1. Research Associate and Group Leader, Environmental Fluid Mechanics Group, Institute for Hydromechanics, Univ. of Karlsruhe, D-76128 Karlsruhe, Germany (corresponding author).
2. Assistant Professor, Zachry Dept. of Civil Engineering, Texas A and M Univ., 3136 TAMU, College Station, TX 77843-3136.
3. Professor and Head, Institute for Hydromechanics, Univ. of Karlsruhe, D-76128 Karlsruhe, Germany.