圖書典藏及影音數位平台

台灣西部中央管河川之中下游多流經軟弱年輕地質區，該河川區域在受到自然環境變化的影響(如地震抬昇、氣候條件變遷等)或人為開發利用的影響(水利或交通設施的興建、砂石之開採等)下，已有多處軟弱岩質河床發生劇烈沖蝕或護甲層流失等現象。 由於軟岩抗侵蝕能力低，洪水作用下之沖蝕速率可能與硬岩相差達到一個數量級以上，快速的下切侵蝕作用可造成河川型態持續發生變化，造成河岸或人工構造物的不穩定進而發生破壞。因此，當河道型態轉變為由軟弱岩質河床的下切侵蝕主要控制時，往往轉變成河床下切之不可逆過程，必須充分掌握其沖蝕機制及沖蝕速率，方能進行適當的河川規劃治理。為掌握前述機制與沖蝕速率，除現場觀測資料分析外，數值模式為一不可或缺之工具，目前已有國外軟岩沖蝕模式之引進及初步應用，惟其模擬所採用的沖蝕模式之待定參數，大多藉由模式率定推得，並未透過實際調查或試驗獲得岩體材料參數；且模式引用機制之適用性仍有待進一步檢討研析。因此，爰成立本計畫，藉由沖蝕資料建置及沖蝕特性調查探討，進行模式研發，建立適合台灣河川之軟岩質河床沖蝕模式，以供未來治理規劃參考運用。

Owing to the effects of environmental changes (e.g., earthquake uplift, climate change, etc.) or human activities (e.g., hydraulic engineering, infrastructures construction, gravel mining, etc.), bedrock erosion and stream instability were induced in several major rivers of western Taiwan. Most of the major rivers in western Taiwan flow over the Western Foothills which are composed of weak sedimentary rocks. Once the weak rocks lost the protection from overlain armor layer, the channel bedrock erosion progressed rapidly. Moreover, morphological change is unidirectional and the rock removed from the bed lowers the base level of river bed. In order to offer the erosion behavior for properly managing the issue of rapid morphological change in river reaches, related research works on the subject of weak bedrock erosion were carried out in this three-year project. The severely eroded bedrock reach in both the Bazhang River and the Daan River were selected as study sites, which were chosen from the major rivers in western Taiwan after the comparison of their morphological change of bedrock erosive history and characteristics of bedrock erosion. The other three reaches at the Dahan River, the Dajia River, and the Jhuoshuei River were adopted as supplementary sites. The objectives of this project include: 1) proposing erosion mechanisms for weak bedrock erosion based on the erosion data of the studied reaches; 2) development of erosion rate model for weak rock riverbed; 3) development of erosion rate model for weak rock riverbank; 4) proposing guidelines for evaluation of bedrock scour and strategy suggestion for bedrock scour countermeasures.