.S. Geological Survey, Washington Water Science Center; Tacoma Washington USA
2. Now at Department of Civil, Environmental, and Geo- Engineering, St. Anthony Falls Laboratory, and National Center for Earth-surface Dynamics; University of Minnesota; Minneapolis Minnesota USA
3. U.S. Geological Survey, Illinois Water Science Center; Urbana Illinois USA
4. U.S. Geological Survey, Georgia Water Science Center; Norcross Georgia USA