1. National Water Research Institute, Canada Centre for Inland Waters, Burlington, Ontario, L7R 4A6, Canada
2. CICESE, Departamento de Oceanografia Fisica, Km 107, Carretera TijuanaEnsenada, Ensenada B. C., México
3. Civil Engineering Department, Middle East Technical University, Ankara 06531, Turkey
4. Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, China