Author(s): Christian Noss; Kaan Koca; Peggy Zinke; Pierre-Yves Henry; Christy Ushanth Navaratnam; Jochen Aberle; Andreas Lorke
Keywords: Field studies; gravity waves; laboratory studies; open channel flow turbulence; streams and rivers
Abstract: Water surface roughness in rivers and streams is mainly driven by flow, turbulence and riverbed conditions. Conversely, water surface roughness gives easy access to information about hydrodynamics – provided that measurements are possible at sufficient spatial-temporal resolution and accuracy. We present a novel small-size (diameter 28 mm) drifter, which detects water surface roughness through acceleration measurements while floating on the water surface. Laboratory tests revealed a good agreement between drifter-based measurements and optical characterization of surface roughness. Only very short waves with periods <0.15 s remained undetected by the drifter. Results from laboratory and field experiments show strong correlations between the drifter-measured water surface roughness, flow and shear velocities, Froude and Reynolds numbers. The small-sized drifter is particularly appropriate for reach-scale measurements in streams, where the application of other devices or methods is too large or laborious.