潰壩過程中底床載及流量歷線之實驗量測

本論文使用小尺度實驗模擬潰壩過程中流量及底床載之互動關係。在等寬的渠道且單一粗糙顆粒鋪成三角壩的條件下，變換上游不同湖的面積來模擬，使用影像處理分析結果。整體潰壩的量測包括水位歷線和壩體隨時間的變化，另一方面小範圍量測包括在不同斷面不同時間的速度和粒子濃度曲線以及不同地方的底床載運移層。濃度曲線根據最近發展而成的雷射條紋濃度量測，此方法是利用雷射量測粒子離牆壁的距離。結合不同次實驗和時間同步化，可以得到在潰壩時完整的流量歷線和輸砂量歷線。小範圍在不同斷面的結果可以用運動層結構來解釋。儘管水流不是均勻流，但是底床載運移層的速度跟較上層的底床載運有關。利用簡單的數學潰壩模式來了解實驗結果，並且跟野外資料做比較。新的數學模式和實驗結果吻合，但現地資料的流量歷線仍然是比模式狹窄。

關鍵字

潰壩；小尺度實驗；底床載運；粒子速度測量追蹤；雷射條紋濃度量測

並列摘要

Dam breaching is one of the most dangerous combination of water flow and sediment motion that can occur. In this thesis, a simplified version of this phenomenon is examined in small-scale laboratory experiments. Triangular dams composed of single size coarse grains are considered, in a channel of constant width, varying the area of the upstream lake. Imaging methods are used to acquire both global and local measurements of the dam breaching flows. Global measurements include lake level hydrographs and evolving longitudinal dam profiles. Local measurements, on the other hand, include time-dependent vertical profiles of velocity and granular concentration at different cross sections, capturing the spatial development of the bed-load transport layer. The concentration profile is acquired using a recently developed method based on measuring the granular distance from the wall using a laser light sheet. By combining and synchronizing the different methods, it is possible to record water and sediment discharge hydrographs over the course of a complete dam breaching event. Local results are interpreted in terms of transport layer structure. Water flow is non-uniform, but the bed-load transport layer adjusts to the flow velocity along the upper interface of the layer. Global results are interpreted with the aid of simple mathematical models of dam breaching, and compared with data from field events. A new simple model of dam breaching is proposed, yielding better agreement with experimental data. Nevertheless, field hydrographs remained narrower than predicted.

並列關鍵字

dam breaching ； small-scale experiments ； bed-load transport ； particle tracking velocimetry ； laser stripe concentration measurements

參考文獻

Liu, N., Chen, Z., Zhang, J., Lin, W., Chen, W., & Xu, W. (2010). Draining the Tangjiashan Barrier Lake. Journal of Hydraulic Engineering, 136, 914-923.

Capart, H. (2013). Analytical solutions for gradual dam breaching and downstream river flooding. Water Resources Research, 49 , 1968-1987.

Capart, H., & Fraccarollo, L. (2011). Transport layer structure in intense bed-load. Geophysical Research Letters, 38, L20402.

Capart, H., Young, D. L., & Zech, Y. (2002). Voronoi imaging methods for measurement of granular flows. Experiments in Fluids,1 ,121-135.

Hering, F., Leue, C., Wierzimok, D., & Jahne, B. (1997). Particle tracking velocimetry beneath water waves. Part I:visualization and tracking algorithms. Experiments in Fluids, 23, 472-482.

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潰壩過程中底床載及流量歷線之實驗量測

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