CCHE2D模式應用於蜿蜒複式河槽變遷之研究

Abstract

台灣的蜿蜒河川於汛期間，洪水漫過高灘地時，在兩岸堤防之間形成蜿蜒複式河槽，有關蜿蜒複式河槽主深槽變遷及河床沖淤方面需要更深入的分析。 本研究探討蜿蜒複式河槽溢岸流及未溢岸流對河道穩定及深槽變遷之影響。藉由二維動床模式CCHE2D模擬實驗室彎道試驗，了解二次流機制在彎道段之特性，並考慮岸壁沖刷機制，模擬正弦連續彎道河道側向變形過程；溢岸流的研究中，針對三組不同流量及不同上游來砂條件進行模擬，並應用於曾文溪下游之複式斷面河道，探討不同流況下整體河床沖淤趨勢，提供未來河川治理之參考。 實驗室及現地案例模擬結果皆與實測資料趨勢吻合。由溢岸流及未溢岸流之模擬結果可知，在未溢岸流情況下，深槽流量對主深槽之側向變形影響最大。當流量增加為滿灘流後，洪水平原流量愈大，深槽蜿蜒產生的離心力相對減弱，水流受蜿蜒深槽影響愈低。

Most of the main channels of alluvial rivers are meanders. The main channel becomes the compound channel confined by the embankments during rise of flood. Assessment of channel migration and bed erosion in meandering compound channel is necessary. The aim of this research is to investigate channel migration in meandering compound channel with inbank and overbank flows using CCHE2D model. Numerical simulations of two experimental bends show the characteristics of the secondary flow. Validations of the model, using sine-generated experimental data with bank erosion, have been performed. The model was also applied to study the morphological changes of experimental meandering compound channels and field case in Tseng-Wen Creek under changing conditions of flow and sediment. Good agreements between the simulated and available laboratory measurements were obtained. According to simulation results, the discharge in the main channel affects the stability of the main channel. The discharge in the floodplain of compound channel increases as the water depth increases, and the effect of the centrifugal force decreases. The results also point out the importance of the flow interaction between main channel and floodplain under overbank flow condition.