抄録
Sediment flushing operation from large dam causes bed condition change in the downstream. It may reduce the flow resistance as the flushed sediment fills the voids among the large stones. This condition influences the flow in roughness layer which is important habitat not only for benthos, but also for swimming fishes. However, the hydraulic condition changes in roughness layer due to sediment supply is not well investigated. Furthermore, its impact to habitat is not considered neither. In this study, we investigated the hydraulic characteristics changes within the roughness layer due to bed topography changes as one of the impacts from sediment supply in natural rivers. It was conducted over immobile bed condition in experimental flume. Detail velocity measurement results within the roughness layer and the turbulence properties are presented. Besides that, suitable method to evaluate the roughness height as the bed condition changing is also discussed. The results exhibited the reducing of spatial variance of spatially averaged mean velocity, TKE, and Reynolds shear stress within the roughness layer associated with decreasing of bed roughness as the sediment fills the voids among cobbles. We also observed the decreasing of roughness layer thickness as the bed roughness reduced. This experiment helps to explain that sediment supply is not only reducing flow resistance but also limits habitat preference of benthos and swimming fishes as velocity distribution becomes homogenous within the roughness layer.
