淡水河流域及其出海口輸砂之三維數值模擬

Three-dimension hydrodynamics and sediment transport modeling of Danshui River

沈毅豪(Yi-Hao Shen)

指導教授 ： 周逸儒

國立臺灣大學/工學院/應用力學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201603707

摘要

本研究利用三維沿岸海洋模式SUNTANS來模擬淡水河懸浮泥砂動力行為，進行自由液面、鹽度入侵以及懸浮泥砂濃度之驗證，利用驗證完成之模式觀察河川中懸浮泥砂在水體之運動，並調查淡水河在平均流量以及高流量下河口最大混濁地帶(ETM)發生之位置。從平均流量以及高流量之模擬結果發現，兩流量條件下退潮所產生之鹽度垂直分層皆會將懸浮泥砂困住(trapped)在該處，使該處懸浮泥砂濃度上升，退潮時鹽度垂直分層處之紊流擴散係數較弱，以及該處之流場速度小不足以提供泥砂繼續傳輸，造成懸浮泥砂在鹽度垂直分層處發生沉積；而漲潮所產生之河口最大混濁之現象為將退潮所沉積之泥砂再懸浮所導致，此機制造成河口最大混濁地帶隨著潮汐來回移動。

關鍵字

淡水河 ； SUNTANS ； 河口最大混濁地帶 ； 鹽度密度分層 ； 泥沙困住現象

並列摘要

We apply a three-dimensional coastal model, SUNTANS, to study suspended sediment transport in Danshui River. First, the model is validated with the field measurement of water surface elevation, salinity, and suspended sediment concentration. Using the validated model to investigate the location of estuarine turbidity maximum (ETM) under different discharge conditions. Based on our results of two different discharge conditions, salinity stratification generated by ebb affects the turbulence diffusivity. Sediment is trapped in the location where the stratification takes place. Turbulence diffusivity and velocity are small at the location of stratification when the ebb occurs. The sediment from previous ebb is then resuspended when the flood occurs. This mechanism results in different locations of ETM in response to different tidal and discharge conditions.

並列關鍵字

Danshui River ； SUNTANS ； ETM ； Salinity stratification ； Sediment trapping

參考文獻

[2] Allen, J.I., Somefielf P.,Gilbert F.J., 2007. “Quantifying uncertainty in high-resolution coupled hydrodynamic-ecosystem models.” Journal of Marine Systems 64, 3-14.

[3] Amos, C.L., Daborn, G.R., Christian, H.A., Robertson, A., 1992. “In situ erosion measurements on fine-grained sediments from the Bay of Fundy.” Marine Geology, 108, 175-196.

[4] Bever, A. J. and C. K. Harris 2014. “Storm and fair-weather driven sediment-transport within Poverty Bay, New Zealand, evaluated using coupled numerical models.” Continental Shelf Research 86, 34-51.

[5] Bever, A. J., Harris, C.K., Sherwood, C.R., Signell, R.P., 2009. “Deposition and flux of sediment from the Po River, Italy: An idealized and wintertime numerical modeling study.” Marine Geology 260(1-4), 69-80.

[6] Bever, A.J., MacWilliams M.L., 2013. “Simulating sediment transport processes in San Pablo Bay using coupled hydrodynamic, wave, and sediment transport models.” Marine Geology 345, 235-253.