Velocity measurements around non-submerged and submerged spur dykes by means of Large-Scale image velocimetry

Fujita Ichiro

Muto Yasunori

Shimazu Yoshiro

Tsubaki Ryota

Aya Shiro

Journal of hydroscience and hydraulic engineering

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 the Large-Scale Particle Image Velocimetry (LSPIV) developed by Fujita et al. (3). Flow structures around spur dykes are studied for both non-submerged and submerged cases.

It is clearly seen that, for both cases, the dykes work 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. Their origin and advection mechanisms are also evaluated from the video image. The 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.

建設工学・土木工学 [ 510 ]

英語

土木学会水理委員会

(c) 2004 公益社団法人 土木学会. All rights reserved.

[ISSN] 0912-2508

[NCID] AA1045915X

[URI] http://www.jsce.or.jp/publication/e/book/book_jhhe.html#221