床固め直下流部の局所洗掘過程のモデル化

Abstract

A consolidation work, which may be called a submerged sill, is constructed across a river channelin order to prevent the river bed from being lowered due to a dam construction. The stability of itsfoundation should not be threatened by the local scour downstream of the sill. In this study, char-acteristics of the scouring process downstream of a consolidation work are discussed experimentallyand analytically, using a simplified flow model. The flow downstream of a submerged sill has towpatterns; submerged jet and undular jump. In the state of submerged jet, the main flow is deflecteddownwards and sweeps along the bed with a roller near the water surface. On the other hand, in thestate of undular jump, the main flow is shifted to the water surface and a roller is formed near thescour hole bed. These two flow patterns appear alternately in the scouring process. Modifyingthese two flow patterns under some assumptions based on the experimental facts, the distribution ofthe bed shear stress in the scour hole is estimated and the variation of the scour depth with time andplace is simulated by solving numerically the equation of continuity of the bed sand under the non-equilibrium state of sand discharge.