天然河川的泥砂運動長時間趨於動態平衡狀態，建於河道上的橋樑會破壞原有的平衡條件，引起一系列水理及輸砂特性變化，沖刷現象反應在現有橋墩造成額外沖刷量。本研究以NETSTARS V3.0現有功能為基礎，根據橋墩沖刷相關研究，撰寫橋墩沖刷功能程式並新增18個常用的橋墩沖刷公式於模式中。
為了瞭解新增橋墩沖刷功能之數值模式模擬台灣河川橋墩沖刷的可行性，本研究選擇中上游沖刷嚴重且下游淤積明顯的八掌溪流域厚生橋至觸口橋共48.4公里長河段。綜合水文、輸砂特性考量，模式在固床工、攔河堰斷面處設定不可沖刷，輸入邊界條件與現有19座橋樑資訊完成輸砂模式建置，分為一般沖刷與局部沖刷階段進行檢定，利用誤差評估參數檢視最佳參數以反應八掌溪流域河床變遷趨勢。一般沖刷參數檢定之結果為上游來砂量倍數=0.001；輸砂公式=Ackers & White (1973)；可沖刷層厚度參數=1；流管數=3，評估沖刷不足橋樑需進行局部沖刷之斷面進行參數檢定，局部沖刷參數檢定之結果為沖刷稽延時間=1500小時，橋墩沖刷公式=Jain and Fischer (1980)，經分析為交通部建議公式。
本研究以模擬成果進一步對未來十年八掌溪河床沖淤趨勢進行預測，推測有沖刷危害橋樑包括過水橋、永欽一號橋、吳鳳橋、五虎寮橋、觸口橋，共五座。研究成果可作為一維數值模式新增橋墩沖刷功能之參考。

River sediment transport tends to be in a state of dynamic equilibrium; however bridges built on the watercourse will destroy the original balanced conditions and cause a series of changes in characteristics of hydraulics and sediment transport. Moreover, additional erosions can be resulted from existing piers. This study applied NETSTARS V3.0 by adding the calculation functions of eighteen pier scour formulas based on comprehensive literature review to demonstrate local scour mechanisms.
In order to understand whether different scour formulas are applicable to bridges in Taiwan and the feasibility of numerical model in scour simulation, Pa-Chang River, which has severe bed degradation in upstream and obvious bed aggradation in downstream reach, is chose for this study. The study area is part of the river starting from the Housheng Bridge to the Chukou Bridge with the length of 48.4 km. Considering hydraulic changes and sediment transport, the river bed of where the groundsill works and weirs are located are set to be not washed. Simulations are conducted by setting boundary conditions and importing information of nineteen bridges, and validations are separated into two parts: general and local scour stages. The best parameters are qualified by EV_sediment for the changing tendency of whole Pa-Chang river basin. Simulation results of the general scour parameter test shows the best parameters of the ratep is 0.001; ised is Ackers & White; alt is 1 and stube is 3. The local scour simulations are made in regions where local scour is needed to be considered with the idurds 1500 hours and Jain and Fischer as ibrino.
Finally, long-term riverbed evolution is simulated, suggesting that there are five bridges at risk of erosion hazards, which are Guoshui Bridge, Yongqin NO.1 Bridge, Wufeng Bridge, Wuhuliao Bridge, Chukou Bridge. The result can be used as reference of one-dimensional numerical model which adds pier scouring functions.

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