| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 102 === As the global warming, the heavy rainfall frequently caused the landslide and debris flow entering the river channel, and evolving into natural dam in Taiwan. The
over-topping of the landslide dam can induce the failure of the dam, the secondary damage of the river channel, and even involve the life and property safety of the residents living on the downstream area. This study select Landao creek in Huisun experimental forest of National Chung-Hsing University to conduct the first field testing of natural dam failure in the world. The field test adjusted the desilting gate to control the discharge and also combined the technique of photography and ordnance survey to analysis the failure course. By the reliable of the field test analysis, the system of natural dam failure experiment can be actual established.
The result of the field experiment shows that the velocity of the natural dam water level incensement is affected by the shape of water volume dam and the piping of the dam. It gets slow by the incensement of the water level. In the course of the dam failure, the changing velocity of the water level increases by broadening of the breach at the initial state and decreases till the stabilizing of the breach development.
When the water level of natural dam reaches the maximum value, the flow of the over-topping will pass through the dam and cause the retrogressive erosion. A large failure occurred since the top of the dam formed a main groove. From the result of two cases in single dam experiments, the breach reaches the maximum flow velocity and discharge value about 60 seconds after the over-topping of the natural dam. Then,the flow velocity and discharge value will slow and stabilize by the broadening of the breach and the decreasing of the water level.
The main interaction infection of the serial double-dam is the water flow from the upstream. The inflow from the upstream cause the water level of the dam increase and shorten the infection time of the water storage and the piping of the natural dam.
In this experiment, the distance of two dam bodies is 100 meters. If the distance of the two dam gets to large, the flooding time will increase,the infection of piping and
mostly the type of the downstream dam will transform from over-topping into piping failure.
This study proposes the infections of piping interacting with the dam: (1) Causing the internal emptied of the dam and inducing the dam sliding or collapsing while the crack happened on the top of the dam. (2) The washing failure of the downstream face of the dam. Besides causing the change of the failure type, it might change development of the breach if the dam is failed by over-topping. (3) The flow storage of the natural dam is infected by the piping during the dam failure.
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