A study on Control of Open Channel Flow by Vegetation for Wetland Conservation

Behavior of the fine sediment around vegetation is still unknown because knowledge of complex flow around vegetation is limited. Moreover, only limited research has been done on flow resistance and fine sediment transport inof open channel flow wherewith vegetation that considers a growth type, which includinge emergent plants, submerged plants, and land plants, etc., has been considered are hardly researched. This study considered the growth type of vegetation and analyzed the flow of water with vegetation that considers a growth type of vegetation by using laboratory experiments that includeds various methods such as LDV and numerical simulations employing turbulence model. For emergent plants, it was found that the lateral momentum of transport reachedtakes a peak value at a certain vegetation density which wasis much larger than the density of the actual reed field, and the cause of this wascause related greatly to the shape of the horizontal vortex. WhenFor the case in which the ratio of a vegetation group's length to width wasis nearly 1:.7, the horizontal eddies were generated at the boundary of the vegetation group's region, and the momentum of transport reachedtakes a peak value. A numerical computation employing SDS&2DH turbulence models was introduced to investigate the resistance and the roles of the surface and submerged vegetation layers, and the effect of generated turbulence. Theseis models allowed us tocan predict the mean velocity of the surface and submerged vegetation layers, and provided information on the shapes of vortices, lateral distributions of the depth averaged flow velocity, and turbulence statistics. A phenomenon involving wavy motion of very flexible submerged vegetation (termed honami) was observed, and the displacement of the plants was found to be closely associated with the structure of the turbulent flow, which yieldeds a larger Reynolds stress near the top of the vegetation layer. Finally these experiments and simulations applyied to the development of methods for catching fine sediment method for the wetland conservation.