Numerical simulation of the Debris Flow Occurred at Izumi City on July 10, 1997.

点击翻译按钮获取中文摘要

Debris flow occurred at Izumi city , Kagoshima Prefecture on July 10, 1997, and so 21 people died because of this event. The debris flow was caused by the failure of mountain slope of the angle of 26°. After the slope failure the debris moved down slope of 6.8° and deposited on the alluvial fan of lope angle of 3.7° 〜2.4°. It is important to make debris-flow hazard map of this area as its counter measures. The purpose of this study is to accumulate the knowledge for numerical simulation method of the debris flow.The results obtained in this study are as follows :(1) In order to examine the process of debris-flow termination, experiments of debris flow were made in an open channel with rapid decrease in slope from 4° or 6° to 2°. Bed materials used in the experiments are fine sand with the diameter of 0.17 mm and coarse sand of 0.84 mm. In the case of the coarse sand considerable deposition occurs at the changing point of channel slope. At the same time deposition area extends to the downstream and upstream directions. In the case of the fine sand considerable deposition occurs in the more downstream area from the changing point of channel slope. At the same time deposition area extends to the downstream direction.(2) Numerical simulation of these experiments was made ; the basic equations are the momentum equation and two continuity equations for solid and fluid phases. Sediment transport equation is necessary to solve the basic equations. Two different types of sediment transport equations are used ; one is a bed-load transport equation and the other a total-load transport equation. The result of computation with the bed-load transport equation agrees with the experiments in the case of coarse sand. However the result of computation with the total-load transport equation cannot explain the experimental results in the either case of coarse sand or fine sand.