地形劇烈變化河道之沖蝕特性及其對河道穩定性的影響及治理策略-子計畫:複合岩床沖蝕模型之建置、標定及劇烈河道沖刷之模擬運用(I)

Abstract

台灣西部麓山帶河川中游出現之劇烈河床沖刷，往往發生於軟弱或節理發達之岩石河床上，岩石河床與沖積層的沖刷問題迥異之處在於（1）岩石河床下切一旦發生，就無法回復；（2）岩石河床抗沖蝕能力與沖蝕率與造成沖蝕之機制有極為密切之關係。就學理與分析法而言，岩石河床之沖刷機制與分析模型之相關研究仍未達成熟。 由實際案例顯示，欲考慮劇烈河道地形變化下之岩石河床沖刷問題，合理詮釋與模擬其現象，宜由不同尺度之主控機制出發。本計畫為整合型計畫「地形劇烈變化河道之沖蝕特性及其對河道穩定性的影響及治理策略」中的一個子計畫，期望基於前階段之微觀研究成果，試圖建構不同尺度之主控機制模型，配合其他子計畫河床野外地質調查成果，建構複合岩石河床沖蝕模型，模型參數擬經由啟發式最佳化運算策略標定之。模型之建構將以力學機制為基礎，將各種沖蝕機制之主控因素納入為模型主控變數。最終擬將多尺度複合模型移植入總計畫將發展之河道沖淤數模，以模擬河道發生劇烈地形變化後，描述造成劇烈岩石河床沖刷之內涵，目標在於詮釋受天然或人為原因之河道地形顯著改變後河道變遷之原因與過程。

Intensive river-bed erosion can take place in soft rock or heavily jointed rock mass. Unlike alluvial river bed, rock bed erosion is an irrecoverable process. The erodibility and erosion rate of rock bed are largely dependent of the mechanisms of rock erosion; these issues deserve more research. Field observation data reveals that there is usually a dominant mechanism controlling the rock-bed erosion; various mechanisms may be different in the scale of erosion. Accordingly, it should be more reasonable to establish multi-scale erosion models by taking into account the scale of erosion. The proposed project is a subsidiary project of the integrated project entitled “Erosion behavior of rock river-bed in the channel with drastic variation of longitudinal profile and its effects on the stability of river channel, and suggestion of counter measures for mitigating the erosion”. Based on field data and in-situ investigation results supported by other subsidiary projects, the proposed project aims to distinguish various rock erosion mechanisms by the scale of erosion. This project plans to explore major factors controlling each erosion mechanism and the criteria for each erosion mechanism to occur. Subsequently, erosion model for mechanisms corresponding to various scales of erosion (grain-scaled, block-scaled, and mass-scaled) will be established. Model parameters will be calibrated through heuristic optimization. These models then will be implemented into a computer code for sediment-transport simulation (this code will be developed in the main project of the integrated project). It is then possible to interpret the morphology variation in river channel by carrying out sediment-transport simulation.