Determination of friction factor for rivers with non- submerged vegetation in banks and floodplains

Abstract

Due to vegetation flexibility, friction factor varies in flood plains and river banks and is a function of vegetation characteristics and flow conditions. Study of river behavior and effect of vegetation on river systems are very important for water intake in pumping stations, water treatment plans and wastewater and construction of structures such as bridges and diversion channels. Purpose of this research is to develop a relationship for estimation of non-submerged vegetation roughness in the flood plains and river banks. Number of 182 experiments was conducted on a laboratory flume and effect of parameters on the roughness coefficient was evaluated. Results show a nonlinear decrease of roughness coefficient with increasing of flow rate. Increase of velocity from 0.2 to 2 m/s make Manning’s coefficient reduces to about 30% of the first case. Decrease of roughness coefficient with decrease of submergence ratio and density was low compared to the velocity effect. Key words: Friction factors, vegetation, flexibility, non-submerged.