布唐布納斯溪支流沖積扇形貌動力學之研究：現地調查、理論與實驗之比較

Abstract

2009年莫拉克颱風在南台灣降下豪大雨，布唐布納斯溪狹帶了大量的土砂進入荖濃溪，被帶來的土石流受到兩側峽谷與對岸岩壁的限制，形成了拘限沖積扇。為了瞭解與模擬該區域堆積情況，本研究先以無人載具空中拍攝結合地面導線測量，調查高雄縣的荖濃溪與支流布唐布納斯溪匯流處土石流之形貌變化，分析歷年現地沖淤情況。接著，以現地資料建立的模型（黃建霖, 2014）模擬三種不同的情境。情境一，將實驗最簡化成只有支流渠道的堆積，並假設主流河道為水平，探討供砂點與沖積扇體積的關係；情境二，將支流河道供水、主流河道為水平；情境三，將主、支流河道供水，且主流河道非水平（黃建霖2014）。以堆積角理論擬合情境一，再將情境二、三結果與現地做對比。結果顯示，我們成功地利用理論去模擬拘束沖積扇的堆積過程，並且透過理論，了解到在有限條件之下，體積與起始點高程之間的關係。加上在沒有主支流的影響下，理論與實驗的結果吻合，比較之下可以發現，支流影響沖積扇面的不對稱，主流影響沖積扇面的不平滑，不論是主流或是支流，他們對於沖積扇的形貌都扮演著重要的角色。

Typhoon Morakot dropped heavy rain in southern Taiwan in 2009, and Pu-Tun-Pu-Nas River carried a large amount of sand into the Laonong River. The resulting debris flow is restricted by the canyons on both sides and the opposite wall, forming a confined debris fan.In order to understand and simulate the accumulation of this area, we used unmanned aerial vehicles combined with traverse survey to investigate the topography changes of Pu-Tun-Pu-Nas debris fan. Then using the model established by the local data (Huang, Chien-Lin, 2014). There are three different situations be simulated. First, the experiment is only debris fans to deposit in tributary channels, and the mainstream channel is assumed to be horizontal. The relationship between the apex and the volume of the alluvial fan will be discussed. Second, the channel of tributary supply water and the mainstream channel is assumed to be horizontal. Third, the tributaries and the mainstream occurred and mainstream channel is not horizontal (Huang, Chien-Lin, 2014). Using the theory of angles of deposit to fit the first situation, then compare the results of situation two and three with the field. The results show that the proportion of water and solid is very sensitive to the angle of deposit. We successfully used theory to simulate the aggradation of confined debris fans. Through experiment, we understand that whether it is the mainstream or the tributary, they play an important role in the appearance of the debris fan.