Entropy parameter estimation in large-scale roughness open channel

The entropy model allows estimating, in an expeditive way, both water discharge and flow velocity field in open channels. In fact, such model presents an almost simple analytical structure, based on the evaluation of a single parameter calculated through the ratio between the mean and maximum flow velocities in the cross section. Recent studies have demonstrated that, for large-scale roughness, the evaluation of the entropy parameter seems to be affected by the local conditions near the bed. In order to investigate such influence, the present work proposes an explicit relationship between the entropy parameter and the relative submergence. This relation was validated using data collected in a rectangular tilting flume of laboratory, where the bed roughness was composed by elements of regular shape such as spheres. Several tests were performed in conditions of large-scale roughness (1.9<D/d<6.4) and for different values of slope (0.05%<i<1%) and water discharge (7l/s<Q<76l/s). The method shows a good agreement between the observed and calculated data for both the velocity profiles and water discharges.