異重流三角洲於有限長度山谷中之地貌動力學研究：理論、實驗與現地調查

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。

關鍵字

異重流三角洲；水庫淤沙；水位變化；水工模型實驗；霧社水庫

並列摘要

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.

並列關鍵字

hyperpycnal delta ； reservoir sedimentation ； varying water level ； laboratory experiments ； Wushe Reservoir

參考文獻

Dietrich, W. E., Bellugi, D. G., Sklar, L. S., Stock, J. D., Heimsath, A. M., & Roering, J. J. (2003). Geomorphic transport laws for predicting landscape form and dynamics. Prediction in geomorphology, 103-132.

Fan, J., & Morris, G. L. (1992). Reservoir sedimentation. I: Delta and density current deposits. Journal of Hydraulic Engineering, 118(3), 354-369.

Kenyon, P. M., & Turcotte, D. L. (1985). Morphology of a delta prograding by bulk sediment transport. Geological Society of America Bulletin, 96(11), 1457-1465.

Kim, W., & Muto, T. (2007). Autogenic response of alluvial‐bedrock transition to base‐level variation: Experiment and theory. Journal of Geophysical Research: Earth Surface, 112(F3).

Kostic, S., Parker, G., & Marr, J. G. (2002). Role of turbidity currents in setting the foreset slope of clinoforms prograding into standing fresh water. Journal of Sedimentary Research, 72(3), 353-362.

國際替代計量

異重流三角洲於有限長度山谷中之地貌動力學研究：理論、實驗與現地調查

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