一維軟弱岩盤河道侵蝕數值模式之研發與應用

Abstract

國內目前對於河道沖蝕問題之探討，多侷限於沖積層河道，缺乏對岩石河床、岩石河岸之數模研究。當岩床或岩岸屬地質年代較年輕之岩層或弱面較發達之岩體，河道沖蝕問題往往甚為嚴重。國外對於岩床之沖蝕機制已累積不少成果，但實際將岩床沖蝕機制與河道動床數模整合者鮮少，目前常見一維動床數模如HEC-6、GSTARS、NETSTARS、CCHE1D等，皆尚未有軟岩侵蝕模擬之功能。 本研究藉由現有軟岩河道侵蝕模型，建構軟岩河道沖蝕模組，包括水力沖蝕與泥砂磨蝕兩種機制，由侵蝕模組計算獲得軟岩河床之侵蝕率與侵蝕量，結合EFA動床模式，建構具有可模擬軟岩侵蝕特性之一維動床數模。 本研究以假設案例測試軟岩侵蝕模組是否符合真實之物理特性，同時選取台灣大安溪為應用對象，以不同年份斷面資料進行檢定驗證，結果顯示EFA動床模式在結合軟岩河道侵蝕模組後，對於具有軟岩河床侵蝕特性之河川，可有良好河道變遷趨勢上之模擬預測。

In the present numerical study on channel migration, discussion and handling with incision of river course is mostly limited to alluvium rivers, lacking research for rock bed and banks. River incision is severe when rock bed and banks are young rock stratums or well developed joints. There are many achievements with erosion mechanisms of rock beds, but integration of erosion mechanisms with numerical models is few. Commonly seen numerical models like HEC-6, GSTARS, NETSTARS, and CCHE1D, do not have the capability to simulate soft bedrock erosion. This study relies on the development of soft bedrock river incision module, which include hydraulic scouring and sediment abrasion mechanisms. Soft bedrock incision module calculates soft bedrock incision rate and capacity. Combing the incision mechanisms with the EFA1D, a one dimensional numerical is developed to simulate soft bedrock incision phenomenon. This study first tests the physical factuality of soft bedrock incision model with fictitious cases. Furthermore, Ta-An River in Taiwan is selected as the study reach, and the cross sections measured in different years are used for the model calibration and validation. Simulation results show that river migration tendency can be well predicted after combining the soft bedrock incision module.