An experimental study of flow through rigid vegetation

Better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation. Instead of spatial averaging, this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels. Velocity data was collected with a one dimensional laser Doppler velocimeter under emergent and submerged flow conditions. The effects of dowel arrangement, density, and roughness were also examined. The results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it, however the boundaries are marked by inflection points. The strongest vortices and turbulence intensities can be found there, especially in the region immediately downstream of a dowel. These results support the idea that the flow in the region near the bed and at the top of the dowel array is very unstable leading to the formation of coherent structures and are areas of significant mass and momentum exchange.