Various investigated methods of aerial photographs, geomor-phological characteristics, geological condition, geomaterial properties and stability analysis were used to identify these hazardous mechanism by two debris flow cases in Tungmen, Hualien and Shing-Yi, Nantou. The investigation results demonstrated that these deposited materials were triggered and moved downward to the lower part of the gully by high intensity precipitation. These geomaterials coverged from the sidewall of the gully by cutting and erosion from the moving debris flow.
Understanding the mechanism of debris flow occurrence will be helpful to clarify the factors inducing debris flows, and to propose counter measures. This paper introduces the characteristics and developing process of debris flows, as well as the favorable conditions for debris flow mobilization. Besides, four types of debris flows and their mechanisms are described in detail. The research in this area is also introduced.
The objective of this paper is to explore the effects of different modes of water supply on the occurrence of debris flow. The physical model was used with water supplied from the upstream tank to simulate surface runoff, and with water supplied from hoses in the base to simulate the upwelling of ground water. It is found that the debris flow caused by surface runoff has a smaller scale and behaves more like erosion process. The debris flow caused by upwelling of ground water has massive movement and is induced by lowering of effective stress. The characteristics of the two different modes can be used to verify the field conditions with enough field evidences.
In this study, Feng-Chiou was selected as a site to investigate the methods for establishing the critical rainfall line of debris flow occurrence of first order streams. The methods presented in this study consisted of the proposed method and the conventional methods. These methods were also compared in this study.
The critical rainfall line of the debris flow occurrence is the foundation of the warning system of debris flow. In the conventional method, the critical rainfall line is determined by using the relationship between effective rainfall intensity and effective cumulative rainfall amount, which is applied on large area basins. In the proposed method, the critical rainfall line is determined by using the relationship between effective cumulative rainfall amount and duration, which can be applied on first order streams. In the proposed method, recession coefficient is considered. Using the proposed method, Feng-Chiou was selected as a site and the critical rainfall line of debris flow occurrence of the site was then established. The new method is expected to be a better basis for the warning system of the debris flow of first order streams.
The development of slope land in Taiwan is rapidly growing, so is the potential hazard for debris flow. Therefore, identification of these potential hazard area will be an important task. The flowbility of debris flow is a control factor in estimation these area. This paper develops a numerical model utilizing nonlinear constitutive relationship and fluid conservation laws. Model can be used in field and the values of all parameters used in the model can be obtained through simple in situ tests. Results from numerical modeling fits those from flume tests very well.
This paper introduces the formation of debris flow fan according to the mechanism of deposition from debris flow . And the developing process of debris flow fan, which is influenced by geomorphological factors , damaging scales and depositing conditions , is discussed in order to grasp the dangerous zone. Meanwhile, the technical principles for the delimitation of dangerous zone as the designation area of soil and water conservation also are mentioned for management and protection to minimize or avoid the risk of debris flow.
The destruction of debris flow comes from its containing a lot of granular soilds and also its quick movement. Fluid pressure and impact of large boulders are two factors contributing to the impact force in its quick movement. The countermeasure structures of debris flow are built to reduce the amount of debris and slow down the velocity of its movement. On the upper section of the stream, the structures are to reduce the amount of debris and avoid transformation of debris flow. On the middle stream, the structures are to retain and slow down the debris flow. On the lower part of the stream, the structures serve as a way of eliminating damages from accumulation. In Taiwan, the closed-type of sabo dams are mainly used as the retaining method of countermeasures. However, the open-type of the permeable dams have been gradually increasingly adopted in recent years.
Harbor facilities are generally constructed of concrete, steel, earth, and rock materials. All of these materials deteriorate or may experience movement due to specific loading condition over time. Periodical inspection of these structures is required.
An old wharf was investigated and studied. The purpose of this paper is trying to establish a general rule or procedure for the investigation and evaluation of the safety of harbor structures.