2015 Volume 21 Pages 137-142
The large local scouring of which maximum depth is up to 20 meters occurs in the Kiso river, and it is still expanding. In the scouring area, complicated flow condition, such as reverse flow, is observed, and it is supposed that it has possibility to drive expansion of the scouring. In this study, vortex structures and causes of expansion of the scouring are estimated by ADCP survey and three-dimensional numerical simulation. As the result, large vortex structures, such as horizontal and vertical vortex, were confirmed. And it is estimated that the vortex contribute little to the upstream expansion of the scouring area. On the other hand, it is confirmed that strong descending current on the upstream edge of the scouring occurs at small-to-medium flood. Then it is estimated that the current drive the increase of shear stress there and upstream expansion of the scouring area.
