Shallow Water : A comparison between hydraulic measurements and numerical models

In the near future hydropower will be used to regulate intermittent energy sources, shallow water ways can then occur in close proximity to the power plants, where the bottom often consists of stones in a similar length scale as the water depth. The idea of this project, which has been initiated by Vattenfall R\&D, is to compare experimental measurements in a laboratory environment with numerical simulations with CFD, this to find a way to represent roughness structures where there is low relative submergence. For the measurements in the lab, gravel were attached to the bottom of a flume and the water depth were measured for different flow rates and a CFD model were calibrated against the measurement data. A conversion of the Manning coefficient, originating from experimental measurements to equivalent Sand-grain size used in the CFD to model the roughness has been proposed and has shown good predictions of the maximum water depth. To capture the entire flow field, it is not enough to just model the friction from the roughness, it needs to be resolved and it may be necessary to consider the influence by form drag.