貯水池の決壊に伴う洪水・土砂流出量の予測

Abstract

Floods due to collapse of reservoirs cause severe damages to properties and losses of humanlives. Thus, a number of studies have been carried out in past years to solve the dam-breakproblem. In recent years, computer programs for the dam-break analyses have been developedto assess the potential hazards of the dam collapse, but the water and sediment release from areservoir has yet to be elucidated.This paper presents a method to predict the water and sediment discharge caused by thecollapse of reservoirs with a given water depth (ho), length (L), and sedimentation depth (D)on the basis of a simple experiment and a mathematical model. An approximate analyticsolution on reservoir depth and outflow rate for the total and instanteneous dam collapse wasderived from the characteristic flow equations, and verified by the experiment in a rectangularhorizontal channel. Changes in the outflow rate due to the opening speed of gate correspondingto the gradual dam collapse were also discussed.Meanwhile, the experiment of the water and sediment release from a reservoir showed thatthe outflow rate during the intial stage increases rather than that of the above solution due to theupstream migration of flow control section in the reservoir. The mathematical model in this casewas also developed using the method of characteristics and a sediment transport formula. Thecaluculated results of water and sediment discharge were consistent with the observed ones.Furthermore, the analytic solution for the initial stage demonstrated that the increment of theoutflow rate and the sediment concentration primarily depend on D/ho, and that the total volumeof sediment discharge is proportional to Lh0D.