The Impact of Vegetation on the Bank Erosion (Case Study: The Haraz River)

Vegetation establishment is a suitable biological method of erosion control. Bank erosion is one form of water erosion and its adverse effects include an increase in turbidity, degradation of riverbank lands, difficulties caused by sediments depositing in the downstream. The rate of riverbank erosion can be decreased by application of biological methods in sensitive reaches identified. In this study, a 3250 m section of the Haraz River was studied to evaluate the effects of vegetation establishment on shear stress, water velocity and finally on the bank erosion. In this research, Geographical Information System (HEC-GeoRAS extension), HEC-RAS software, and topographic maps of riverbed at the scale of 1:500 were used to simulate hydraulic behaviour of the Haraz River. In order to evaluate the effect of vegetation cover on the bank erosion, roughness coefficient of Manning was determined with the Cowan method for two seasons (winter and summer) separately, due to changes in vegetation in the considered sections during different seasons of the year. The results showed that vegetation establishment on riverbanks caused changes in water velocity, water depth, power of shear stress and this all should finally be reflected in the rate of bank erosion.