| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 104 === Since revetment is the front line of defense against flood, the development of a reliable revetment failure early-warning framework is very important especially for metropolitan area. The purpose of this study is to develop a revetment failure early-warning framework considering the forecasting uncertainty. The Tesheng River is chosen as study site and the development of early-warning framework includes the following steps:
(1) Analyze the mechanism and cause of revetment failure. In general, the major failure mechanism includes the hydraulic force resulted from shear stress and the geo-instability due to toe erosion.
(2) Generate many realizations of Manning’s n and inflow hydrograph by Latin Hypercube Sampling technique (LHS). Shear stress and water level under different combinations of Manning’s n and hydrograph were simulated. The simulation results were then used to determine whether the revetment will fail or not. Two failure modes are considered in this study including the surface erosion due to excess shear stress and the overturning of revetment due to toe erosion.
(3) The analysis results from the previous step show that the water level could be a major index to judge that the revetment will fail or not in the following hours. Therefore, a framework was proposed which enables the pre-determination of thresholds of water level for revetment failure early warning under various combinations of toe erosion, pore pressure behind the revetment, and stipulated probability of type II error (i.e., failure to warn).
(4) Analyze the statistical properties of water levels at one and two hours prior to failure from which the warning water levels were determined.
The verification results showed that the actual and stipulated probabilities of type II error are close for the concrete type revetment. However, the actual probability of type II error could be much less than the stipulated value for gabion.
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