Manning Roughness Coefficient for Rivers and Flood Plains with Non-Submerged Vegetation

Manning’ n-value varies in vegetation zones of river and flood plains due to variation of vegetation flexibility and flow depth. 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, fish pools in the river banks and construction of structures such as bridges and diversion channels. Purpose of this research is to develop relationships 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 m/s to 2 m/s make Manning’s coefficient reduces to one third of the first case. Decrease of roughness coefficient with decrease of submergence ratio and density was low compared to velocity effect.