Using Three-Dimensional CCHE3D Model to Study the Fluvial behavior – A Case Study of the Fengshan Creek basin of Taiwan

台灣受極端氣候影響，強降雨與颱風所帶來的洪水，容易造成河川沖刷甚至堤防潰堤，嚴重危害國人財產安全，因此致災性河段水理流況與輸砂現象實為重要課題。本研究選定新竹縣鳳山溪與霄裡溪匯流口之鳳山溪第34號大斷面至鳳山溪第27號大斷面作為研究區域，採用巢狀模擬觀念，在邊界條件採用集水區逕流模式HEC-HMS計算降雨事件之匯流點流量，再以集水區數值模式CAMP1DF模擬河道流況，計算全河段颱洪事件的水位、流速、流量等水理狀況，提供局部河段三維模擬之邊界條件；最後由CCHE3D輸砂模式模擬局部河段三維水深、流速及沖淤情形。另外本研究也進行現地流速量測與沖刷觀測，並與模擬結果比對。 CCHE3D在水槽試驗模擬方面，對於主深槽部分水深與流路模擬良好，但在玻璃水槽邊界沖刷上則有低估現象。杜鵑颱風(2015)事件模擬成果顯示，輸砂公式採用Wu et al. (2002)、底床粗糙度由植披分佈做不同設定、調適長度採用36m有較合理輸砂成果。模擬成果顯示因為固床工穩定河床，因此洪峰時期最大水深約為3.5m，約發生於第29號大斷面右岸處；另外一般河段表面流速約3~4m/s，固床工處流速約為5~6m/s；而沖刷位於固床工No3下游左岸，約有0.2~0.4m刷深，第29號大斷面約有0.1~0.2m刷深，第27.1~28號大斷面約0.1~0.15m刷深。本年度瑪莉亞颱風(2018)現地流量與沖刷觀測作業，洪峰流量約314cms，最高水位時，實測流速最高為2.7m/s，上升段流速靠左岸處較為混亂，在退水段流度呈現較為平滑且穩定，流速稍微高於洪峰時流速。流動式浮桶沖刷監測儀器無取得沖刷紀錄，顯示沖刷深度低於11cm。CCHE3D模擬瑪莉亞颱風之洪峰流速最大約為4m/s，而模擬沖刷成果為固床工No.3下游處左岸河道約0.1~0.3m刷深，另本河段也有零星0.1m沖刷，基本上與現地觀測結果相似。Taiwan has been suffered from extreme climate weather in recent years. Heavy rainfall or typhoon induced floods lead to severe erosion of riverbed, and further to result in levees broken. It causes seriously impacts of society safety and fortune. Therefore, the sediment transportation is an important issue for rivers in Taiwan. Cross sections from No.34 to No.27 of Fengshan River of Taiwan was selected as study site. A concept of nested modeling system is applied for necessary boundary control of local three-dimensional (3D) simulation. Surface runoff generated by HEC-HMS model is used as boundary input for river routing. Open channel model, CAMP1DF, is applied to obtain the river stage, velocity, and their discharge of entire river. And then the 3D hydraulic sediment transport model of CCHE3D is adopted to simulate local river hydraulics. The study also conducted field investigation to measure fluvial velocity, and set up electronic devices to attach the maximum riverbed erosions. Simulation indicated that CCHE3D performs well in the mainstream flow and its stage of experiment flume case. However, it revealed the slight underestimation of erosion especially to the locations close to the glass boundary. In the case of Typhoon Duaujn (2015), simulation showed a reasonable result by using Wu et al. (2002) as sediment transport formula, setting Manning coefficient according to the distribution of plants, adaption length equals to 36 m. Simulations also indicated the maximum water depth is about 3.5 m at section No.29. Fluvial velocity was about 3 - 4 m/s in general, but was about 5 - 6 m/s at the region of No. 3 ground work. The erosion occurred on the left side of the downstream of No. 3 ground work. It was about 0.2 - 0.4 m. On the other hand, the erosion on section No. 29 was about 0.1 - 0.2 m, and about 0.1 - 0.15 m from the other sections. The study has conducted field investigation during Typhoon Maria (2018). Discharge of flood peak was 314 cms, and maximum velocity was 2.7 m/s. Measurements indicated the fluvial velocity revealed some chaotic on the left side of channel in the rising limb. However, it showed relatively stable in the recession limb. It is noted that maximum fluvial velocity was occurred after flow peak. Float-out device detected no data in this event. It can be concluded that the maximum erosion was less than 11 cm of this case. Simulations of CCHE3D revealed that the velocity in flood peak was 4 m/s, and the relative severe erosion was around 0.1 - 0.3 m which occurred on the left side of No.3 ground work downstream. The rest of erosions were less than 0.1 m along the river. In short, simulations revealed similar pattern to the field measurements.摘要 i Abstract ii 目錄 iv 圖目錄 vi 表目錄 xii 符號表 xiii 第一章 緒論 1 1.1前言 1 1.2文獻回顧 1 1.2.1集水區模擬演算及水文數值模式 2 1.2.2河道動床模式 3 1.3研究架構 6 第二章 理論分析 8 2.1集水逕流模式HEC-HMS及集水區水文數值模式CAMP1DF 8 2.1.1HEC-HMS 模式介紹 8 2.1.2CAMP1DF集水區模擬演算 10 2.2CCHE3D數值模式 11 2.2.1CCHE3D水理模式理論 12 2.2.2CCHE3D輸砂模式理論 15 2-3現地量測方法 19 2.3.1流速觀測 19 2.3.2沖刷深度觀測 20 第三章 研究區域資料概述與概念模型建置 23 3.1研究區域 23 3.1.1地文資料概要 23 3.1.2水文氣象資料 24 3-2模擬環境建立 25 3.2.1HEC-HMS及CAMP1DF模式建立 25 3.2.2三維河道模擬建立 30 3.3現地量測配置 35 3.3.1河道斷面流速量測 35 3.3.2河床沖刷量測 38 第四章 結果與討論 40 4.1CCHE3D試驗室案例 40 4.2鳳山溪流域數值模式校準與驗證 44 4.2.1HEC-HMS及CAMP1DF成果 45 4.2.2CCHE3D敏感度分析及杜鵑颱風模擬成果 48 4.3現地量測與模式模擬分析 59 4.3.1巢狀模擬成果 59 4.3.2斷面流速量測情形 73 4.3.3底床沖刷量測情形 80 第五章 結論與建議 82 5.1結論 82 5.2建議 83 參考文獻 8