Longitudinal Dispersion Subjected to Rigid Vegetation in a Channel

摘要

Estimation of longitudinal dispersion coefficient is an important parameter for dispersion of the contaminants and hence can be used in any river water quality management intervention. Since the natural river water body is dominated by the presence of vegetation, it is expected that the longitudinal dispersion coefficient will be affected by the presence or absence of the vegetation. Hence in this study the effect of vegetation on longitudinal dispersion coefficient has been studied. Experiments have been conducted in a channel having rigid vegetation using rhodamine as tracer and concentrations of rhodamine is measured at various time intervals at 2 and 4 m downstream from the point of injection. The longitudinal dispersion coefficient is determined in the presence as well as absence of vegetation in the channel having Reynolds number varying from 2500-10000 and Froude's number varying from 0.02-0.05. It is found that the longitudinal dispersion coefficient downstream to the vegetation is affected in the presence of the vegetation. It is also found that the dispersion coefficient depends on number of rows of vegetation but significantly depends on the diameter of vegetation. A new functional relationship between dimensionless terms is derived using dimensional analysis for predicting the dispersion coefficient.