Physical and Numerical Modeling of Submerged Vegetation Roughness in Rivers and Flood Plains

Abstract

The Manning’s n-value, a fundamental resistance coefficient to balance driving forces of a river stream, is known to depend on the flow condition (depth and velocity) as well as vegetation condition (type and density). In this study, flume experiments were conducted to investigate the variation of n-value with flow and vegetation conditions for submerged vegetation in river beds, banks, and flood plains. Artificial plastic plants, for a length of 8 cm, were laid on the floor of a 4-m-long section of a variable slope flume. The Manning’s n-values were estimated for different slopes, discharges, flow depths, and vegetation densities. The results reveal that the Manning roughness coefficient (n) increases as vegetation density increases, whereas it decreases when the flow depth and velocity increase. The proposed physical model in this study was customized as a subroutine in a numerical model (FASTER) for a large river reach. The estimated water levels and discharges by the model were much closer to the fiel...