高密度流形成之自我相似三角洲:理論及實驗

Self-similar delta formation by hyperpycnal flows: Theory and experiments

賴悅仁(Yueh-Jen Lai)

指導教授 ： 卡艾瑋

國立臺灣大學/工學院/土木工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.02524

摘要

當河川流入湖泊或水庫時，若河川的密度是高於湖泊，這時河川就會潛没入湖泊的底部形成異重流。 這種高密度流會導致三角洲的前部變成曲型曲線，而且三角洲前部的坡度也會小於安息角。 如同吉柏三角洲，高密度流三角洲也會依循著自我相似的結構而成長。 這本論文將會以實驗、理論及數值模擬的方式來探究由高密度流所形之自我相似三角洲。

我們將會以模型實驗來模擬高密度流三角洲的形成過程，並利用雙重擴散理論及坡度門檻值來描述三角洲形成的機制。對於變動湖水位的狀況，我們也提供了數值模擬的模式。最後，實驗、理論及數值模擬將會相互驗證。

關鍵字

三角洲 ； 濁流 ； 異重流 ； 自我相似 ； 解析解

並列摘要

From some field investigations (like Lake Constance and Lake Mead), the shape of a delta is not a Gilbert delta. Slope evolution between foreset and bottomset is not sharp but smooth. Delta foresets are not straight but curved. The appearances of turbidity currents were also observed. Turbidity currents are the subaqueous part of hyperpycnal flows. Hyperpycnal flows appear when a sediment loaded river flows into a lake (or a reservoir). The motion of these density currents leads the depositions at lake shore to form hyperpycnal deltas. Similar to the Gilbert delta, hyperpycnal deltas grow up in self-similar forms. In the thesis, some laboratory experiments were done to explore the processes of hyperpycnal deltas. Two-diffusion description with inclination thresholds were used to model those processes. Self-similar analytical solutions for hyperpycnal deltas were also solved to compare to other known analytical solutions of Gilbert deltas. Finally, experimental data, theory and numerical model were compared to each other.

並列關鍵字

delta ； turbidity current ； hyperpycnal flow ； self similar ； analytical solution

參考文獻

Boggs, S, Jr. (2006), Principle of sedimentology and stratigraphy, 4th Edition, Pearson Prentice Hall.

Adams, E.W., W. Schlager, and F.S. Anselmetti (2001), Morphology and curvature of delta slopes in Swiss lakes: lessons for the interpretation of clinoforms in seismic data, Sedimentology, 48, 661-679.

Begin, Z.B., D.F. Meyer, and S.A. Schumm (1981), Development of longitudinal profiles of alluvial channels in response to base level lowering, Earth Surf. Processes Landforms, 6, 49-68.

Bell, H.S. (1942), Density currents as agents for transporting sediments, J. Geology, 50, 512-547.

Capart, H., M. Bellal, and D.L. Young (2006), Self-similar evolution of semi-infinite alluvial channels with moving boundaries. J. Sedimentary Res., in press.