沖積河川上支流堰塞湖之形成與發展:理論及實驗

Abstract

本論文以理論配合實驗探討支流對沖積河道造成的影響，利用擴散理論的解析解來描述河床的反應，將理論預測的結果與實驗作定量的分析，並且與野外的河川剖面作定性的比較。從理論的預測與實驗的驗證得知，由支流匯入的沉積物對河道造成了兩種不同的反應，當匯流進河川的砂量較小或適量時，河川縱剖面將產生一個尖岬型的填積作用；當匯流進的砂量較大時，支流會阻斷主河道的輸砂並且在匯流口上游出現一個水域，水域範圍隨著支流持續的供砂而往上游繼續變大，形成了一個湖泊，填積作用在湖泊的上下游同時發展並且繼續維持自我相似的形狀，而湖泊的上游邊界會隨著湖水面上升自動向上游回朔，擴散理論運用在沖積河流的結果可以在小尺度的實驗與大尺度的現場河川中提供一個解釋的方法。

The response of alluvial rivers to the influence of tributaries is examined in the present thesis using a combination of theory and experiment. The river bed response is described using diffusion theory, and solutions are constructed using analytical methods. The predictions of the theory are then compared quantitatively against small-scale laboratory experiments, and qualitatively against documented river profiles. The theory predicts, and experiments confirm, that the river can respond in two different ways to a concentrated sediment influx from a tributary. When the influx is low to moderate, a cuspate aggradation of the long profile is obtained. When the influx is high, however, the river evolves a backwater region upstream of a tributary dam, interrupting sediment motion. The backwater region then grows into a tributary-dammed lake, maintaining a self-similar shape which co-evolves with upstream and downstream aggradation profiles. During lake growth, the upstream edge of the lake auto-retreats along a line of constant inclination. These results suggest that alluvial diffusion theory may help interpret both small-scale experiments and large-scale river processes.