近年來因全球氣候變遷導致高降雨強度事件頻率增加，而高降雨強度事件容易引發邊坡崩塌、土石流等事件，對於民眾及基礎建設造成嚴重損失。本研究使用小尺度三維渠槽進行實驗，藉由改變輸砂濃度及基準水面觀察沖積扇(alluvial fans)形態之變化，並搭配相機及雷射光，對沖積扇縱剖面、橫剖面、平面堆積形態、等高線、頂積層(topset)及前積層(foreset)角度以及流速剖面進行分析與討論。
控制參數包括顆粒粒徑、平台積水深及輸砂濃度，此輸砂濃度以水沙比(n)表示，水沙比為水入流量(Q_W)與顆粒入流量(Q_S)兩項比值。研究結果顯示頂積層角度主要隨平台積水深或水沙比增加而減少，成反比之關係；前積層角度隨平台積水深或水沙比增加而增加，成正比之關係。在有積水深實驗條件下，沖積扇形態明顯會因水體阻力而限制其堆積範圍；縱剖面形態會隨著平台積水深或水沙比增加而偏向於直線；橫剖面形態則是依不同斷面位置有所不同。但隨著積水深增加各組沖積扇實驗形態相似性也隨之提高。

關鍵字:沖積扇、基準水面、頂積層坡度、輸砂濃度

The depositional process of debris-flow fans is experimentally explored in this study. The fan slopes were controlled by particle sizes, sediment concentration(i.e., the ratio of sediment discharge (Q_S) to water discharge (Q_W)) and the base-level water depth. Both longitudinal and cross-sectional profiles of alluvial fans were simultaneously measured by using a digital camera, a reflection mirror and multi-laser settings. The top-set angles increases with the increasing sediment concentration, while decreases with the increasing base-level water depth. The longitudinal profile of the alluvial fan is concave when the base-level water is negligible. While the longitudinal profiles become linear, a milder slope for topset and a steeper one for the foreset, when the base-level water exists. The dimensionless cross-sectional profiles show self-similarity characteristics.

Key words: alluvial fans, base level, top-set slope, sediment concentration.

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