河川堤防の決壊に伴う外水と土砂の流入について

Abstract

Breaches in river levees are accompanied with inflow of river water and sediment whichdetermine the flood damage. The inflow rates and volume are controlled by the hydraulicproperties of the breaches. Two kind of experiments have been carried out in order to find outmajor factors governing the inflow of water and sediment through the breach. One of them is alarge-sized experiment accounting for the river flow and the other is measurement of velocityfield around breaches fixed with epoxy resin. The inflow rates of the river water can beestimated from the relation of the control section but active flow width need to be evaluatedin cases of larges levees and widened breaches. Scour holes in the breaches migrate downstream, filling up the upstream part of them and deposit sediment is supplied from levee body andriver ground of upstream side of the breaches. Turbulence of the inflow is more intensein cases with fine material of levee and ground than those with coarse one because of largechange in longitudinal profiles. The inflow increases in the Froudean number from 0.2 or0.3 to almost 2, passing through the breach. It implies the existence of the control sectiom, which appeared near a location with the narrowest width of the breach. Two FEM analyseswere tried to predict the two dimensional flow field, by using a personal computer. One ofthem yield a fairly good estimation for the experimental measurement.