當水流經過橋墩時於橋墩周圍會產生渦流現象，進而造成河床的沖刷，甚至危害橋墩的安全。然而台灣地區降雨型態具高強度及長延時之特性，因此形成數種形式的流量歷線，其對於橋墩周圍流場特性與沖刷將產生不同之影響。本研究利用三維數值模擬軟體(FLOW-3D)模擬橋墩周圍流場及沖刷之情形，首先以定量流流況下非均勻橋墩沖刷之模型試驗對FLOW-3D數值模式進行驗證，結果說明FLOW-3D數值模式可以合理模擬橋墩沖刷情形，並進一步探討定床與動床流場分布差異，其模擬結果顯示，動床配置下的流場分布可能受到動床變化影響，於橋墩周圍流速較小且較為混亂。此外，本研究針對不同流量歷線模擬橋墩周圍局部沖刷差異進行探討，其中流量歷線形式包含一種定量流、五種單峰型變量流(分為總水量相同與總延時相同)、三種多峰型變量流(其中兩種為雙峰型變量流)。根據單峰型模擬結果顯示，在總水量相同條件下，尖峰流量的大小將影響沖刷深度；總延時相同條件下，沖刷深度受總水量影響。接著本研究針對兩種不同尖峰流量之雙峰型變量流進行探討，高尖峰流量之組別在兩個峰值附近各沖刷約總沖刷深度的50%；低尖峰流量之組別則在到達第二個峰值附近方產生較大沖刷深度。最後多峰型變量流(固定總延時與總水量)的沖刷模擬結果顯示，達尖峰流量次數增加，河床最終沖刷深度也較大。雙峰型較單峰型變量流增加了總沖刷深度的22.1 %，但四峰型變量流之最終沖刷深度僅增加34.6 %，可能因流量超過泥砂臨界啟動速度時會產生一般沖刷之現象，造成沖刷過程中同時產生泥砂回填，此現象因達尖峰流量的次數增加而漸趨明顯，於第三個及第四個洪水波產生後各自回填了約總沖刷深度的2 %與17 %，且可能受到流量變化迅速影響，起始沖刷時間較單峰及雙峰型歷線延遲約30秒，至第三個尖峰流量產生時方有明顯下向刷深情形。

Taiwan is periodically disturbed by typhoon storms that usually characterize high intensity and long duration, causing different types of hydrograph in river channels influencing the characteristics of scours around bridge piers. This study used a three-dimensional fluid dynamics model (i.e., FLOW-3D) to simulate the characteristics of scouring around the bridge piers involved in various hydrographs.
As a result, the scour modeling around the bridge pier shows that the magnitude of discharge peaks and the amount of water discharges, respectively, control scour depth based on the same amount of water discharges and the same scouring duration. Moreover, the high double peaks cause 50% of total scour depth at each peak but the low double peaks generate significant scour depth only at the second peak. Moreover, based on the same simulation period (200s) and total water volume (1.28 m3), this study also simulated riverbed scouring affected by single, double and quadruple flood waves. Results indicate that the more the number of flood waves, the greater the scour depth; Moreover, quadruple flood waves lead to a factor of 1.35 increase in final scour depth under single flood wave; riverbed scouring always concentrates on the rising limbs for single or multiple flood waves. In addition, the forth flood wave of quadruple flood waves shows an evident sediment refill process (about 17%) on riverbed.

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