1. a Formerly Institute for Hydromechanics, Karlsruhe Institute of Technology (KIT) , D-76128, Karlsruhe, Germany E-mail:
2. b Laboratory of Hydraulics, Hydrology and Glaciology (VAW) , ETH Zurich , 8092, Zurich, Switzerland
3. c Institute for Soil Mechanics and Rock Mechanics, Karlsruhe Institute of Technology (KIT) , D-76128, Karlsruhe, Germany E-mail: