Flow Resistance in Open Channel with Emergent Rigid Vegetation

Abstract

This paper presents the flow resistance in open channel flow with emergent rigid vegetation. Vegetation can be actively used as flood management resistance tool, enhance the sustainability and restoration of the ecosystem. Irregular growth of vegetation in channels increases the hydraulic resistance which leads to energy loss and conveyance capacity which can be problematic. The flow resistance produced by uniformly distributed vegetation stems has been thoroughly investigated from the previous experimentations. The vegetation consists of rigid rods replicating stem of a tree. Velocities were measured using 3-D Acoustic Doppler Velocimeters (ADV), with both downward facing and upward facing probes. It has been observed that behind the vegetation stem, the magnitude of the longitudinal velocities became very less. However, the other two velocities i.e., transverse and vertical velocity were high due to occurrence of turbulence. The results show that flow resistance varies with flow depth, vegetation length, stem diameter and vegetation density. Also it has been observed that the flow rate decreased with increase in vegetation density. Experimental data sets of NITR and past researchers have been taken for developing a new mathematical relationship for roughness in terms of non dimensional parameters. The mathematical expression has been proved to match well with the experimental data sets and found to be better as compared to that of the conventional equations.