| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 100 === Many people recognize the fact that forests play an important role in water and soil conservation and often attribute debris hazards towards poor watershed management. Through examining land use, topography, geology, and other environmental factors, this research uses Typhoon Morakot that happened in 2009 as an example to investigate the causes of woodland collapses. The research shows that the collapse rate of natural forests is 70.98%, which is higher than that of artificial forests which stands at 36.80%. The collapse rate of non-compartment land is 54.96%, which is slightly higher than compartment’s 52.78% collapse rate. Yet, the collapse rate of topographical, geological factors did not differ significantly.
However, the movement of the landslides can be divided into the occurrence section, the transportation section, and the accumulation section. When heavy rain occurs and destroys the disaster areas, a chain relation of compound disaster will happen. Therefore, if we only focus on interpreting the data of collapse areas, we will fall into the misconceptions. This will then lead to the misinterpretation of the data and the actual mechanism of collapse will not be reflected. During this disaster, the disaster areas are mainly located at road slope lands. The turning points of roads are prone to collapses during heavy rains due to overflow, therefore the key to collapse areas is overflow erosion of surface runoff at the turning points of roads during torrential rains. Researchers who investigate these disaster areas have to always be careful.
As the saying goes things will develop in the opposite direction when they become extreme. Geology becomes fragile at dense woodlands, and if forest degradation happens, it is very likely for it to become the source of driftwoods. Even though banning people from entering the forests can prevent human disturbance, once the sediment yields insufficiency in the channel of headwater will cause headward erosion. Moreover, although natural forests have the ability to perform water and soil conservation, the pressure of earthquakes and heavy rain will cause the phenomenon of “deposit small withdraw large”. The life span of a forest is limited, and collapses and landslides are part of a normal cycle of energy release. A modest renewal of old trees, the concepts of equilibrium of sediment transport, and the calibration of potential collapse areas is the focus of management strategies for forest lands. People should be vigilant and learn to get along with nature.
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