On Flow Resistance Due to Vegetation in a Gravel-Bed River

摘要

Using hydraulic data collected in thirteencross-sections in a 250 m long reach of Babolroud River, Iran, this study investigated the relation between flow resistance and vegetation in a gravel-bed river with vegetated banks. It was found that the maximum flow velocity occurred on the water surface for bare bank cross-sections, but near the vegetated banks the dip phenomenon was observed and the maximum velocity occurred below the water surface for vegetated cross-sections. The log law is valid at various distances from vegetated banks in gravel bed rivers with different commencement levels. The flow resistance was found to be an exponential function of the average relative roughness with the coefficient of determination 0.733. Correlation of coefficient of 0.943 was obtained by charting between relative velocity and nonlinear equation dependent on relative roughness, Reynolds number and plant inclination factor. More field investigations are needed to quantify and localization this relation.