土石流災害影響範圍模擬與治理工程評估-以屏縣DF071為例

台灣位於板塊交會處以及西太平洋颱風路徑上，好發地震與颱風，近年來在極端降雨事件頻繁侵擾全球的情況下，台灣又因地形限制，朝向山坡地開發，在高強度降雨情況下，使坡地因開發或本就破碎的岩層更容易發生崩塌，加上豐沛的水源供給，土石流事件發生的更加頻繁。有鑑於此，防減災工作應為第一優先，以減少災害造成的衝擊及損失。本研究調查了研究區域的堆積環境和易受災區的位置，調查結果顯示，集水區中上游多處崩塌，部分河段有明顯的土砂淤積情形。這些土砂有可能對下游的保全住戶以及台26線造成安全隱患。本研究採用京都大學開發之二維土石流模式 (Hyper KANAKO)模擬屏縣DF071土石流災情的流動情況。結果顯示，在降雨重現期距50年時，屏縣DF071將會發生溢流，對下游保全住戶以及台26線造成影響。本研究建議透過架設穿越台26線的涵管的方式進行分流以及將河岸高程不足處進行增高。結果顯示，工程改善後以不會發生溢流。此外，亦在不同降雨重現期距之洪峰流量下 (10年、25年、50年、100年及200年)，設定不同土石流粒徑進行流況分析，探討屏縣DF071下游之土砂堆積情形。模擬結果顯示，隨著粒徑增大影響範圍有增加的趨勢，但變化量不顯著，尤其重現期距小於25年時，影響範圍的變化量甚微。土方量隨著粒徑增大有減少的趨勢，與土石流洪峰流量呈現負相關，因此推測可能土方量受到洪峰流量影響。極端降雨下，未來複合災害的發生頻率將會增加。因此，我們必須從預防重於治療的方向入手。除了提出預防性治理措施外，還要定期對流域進行滾動式檢討，以減少災害的規模和風險。

關鍵字

氣候變遷；數值模擬； Hyper KANAKO模式；土石流

並列摘要

As a result of steep topography, young and weak geological formations, earthquakes, typhoon and heavy rainfall, much area in southern Taiwan are prone to the occurrence of disastrous mass movements such as debris flow disasters. Extreme heavy rainfall resulted from climate change induced serious sediment related disasters such as debris flow that caused an extremely dangerous disaster to the object of preservation. This study focused on the simulation of debris flow hazard and evaluation of governance engineering in Pingtung DF071. The results are explained as follows : We investigated the sediment environment and the location of disaster-prone areas of the study area. The survey results show that there are many landslides in the middle and upper reaches of the watershed and accumulations of sediment materials in some sections of the torrent. These sediment materials will endanger the security objects in the lower reaches of the torrent and the safety of No. 26 road. The two-dimensional debris flow model (Hyper KANAKO) developed by Kyoto University was used to simulate the flow situation of debris flow hazard in Pingtung DF071. The results show that the river cross sections of the torrent cannot pass the 50-year return periods. The governance countermeasure of DF071 is to divert the debris flow discharge. It is recommended to cross the no. 26 road by submerged or advanced engineering methods. The particle sizes of debris flow and deposition area of alluvial fan are discussed in this study. The result shows that the range of influence increases as the particle size increases, especially in a return period of less than 25 years. The occurrence frequency of compound disasters will increase in the future. Therefore, we must start from the direction that prevention is more important than treatment. In addition to proposing preventive treatment measures, we must also regularly conduct rolling reviews of the watershed to reduce the scale and risk of disasters.