Author(s): Norio Tanaka; A. Shin-Doboku Kenkyusho; Tetsuya Kaneko
Linked Author(s): Norio Tanaka
Keywords: No Keywords
Abstract: In the downstream of a weir,the sediment discharge decreases and several bedtopography changes take place as for example the formation of sand bar in river mouthor the bankside erosion.Because a hemispheric obstacle on a flat plate producescoherent eddies with upward flow(Tamai,Asaeda and Tanaka(1987)),if the obstacleis placed in front of the weir where sediments are accumulated,it will be able tosuspend the sediment particles and to transport them downstream of the weir(seeFigures 1(a),(b)).As the upward flow generated behind the obstacle changes thedistributions of velocity and suspended load,it can be expected to increase the amountof the sediment which pass over the obstacle.The change of the bed topographyrepresents the amount of suspended sediment in an unsteady process.On the otherhand,distributions of velocity or suspended load after the scour hole becomes stablerepresents that in a steady process.Therefore,the ability of the obstacle as a sedimentsuspension promotor can be discussed by the change of bed topography,distributionsof velocity and suspended load.Althogh roughness is widely accepted as resistancein fluid mechanics,there must be pointed out that in the present case from the pointof view of resistance the obstacle plays a secondary role in comparison with the weir.Therefore,as far as resistance is considered,the obstacle can be neglected.This is afirst step to the control of sediment transport by coherent eddies.Obstacles will beutilized as a sediment suspension promotor in the near future.
Year: 1991