臺灣博碩士論文加值系統

本論文主要研究目標為探討異重流三角洲於有限範圍中恆定條件與時變條件下的發展過程。藉由現地調查、水工模型實驗、理論及數值計算來分析整體形貌變化的情形。現地調查以位於台灣南投縣的霧社水庫作為研究案例，進行多次的野外縱剖面測量。為了模擬現地環境，我們利用單寬試驗水槽，配合傾斜岩石底床，以高密度鹽水模擬水庫異重流，並於下游設立可攔阻砂材但可使高密度流流出之網狀壩體，進行一系列水工模型試驗。並藉由影像分析方法得到異重流三角洲的形貌變化。在數值模擬部分，採用雙重擴散理論以及分別於水上水下率定的非線性水砂與坡度關係來模擬三角洲演進過程。最後將數值結果、實驗結果與現地現象進行比較，結果顯示，上游水砂條件顯著影響三角洲頂部(topset)的堆積角度，但對於三角洲前坡段(foreset)並不顯著；另一方面，下游水位控制三角洲河岸線(shoreline)位置並為坡度劇烈改變的基準。這兩種觀察結果於簡單條件(上游水砂及下游水位皆固定)與複雜條件(上游水砂及下游水位皆變化)下皆適用。另外當在水砂比大(Q/J>=30)時，水下三角洲會沿著前坡段產生砂波的現象，並隨著水位上升而出現更多的波段。

In this thesis, the main research goal is to study hyperpycnal delta progradation in finite length reservoirs, under both constant and time-varying boundary conditions. The upstream to downstream morphological evolution is analyzed using field investigation, laboratory experiments, and numerical modeling. For the field study, we investigated the Wushe Reservoir in Nantou County, Taiwan. The experiments were performed using a one-dimensional tank with inclined bedrock and a downstream mesh dam that traps sand while letting gravity currents flow out. For the numerical model, a two-diffusion theory was adopted, with calibrated non-linear transport relations along the topset and foreset. The results show that the upstream water and sand inflows influence greatly the topset slope, and the downstream water level evolution controls the location of the delta shoreline and the resulting slope break. Both observations apply in complex conditions (time-varying boundary conditions) as well as simple cases (constant boundary conditions). For large water and sand inflows (Q/J>=30), subaqueous sand waves form along the delta foreset.

致謝 i
中文摘要 ii
Abstract iii
Table of Contents iv
List of Figures vi
List of Tables xv
Chapter 1 Introduction …………………………………………………………...1
Chapter 2 Field Investigation …...…………………………………………...…...6
2.1 Study area ……………………………………………………………………...7
2.2 Reservoir observations ….…………………………………………………......8
2.3 Past evolution of Wushe Reservoir …………………………………………...11
2.4 Field survey methods……………. …………………………………………...20
2.5 Field survey results………………. …………………………………………..25
Chapter 3 Experiments and Measurement .....……………………………...….43
3.1 Experimental set-up ….……………………………………………………….44
3.2 Sand material …………….…………………………………………………...49
3.3 Experimental procedure ………….…………………………………………...52
3.4 Measuring method ………………. …………………………………………..54
Chapter 4 Theory and Numerical Model .…………………………………...…56
4.1 Governing equation ….……………………………………………………….57
4.2 Numerical computation: The finite volume method (FVM) …………….…...59
4.3 Calibration of sand transport relation ….……………………………………..61
Chapter 5 Results for Constant Boundary Conditions (Series A)………...….69
5.1 Low sediment transport rate (Run1)……………………………………….….72
5.2 Medium sediment transport rate (Run2)……………………………………...76
5.3 High sediment transport rate (Run3)…………………………………………78
5.4 Comparison between different transport rates ………………………………80
5.5 Comparison between experiment and simulation …...………………………83
Chapter 6 Results for Time-varying Boundary Conditions ……………...........89
6.1 Influence of varying water level (Series B) …….……………………………91
6.2 Influence of varying sediment supply (Series C) …………...……………….97
6.3 Influence of varying water supply (Series D) …………….………..……….103
6.4 Varying sediment supply with changing water level (Series E) ….............…118
6.5 Varying water supply with changing water level (Series F) ….………..……125
6.6 Comparison with field observations ……..………………………………….141
Conclusion …………………………………………………………………………...145
Reference ……………………………………………………………………………148

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