Experimental Investigation on the Effect of River Bank Tree Planting Array, on Shear Velocity

In this paper the effect of tree planting in a river bank on the shear velocity of flow was studied in a laboratory environment. At first a physical model was established in a 1.5m wide, 30m long experimental flume with a longitudinal slope of 0.01. Then a number of bars with 6.5mm in diameter, stimulated as trees, were located on the bank surface with a slope of 1:3 in two different orientations (square and triangular forms), three different heights (5, 6.5 and 8cm), and three different intensities (6*6/6*3, 8*8/8*4, 10*10/10*5). After that, the flow hydraulic parameters (such as discharge, water level and velocity) and their variation versus the change in experimentally planted trees were measured and analyzed. At least 19 series of laboratory tests with 5 different discharges were implemented. The results showed that, there is a relationship between planted tree and shear velocity. Also relationship between shear Reynolds (Re*) and the average velocity to shear velocity ratio (U /U*) showed that vegetation could increase the roughness coefficient also by increasing the tree density, the ratio of U /U* and the roughness are increased. The roughness coefficient in all cases of not using vegetation, tree planted in square form and tree planted in triangular form, was increased respectively.