The roughness coefficient is function of physical characteristics of flow, such as water depth, velocity, type and density of vegetation coverage. Impact assessment of vegetation coverage on flow roughness coefficient and trapping of sediment in experimental condition were the research aims. The research tests were conducted in different water discharge, various slope of substrate and three density of coverage using physical model. Relations for estimation of the Manning's coefficient were developed using statistical analysis. The best performance of model in estimation of the flow roughness was gained at 12% density of coverage and steady injection of sediments.