莫拉克颱風對公路特定路段災害探討暨對策擬定之研究

中度颱風莫拉克於民國98年8月8日挾帶超大豪雨量侵襲台灣，引發台灣中南部及東南部地區發生水患及土石流，道路柔腸寸斷，為台灣自民國48年年八七水災以來最嚴重的水患災害。台20線（包括位於山區的南橫公路）為高雄桃源區勤和~復興段對外主要聯繫道路，受到中度颱風莫拉克豪雨影響，荖濃溪暴漲挾帶上游支系崩塌源的土石及匯聚布唐布那斯溪巨量土石流，造成本路段勤和明隧道完全覆滅，更使得多處道路橋梁遭沖毀。經本研究近期於民國101年3月至6月間之調查發現荖濃溪河域附近撒拉啊塢橋等橋梁橋墩情況，其土石再次淤高，而位在上處復興部落的復興橋險將覆沒，顯示荖濃溪桃源河段及支系溪床無論上游或下游處，皆非常不穩定，目前僅能以臨河底便道及鋼便橋維持基本交通需求。接著本研究即是針對這區域路段（台20線95k~103k）探討災害發生原因，並提供防範對策之擬定，考量層面包括河域對策、汛期對外交通對策、非汛期對策、工程對策、長期復建對策等項，發現到河道淤積造成河向改變逐漸嚴重危害威脅沿線村里部落安全，最後經本研究期能從所探討之研究結果對未來該路段之交通及當地居住安全有所助益。

關鍵字

莫拉克颱風；災害；超大豪雨；臨河便道；鋼便橋；土石流；對策

並列摘要

On 8th August of 2009, carrying extreme torrential rain within a short period of time, the landfall of Typhoon Morakot caused severe floods and mudslides at central, south and southeast of Taiwan with consequent severe damages to many sections of highways at remote mountain area. This is the worst catastrophic storm experienced since the severe flood caused by Typhoon Ellen on 7th August of 1959. Tai-20 highway provides major connection with outside world for the remote Cinhe~Fuxing section of Taoyuan District, Kaohsiung city. Due to the extreme torrential rain, flush flood at Laonong Creek carrying huge amount of mud from mudslides within its tributary and Butangbunasi creek caused serious damaged to this section of highway resulting complete covered up of the Cinheming tunnel by mudslide. Many sections of Tai-20 highway and bridges were flushed away by floods. Investigations were conducted recently from March to June of 2012 for bridge column conditions of bridged within this section of Laonong creek including Salaahwu Bridge. The results showing that the stratum of the creek elevated again, and the Fuxing Bridge located in Fuxing tribal community was nearly buried by depositions. These evidence showing that the stratum at upstream as well as at downstream of Taoyuan section of Laonong Creek and its estuary are unstable. Currently only minimal transportation functions are sustained via temporary road constructed within riverbed and temporary steel bridges. This study is to explore fundamental causes of these types of catastrophic damages to this section of the highway (Tai20 highway 95k-103k) in order to establish countermeasure strategies in consideration of watershed management, transportation strategy for flood and non-flood seasons etc. and long-term rehabilitation strategies to reach the ultimate goal of all time safe highway system. The phenomenon of flow path changes caused by deposition eventually become a serious threat to properties and lives of villages along the river banks is discovered and it is to anticipate the results from this study will benefit protection of the highway and residents at vicinity.