Longitudinal Velocity Distribution and Manning's 'n' Coefficient in Open Channel with Unsubmerged Vegetation

Abstract

The effects of unsubmerged vegetation on velocity distribution and Manning’s n were investigated experimentally in the laboratory. Water level was measured by water level measurement system and velocity was measured by 3D acoustic Doppler velocimeters (ADV). The findings reveal that longitudinal velocity all has a minimum value at the location of 5m (longitudinal position) and the discharge of 70L/s, the minimum longitudinal velocity is 47cm/s, 44cm/s, 37cm/s and 35cm/s for 1m, 2m, 3m and 4m vegetation section length respectively. Based on the experimental data, the Manning’s n for various flow conditions as well as for vegetation patterns was determined. The Manning’s n varies between 0.04 and 0.09 in this study, and it decreases as the Froude number increases, while increases as the water depth increases. The effect of the vegetation section length on the relationship between the Manning’s n and Froude number is not significant.