Turbulence measurements in shallow flows in gravel-bed rivers

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732Input from actual field measurements is required by river modelers in order to improve turbulence equation closures in hydrodynamic models. This paper is based on 3D ADVP river measurements taken in a gravel-bed river under shallow and stationary flow conditions. The blockage ratio is h/D503.0. It was found that the flow depth can be divided into three inviscid layers: roughness layer (z0.80h). The turbulence distribution was measured and analyzed including all the components of the Reynolds stress tensor (RST). The streamwise turbulent intensity dominates the TKE, representing between 50 to 80% of the TKE. Spanwise and vertical contributions throughout the flow depth are analyzed as well. A comparison of the results with empirical formulas given by previous authors to describe normal RST components shows their limitations in the roughness layer of the flow. In the roughness layer, RST shear stresses other than the longitudinal acquire more importance and occasionally prevail. In the intermediate layer, the flow is 2D and the velocity distribution is mainly logarithmic. Here, the longitudinal Reynolds shear stress distribution is linear and self-similar; the influence of bed roughness and surface irregularities is smoothed out and a combined shear effect is exerted