CONTROL OF FLOW AND BED EVOLUTION IN CURVED OPEN CHANNELS WITH STICK ROUGHNESS

摘要

Permeable structures like pile dikes or vegetation are located on curved reaches of rivers to protect levees from scouring, but their effects on 3-D flow structures including pressure-driven secondary flows and bed evolution are still not clear. In this study, three-dimensional mean flow structures were measured in a curved open channel with different height of sticks arranged along the outer bank. The secondary flow cell was generated in the same manner as the smooth rectangular cases, but the outer-bank vortex diminished as the stick height becomes larger. In the case of submerged stick roughness, the secondary flow cells were driven by the effect of roughness heterogeneity in a cross section. As the results, the secondary flow cells were formed throughout a cross section and were more enhanced than the no-roughness case and the non-submerged roughness case. The bed shear stress was evaluated by close measurements of near-bed velocity and the effects of the stick roughness on bed evolution were investigated. The stick roughness located along the outer bank reduced scour but the final bed forms were different in response to the height of the stick roughness.