本文以實驗探討水流條件及滲流對沖積扇堆積型態之影響。實驗分為兩個部分，第一部分為沖積扇的堆積與形成過程；第二部分為乾沖積扇的滲流及破壞過程。第一部分實驗討論顆粒濃度對堆積型態及堆積歷程的影響。泥沙以恆定的供給率自儲存桶倉釋放，於輸送管內與定流量的水混合，並排入邊壁夾90度且底床水平的平台。第二部分討論在沖積扇張開90度，且無地表逕流的情形下，供水量與滲流高度的關係。先在平台堆放乾沖積扇，於扇頂處供應定流量的水，再透過嵌於邊壁玻璃管觀察各個徑向距離的水頭高。從實驗現象中發現，當顆粒的滲透係數太大時，滲流量將會影響堆積型態。當滲流量到達臨界值後造成顆粒孔隙不飽和，並使扇面留下皺褶，稱為「水砂分離」。決定「水砂分離」模式的關鍵在於水流的驅動力，而「水砂比(n)」以及「水流量(Q_s)」即是重要的參數。

The effect of sediment concentration and seepage on the formation of alluvial fans is experimentally explored in this study. Both the sediment and water are constantly supplied and mixed prior to being discharged into a platform with a horizontal angle of 90°. Firstly, the formation of alluvial fans with different sediment (coarse sand) concentrations and water discharges is examined. Secondly, the seepage-induced deposition and channel avulsion are observed on the fan surfaces during the evolution of the fan. As the fan apex grows to certain height, the downward seepage reduces the surface runoff on the fan surface. Consequently, the lobes or wrinkles rings appear on the fan surface and the fan slope abruptly increases. The sediment only accumulated at the unsaturated upper part of the fan, while the lower part of the fan remained steady and saturated. The key parameters controlling the fan slope are the sediment concentration, water discharge and the sediment characteristics (i.e., size and porosity).

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