當地震或是豪雨發生時，可能會伴隨著崩塌，而崩落的土石會阻塞住河道形成堰塞湖，在堰塞湖潰壩的過程中，底床位置會因為侵蝕堆積的關係產生劇烈的變化。本文將流體分成清水層、水砂混合層及可侵蝕底床層，其中我們將水砂混合層視為一剪力層，其濃度與底床並不相同，且本文將混合層與底床層的交界處視為一非物質奇異面，因此我們可以利用質量守恆以及動量守恆的不連續關係，並且配合邊界條件加上混合層底部的滑移速度做深度積分，來推導控制方程式，並且將侵蝕及堆積分開處理，再去觀察這些改變對流體的運移距離、流體厚度及侵蝕堆積率的影響。由於因為底床地形的曲率變化較大，故本文使用地形座標系統(Tai and Kuo, 2008;Tai et al. 2012)來描述流體在可侵蝕底床上的流動行為，而數值方法則使用具有shock-capturing特性的Non-Oscillatroy-Central(NOC) Scheme來模擬當潰壩發生時可侵蝕底床的變化，並且討論不同底部滑移速度和不同流場架構下對流體所造成的影響。
最後，結合地形座標系統與本文提出的侵蝕堆積機制以及底部滑移速度後再配合不同的濃度分布假設後，模擬的結果與實驗有相當程度的吻合，更可以支持本文所提出的理論。

When the earthquake or heavy rainfall occurs, it may induce collapse. The shattering rocks and soil would block the channel and form a natural dam. Then the barrier lake will be generated behind the natural dam. The basal surface will evolve intensely due to the erosion or deposition during the process of dam breaks. In present study, we consider the fluid as a three continuous layer, pure water, mixture transport, erodible bed layer. And we regard the mixture layer as a shear layer; its concentration is different with bed layer. The surface between the mixture layer and erodible bed is a non-material singular surface, so we can use the mass and momentum jump condition, which the bottom of mixture layer has a sliding velocity and depth-integrated to derive the government equation.
As the erosion and deposition have distinct mechanisms, we recommend that the erosion and deposition have to be treated separately. Then we can see the influence of these assumptions on the run-out zone, fluid thickness and the erosion/deposition rate.
Owing to the basal surface evolves intensely, in this paper, we use Unified Coordinate to describe the development of dam-break shear flow on deforming basal surface. For the numerical scheme, we use a shock-capturing non-oscillatory central (NOC) scheme to simulate the variation of basal surface, and discuss the influence of fluid on different sliding velocity and fluid configure.
Finally, we combine the Unified Coordinate, different concentration profile assumption, sliding velocity and new erosion mechanism. Our simulation had a good agreement with the experimental result, but the location of the boundary of transport layer and the bed is not precise enough, we postulate if we employ a diverse erosion equation and deposition equation, we may be able to correct this phenomenon and get a better result.

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