FLOW STRUCTURES AND SEDIMENTATION CHARACTERISTICS AROUND COLONY-TYPE VEGETATION AT FLOOD EVENTS
Colony models, comprising seven equally spaced cylinders with staggered arrangement are mounted on a water flume bed. The characteristics of flow structures around the colony-type roughness model in uniform flow were investigated. For elucidating the effects of the vegetation density and emergent or submerged condition of the colony-type roughness according to the flood water depth, drag force is measured with changing both of the relative space L/d and the relative height h/H,where L is the space between neighbored cylinders, d is the cylinder diameter, h is the model height and H is the water depth and the drag coefficient (Cd) is calculated. The flow structure around the colony models and the drag coefficients values are changed depending on L/d and h/H. Two types of flow structures, a large-scale Kármán vortex street behind the colony models and a primitive Kármán vortex street behind the individual cylinders are generated. The Cd in emergent condition becomes larger than that in submerged condition. The Cd increases sharply when h/H is ranged from 0.8 to 1.0 and then approaches the Cd value in unsubmerged condition. In field observation, sedimentation around the two roughness type was investigated. When the vegetation density is large, like willow, i.e. Salix subfragilis or Eragrostis curvula (colony-type vegetation), the sedimentation is occurred behind the vegetatation region When vegetation denesity is small, it occurres inside the vegetation region, i.e., Robinia pseudo-acacia or Phragmites japonica. Similar flow structure are supposed to be occurred in water flume experiment and irr field. This study elucidated the effect of vegetation density on flow structure.
Colony type vegetation Drag coefficient Flow structure Relative height Density
Norio Tanaka Shiho Ito Junji Yagisawa
Graduate School of Science and Engineering, Saitama University, Japan
国际会议
第16届亚太地区国际水利学大会暨第3届水工水力学国际研讨会(16th IAHR-APD Congress and 3rd Symoposium of IAHR-ISHS)
南京
英文
981-986
2008-10-20（万方平台首次上网日期，不代表论文的发表时间）