1. a Laboratory of Hydraulic Constructions (LCH) , Institute of Civil Engineering, Ecole polytechnique fédérale de Lausanne (EPFL) , Station 18, CH-1015 Lausanne, Switzerland (now at Basler & Hofmann West AG, Industriestrasse 1, CH-3052 Zollikofen, Switzerland) E-mail:
2. b Laboratory of Hydraulic Constructions (LCH) , Institute of Civil Engineering, Ecole polytechnique fédérale de Lausanne (EPFL) , Station 18, CH-1015 , Lausanne , Switzerland E-mail:
3. c Laboratory of Hydraulic Constructions (LCH) , Institute of Civil Engineering, Ecole polytechnique fédérale de Lausanne (EPFL) , Station 18, CH-1015 , Lausanne , Switzerland