1. Engineering Research Center, Colorado State Univ., Fort Collins, CO 80523.
2. Delft Hydraulics and IHE, P.O. Box 177, 2600 MH Delft, The Netherlands.
3. National Institute for Inland Water Management and Waste Water Treatment, RIZA, P.O. Box 9072, 6800 ED Arnhem, The Netherlands.
4. Dept. of Physics Geography, Utrecht Univ., P.O. Box 80115, 3508 TC Utrecht, The Netherlands.