Experimental Study of Floodplain Vegetation on Flow resistance

Rivers are the main parts of hydrologic cycle which are consist of special element and ecosystem. Flood plain vegetation classify in three types involving grass, shrubs and rees. These vegetation covers almost grow normally or by executing the bioengineering works. The vegetation covers impact on flow momentum reduction and energy dissipation by increasing the roughness and inundation which can cause many damages in flood plain. Roughness is one of the basic parameters in the hydrodynamic simulation models. An actual estimation of this parameter is necessary for calculating the flow parameters and also prediction of flood and sediment transport. This coefficient varies with the hydraulic condition and vegetation cover of the stream. A new method for estimation of Darcy and Manning coefficients are proposed as the result of this research. Different types of vegetation covers tested in this study in a physical model. The model consists of a trapezoidal compound channel which is installed in a flume with a length and width of 14m and 1.5m respectively. The longitudinal slope of the flume is considered 0.001 constantly. This flume installed in the Hydraulic laboratory of Soil Conservation and Watershed Management Research Institute( SCWMRI). In this research, the impacts of different vegetation covers on the flow resistance studied in the floodplain and main channel of a symmetric trapezoidal channel which is physically simulated in the flume. All the experiment conducted in the 5 level of water depth in the channel. Three types of vegetation covers investigated including trees (with the height of 22cm, non-submerged), shrubs (with the height of 8cm, submerged) and the composition of shrubs and trees. The arrangement of the covers for each type defines in 5 different conditions and three level of coverage density (30, 50 and 100 percent). Finally, by defining different scenarios for water depth, arrangement of vegetation covers and also its density, 225 experiments conducted with vegetation covers. Instead, 5 tests were done with no cover in the channel bed. A test section defines in the middle part of the flume for measuring the flow parameters. In each scenario, the water level and flow velocity measured in the test section, then Darcy and Manning Coefficients calculated with the correspondent results. After the analyzing the results of whole experiments, some relations proposed for estimation of these two coefficients as a function of coverage density and its submergence percentage and also the flow frude number.