1. Delft Hydraulics, Rivers, Navigation and Structures Division, P.O. Box 152, 8300 AD Emmeloord, The Netherlands
2. University of Twente, Department of Civil Engineering and Management, P.O. Box 217, 7500 AE Enschede, The Netherlands
3. International Institute for Hydraulic and Environmental Engineering, P.O. Box 3015, 2601 AD Delft, The Netherlands