Rapid Erosion Process of Soft Rock Riverbed — The Taan River as An Example (2/3)
The phenomena of severe erosion over riverbed can be found in several major rivers of Taiwan in recent years. Continuous terrain variation of main channel by rapid riverbed erosion could be a great challenge to the function and safety of infrastructures over river, and the ecology environment of river, etc. The countermeasure to deal with rapid bedrock erosion is an urgent requirement. The project aims to realize the process of bedrock erosion, to propose a bedrock erosion model, and to develop a mobile-bed model with soft rock riverbed. The channel uplifted (maximum 10 meters vertically) by the 1999 Chi-Chi earthquake in the Ta-An River, which length is 1km in longitudinal direction and 500 meters in lateral direction, is choosing as the study site. In the third year of this three-year project, the scope includes the followings: (1) site investigation and erosion measurement (including river cross-sections survey, topographic survey via LiDAR, monitoring bedrock erosion by erosion pins and photogrammetric, etc. ); (2) development of an in-situ operating procedure for monitoring the potential locations of bedrock erosion in river bed; (3) laboratory tests for rock physical and mechanical properties, such as slake durability index, uniaxial compressive strength, triaxial shear strength, direct shear strength and tensile strength; (4) evaluation of rock bank stability and stable channel width for the uplift section; (5) evaluation of flood-prevention capability of present embankment; (6) the validation of the proposed bedrock erosion rate model and the computer program with the function of mobile-bed simulation, and predicting the long term channel variation through the mobile-bed simulation.