Author(s): I. Fujita; Y. Muto; Y. Shimazu; R. Tsubaki; S. Aya
Linked Author(s): Ichiro FUJITA
Keywords: Field observation; Velocity measurements; Large-scale particle image velocimetry (LSPIV); Spur dyke; Flooding; Channel conveyance capacity; Boil
Abstract: Field observations on the surface flow were carried out in a straight reach of the Uji River, Kyoto, Japan. Velocity distributions on the water surface were obtained based on the captured video images by means of large-scale particle image velocimetry (LSPIV). Flow structures around spur dykes are studied for both non-submerged and submerged cases. It is clearly seen that, for both cases, the dykes are working as an additional roughness. Their effect on channel conveyance capacity is estimated in terms of the effective channel width calculated from the velocity distributions. For the non-submerged case the area enclosed by the spur dykes has little contribution to the channel conveyance capacity. Whereas for the submerged case the streamwise velocity is fairly decelerated on the dykes' side due to the drag effect of the dykes themselves. It is also of interest that the maximum velocity filament appears at a different position as the water depth varies in case of the channel with single-side dykes such as studied here. In addition, large-scale boils shedding from the submerged dykes are clearly observed and their origin and advection mechanisms are also evaluated from the video image. Time period of boils appearing on the water surface is well related with the time calculated by the mean upward velocity and the water depth on the dyke.
Year: 2003