1. MIT/WHOI Joint Program in Oceanography, Mail Stop 8, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543-1050, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 48-321, Cambridge, Massachusetts 02139, and Flow Visualization and Processes Laboratory, Geohydrology Department, Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 37185-0735