台灣受到地形陡峭、地質破碎、颱風豪雨事件頻繁之影響,加上山坡地過量開發,因此經常發生區域土砂災害,造成上游土砂災害事件增加,近年來極端降雨事件造成環境劇烈變化,土砂災害發生的頻率與規模也隨之增加。有鑒於此,近年有多位專家學者致力於土石流之相關研究,以期更了解土石流發生機制、流動過程與災害狀況,期減少土石流災害所造成的衝擊及損失。 因此本研究以南化水庫上游河道後堀溪為研究對象,為瞭解河道之變異情況,首先利用HEC-RAS模式,配合不同重現期距(25年、50年、100年及200年)之洪水量,模擬河道洪水水位及河床沖淤之變化,並與現地調查結果進行驗證。模擬結果顯示,不同重現期距之洪水流量並不會對橋梁橋板及河岸階地有所影響,但加入土砂因子後,發現河道之沖淤分布狀態差異不大,但整體而言沖刷長度以重現期距25年及50年最多,而淤積長度則以重現期距100年及200年為最多。 此外本研究為探討在極端條件下,對後堀溪之影響情況,因此模擬不同土石流濃度對後堀溪河道之影響,利用FLO-2D數值模式,配合雨量資料、數值地形模型及土砂資料,模擬不同土石流濃度(Cv=27%、35%、45%及55%)對河道的影響,結果發現當土石流濃度達到45%時,木瓜坑橋鄰近河段及保全對象將受到土石流之影響。
Sediment hazards often occur in Taiwan because of steep terrain, active fault, concentrated rainfall, and hillside over exploitation. And extreme rainfall in recent years caused surroundings change intensely, increasing frequency and scale of the sediment hazards. The Houjue River which is primary watercourse of the reservoir Nan-Hua is research area. In order to understand the change of this channel. HEC-RAS model which combined with the return period 25-year, 50-year, 100-year, and 200-year was used to simulate the mobile changes of river sedimentation volume. The accuracy of the numerical simulate result will be verified by the field survey result. According to the simulation, the flood won’t affect the riparian terraces. When we increased sediment factor to simulation, we find the 50-year return period is the maximum in the scour section of the channel, the second largest is the 25-year return period; the 100-year and 200-year return period are the maximum in the deposit section. To investigate the influence of the Houjue River in different sediment concentration. FLO-2D software (two-dimensional model to simulate debris flow and flood) which Combined with rainfall data, DTM, and sediment data was used to simulate different sediment concentration (cv=27, 35, 45, and55%) of the debris flow affect the primary watercourse of the Houjue River. we find when cv is over 50%, the change of deposition depth, flow velocities, and volume deposited is more obvious.
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