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. To accomplish the goal, the tasks in the first year of this three-year project include: (1)Literature review and data collection of river background. (2)Field investigation and measurement, including topographic survey, erosion phenomena of soft rock riverbed, riverbed erodibility, and bed rock erosion rate. (3)Study of the causes of riverbed erosion (4)Development of erosion mechanism, and empirical erosion rate in the study area. (5)Preliminary development of a mobile-bed model containing soft rock riverbed.