2012蘇拉颱風花蓮災害特性探討

2012年8月2日蘇拉颱風重創花蓮北段，災害集中於蘇花公路沿線，可分為三類：其一是蘇花公路沿線陡峭邊坡之崩塌；其二是山麓線下與河溪沖積之扇緣低窪區的水災；其三是谷口區的土石洪流。短時間、近千mm之強降雨量固然為誘因，但部分災情發生在研究者所劃定潛在危險區之外，其致災因素亟需進一步釐清，以為後事之師。本研究以地形、地質因子，輔以現場調查，分析致災之原因與特性。結果顯示蘇花公路沿線上、下坡皆為陡峭岩壁，時有崩落之虞；河谷材料多粗粒，急流將土石往下推動，堆積在能量轉弱處，阻擋後達的土石，形成土堤，導致豪雨中急速抵達的大量土石與洪水受到土堤的阻擋，轉而往緊臨社區宣洩。此類災害與依重力作用往下、整體移動的土石流不同。聚落應與溪流維持適當的緩衝區，並保持溪流暢通，以降低溢流衝擊的機會；適度增強房屋結構與擡升其高度，以減輕洪水危害。最重要的是，提昇一般民眾與災區居民防救災風險意識，才能及早查覺災害發生徵兆，及時進行有效因應。

關鍵字

蘇拉颱風；災害；崩塌；土石洪流

並列摘要

On August 2 2012, Typhoon Saola hit the northern part of Hualian and induced heavy damage to the County, especially along the Suhwa Highway. The disasters can be categorized into three types: First, landslides on the steep slopes along the Suhwa Highway; second, flooding in the lower foothill regions and along the frontal rims of alluvial fan; and third, debris floods at the valley entrance. Besides these disaster-prone areas, some of the areas which were previously thought to be potentially low in risk were devastated as well. While extreme rainfall which reached 1000 mm in a short period of time could be a significant contributing factor to the disasters, further investigation is warranted to clarify the causes and to provide crucial references for future prevention. The geomorphological and geological factors of the disaster areas were first analyzed and field surveys were conducted. The result shows that the frequent landslides on the steep slopes along the Suhwa Highway produced a great quantity of coarse debris. These materials are brought down along the channels by torrential storm flows, and are often deposited in areas where the flow energy dissipated because of the configurations or gradients of the channels. The initial sedimentation blocks the advancement of the debris which comes later, and gradually develops into more prominent obstacles. When the extreme high flow of the debris-laden stream rushed down along the channel and was blocked by the high obstacle, it was detoured to the side and topped over the slightly lower bank to inundate the nearby community. The mechanism of this type of debris floods is different from the gravity driven debris flows. In order to reduce the susceptibility of the communities to this type of hazards, proper buffer zone between the communities and the stream channels should be preserved, and the channels should be dragged constantly to maintain their conveying capacity. The structure and height of the houses along the valley sides should be enhanced to reduce possible flood damage. Most of all, the residents’ hazard awareness should be cultivated so that earlier alerts and consequent alleviation measures could be made possible.

並列關鍵字

Typhoon Saola ； disaster ； landslide ； debris flood

國際替代計量

2012蘇拉颱風花蓮災害特性探討

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