An open channel with an emergent vegetation patch: Predicting the longitudinal profiles of velocities based on exponential decay

Abstract

In an open channel, a vegetation patch increases local flow resistances, which impacts velocity fields inside and outside the patch. A series of experiments was performed to investigate the longitudinal evolution of velocities in a channel with an emergent vegetation patch. Near the upstream edge of a patch, lateral flow adjustments led to decreased velocity inside the patch and increased velocity in the adjacent bare channel. A model based on exponential decay was proposed to predict the longitudinal profiles of streamwise velocities upstream of and inside a patch and in the bare channel. The longitudinal transect across a patch was divided into two regions. In each region, the e-fold decay parameter was determined. Fourteen groups of velocity data from cases of model and natural rice patches were used to verify the proposed model. The predicted velocity profiles agreed well with the measurements in both the vegetated region and the bare channel, indicating that the proposed model is capable of predicting the longitudinal profiles of velocities inside and outside a patch.