當顆粒鬆散的底床上發生潰壩時，由於侵蝕的發生會帶走底床上的土石；而當流體流速減緩或地形變化，土石亦會堆積於底床上。無論是侵蝕或堆積，底床會受流動層及底床層之含砂量變化而影響其演變。在本研究中，我們將流體分成上層清水層以及下層水砂混合層，而底床為水砂混合所構成之可侵蝕底床；其中我們將水砂混合層視為一層剪力層，且具備與底床不同的泥砂濃度。由於侵蝕或堆積的作用，底床隨時間劇烈變動，為能詳加探討底床演變對流體動態行為的影響。本研究透過地形座標系統 (Tai and Kuo, 2008; Tai et al. 2012) 來描述潰壩剪力流在可侵蝕底床上之動態行為，結合Non-Oscillation Central (NOC) 非震盪中央差分數值方法模擬理想狀況下發生潰壩時若底床為可侵蝕的流況，並探討不同的底床與流體泥砂濃度分布對流況及侵蝕堆積現象之影響。

When the dam-break flow occurs at the loose bed, due to the erosion, the sediment of the erodible bed will be taken away. Since the decreasing flow velocity and the influence of the topography, the sediment will be deposited on the bed. Either in erosion or by deposition, the basal surface evolves due to the sediment exchange through the interface between the flowing layer and the stagnant bed. In the present study, we combine a sharp-capturing, Riemann-solver-free non- oscillation central (NOC) scheme with Unified Coordinate method to describe the development of dam-break shear flow on deforming basal surface, and to discuss the influence of sediment concentration distribution of the bed and the flowing layer on erosion and the deposition. Consider a three-layer structure along the flow thickness, where a pure-water layer lies above a mixture layer of water and grains, and they flows over a water-saturated granular substratum. We postulate that the mixture transport layer is sheared and exhibits a discontinuity of sediment concentration at the interface between the mixture layer and the substratum. The numerical results show that our postulation is more consistent with the analysis of experiment.

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