主流河道侵蝕支流沖積扇端：理論、實驗與現地調查

Abstract

本論文主要的研究目的是探討主流侵蝕支流沖積扇端所造成的形貌變化。分為兩個部分，第一個部分，以台灣南部荖濃溪與布唐布納斯溪匯流處的沖積扇作為研究案例，進行河川縱坡面的測量及無人飛行載具的航拍。並比對地形資料以瞭解主流與堰塞湖對沖積扇端的影響。再依此設計實驗，以雷射掃描測量定量流下扇端的侵蝕情形；第二個部分參考實驗特徵，以艾克納方程式為基礎，建立一套數值模型，並依此模擬扇端演進過程。結果顯示，實驗及數值模型皆描述了扇端從下游向上侵蝕，且演進過程初期會有一坎崖與溢流口位置相異。而在現地與實驗皆觀察到會有下游沖積扇在扇端產生並向上游遞進，其可以保護扇端不被侵蝕並造成潰壩過程停止。

The main purpose of this thesis is to research the morphological changes caused by the trunk river erosion of a tributary fan margin. In the first part, the debris fan at the confluence of Laonong River and Pu-Tun-Pu-Nas tributary in southern Taiwan is taken as a case study. The long profile of the river and aerial photographs of UAV are carried out. And the topographic data are compared to understand the influence of the trunk river and the dammed lake on the debris fan margin. Based on this, the experiment is designed to measure the erosion of fan margin under the condition of constant flow rate by laser scanning. The second part use the experimental observations to construct a numerical model of the process based on the Exner equation. The model is then used to simulate the evolution process of the fan margin. The results show that both the experimental and numerical models describe the erosion from downstream to upward at the fan margin, and there will be a head cut scarp at the beginning of the evolution process which is distinct from the location of the outflow crest. Downstream alluvial fans are observed both in situ and in experiments to form downstream of the fan and retreat upstream, which can protect the fan margin from erosion and stop the process of dam failure.