ABSTRACT
Boulders are sometimes placed in rivers to provide diversity of flow and then to enhance ecological function for aquatic lives. In order to make clear the effects of such habitat structures, the change of flow regime and bed configuration by single relatively large structure were investigated. At first, the flow structure around a sphere and hemisphere put on the channel center and beside the side wall was measured by using electromagnetic velocimeter in emerged and submerged conditions to understand fundamental flow pattern initiating bed deformation. The effect of hemisphere on flow variation was larger for emerged cases than for submerged cases although emerged cases have lower discharge. The maximum scour depth was almost 0.61 of the sphere diameter irrespective of the placement and relative flow depth. The scoured volume became larger in the emerged cases than the submerged cases. Next, temporal process of bed deformation was observed for side-placement sphere case. The scour hole was developing temporally in the form of concentric circle and the sphere sank rapidly and also moved upstream. The flow structure around the sphere on the deformed bed configuration was measured by using PIV method. Three-dimensional flow structures on the flat bed with sphere and on the deformed bed were compared.
