Author(s): M. Fathi-Moghadam; N. G. Ebrahimi; S. M. Kashefipour
Linked Author(s): Manoochehr Fathi-Moghadam, Seyed Mahmood Kashefipour
Keywords: Submerged Vegetation; River; Flexibility; Manning's coefficient
Abstract: An appropriate estimation of a river roughness coefficient (n) requires understanding of the flow condition (depth and velocity) as well as vegetation condition (type and density). In this paper, flume studies were carried out to investigate the hydraulic effects of bed river grass coverage on the flow shear velocity. The study is based on the results of the 60 experiments which were done using the laboratory model with the different longitudinal slopes (from 2:1000 to 1:100). The flow discharges varying from 10 to 40 liters a second and three vegetation densities were examined. All experimental data were collected using the newly constructed facilities in the Hydraulics Laboratory at the Soil Conservation & Watershed Management Research Institute, Tehran-IRAN. The results reveal that the Manning roughness coefficient (n) increases as vegetation density increases, while it decreases when the flow depth and velocity increase. A relationship between Reynolds shear parameter (Re*) and the ratio of average velocity to the shear velocity (U/U*) also confirmed the increase of Manning's n-value with vegetation density.
Year: 2009