堤防決壊による土砂堆積のシミュレーション

Abstract

A numerical simulation method is presented for analysing the area and thicknessof deposition due to both of the suspended and bed-load sediments in a protectedlow-land when a river bank levee is broken. This model is constituted by themomentum equations of fluid, continuity equations of fluid and sediments, bed-loadand suspended load equations and so forth wth respect to the horizontally two-dimensional overland flood flows.The laboratory experiments on bed-load deposition in the protected low-landdue to river bank breach are done, where the experiments are accomplished byusing two different types of experimental set-ups, I. E., one has a straight steel flumehaving a bank breach point at one side wall of the flume, from which released flowoverflows on a square flood plain, the other has a wooden flume set up at a rightangle to one side of the flood plain to model a breach point. Both of the calculatedand experimentally observed bed-load sediment depositing areas and thicknessesinside the areas are in comparatively good agreement in every cases. Moreover, laboratory experiments on the deposition of suspended sediment in the protected low-land are also carried out, where the meandering stream channel is constructed inthe square flood plain area enclosed by the banks. The experimental circulardepositing area and the thickness distribution inside the area are compared with thecalculated ones. The experimental results are well explained by the calculation.This simulation method is applied to the actual flood plain (Ogura basin, situated in the south of Kyoto Prefecture). It is found that preparation of a hazardzone mapping in respect to the sediment deposition due to river bank breach ispossible by calculating the bed level variation in the flood plain with this simulationmethod under several imaginary bank breach points and bank breach processes.