沖積扇演化與顆粒運動及沉積型態之模型實驗

Abstract

本論文的目的在於利用縮尺模型實驗研究沖積扇的發展。先將均勻混合粗細粒徑顆粒鋪設於於河床，並於表面挖一條引導用淺溝將水流導入。顆粒材料從河床流出並運移至平坦區並形成沖積扇。隨著時間的演進，水流切開沖積扇形成河道。以低中高三種不同的流量作為實驗條件，並詳細分析其結果。用三種影像方法記錄演變中地形與地層的結果。地形結果是用雷射掃描技術重複量測不同時間間隔的沖積扇。地層特徵則於實驗的最後將沖積扇用切片技術與照相建置。用粒子追蹤測速方法與移動照相機，追蹤水流中粗顆粒在河床上的移動。結合這三種方法的結果，可將最終沖積扇地形與地層連結，觀測在水流動中的河道演變。

The purpose of this thesis is to investigate the development of alluvial fans using small-scale laboratory experiments. The experiments start from a bed of uniformly mixed coarse and fine grains, with water flow confined to a pilot channel. Material incised from the bed is then transported to a flat area where an alluvial fan develops. Water flow over the fan splits into channels which evolve over time. Three experiments are analyzed in detail for conditions of low, medium, and high discharge. To document the resulting evolving morphology and stratigraphy, three imaging methods are used. Topography is measured at repeat intervals using a laser scan system. Stratigraphy is characterized at the end of each experiment by cutting and photographing transverse slices across the fan. During flow, particle tracking velocimetry is performed using a moving camera to track the motions of coarse grains over the bed. By combining results from these three methods, it is possible to relate the final fan topography and stratigraphy to observations of channel evolution during flow.