Soft Bedrock Erosion Modeling with a Two-Dimensional Model

Many rivers in Taiwan have steep slopes, are subject to typhoon induced flood flows, and contain soft bedrock that is weak and exposed at many locations. Soft bedrock erosion, therefore, is an important river process to consider for river projects. In this study, the bedrock erosion modeling is reviewed and a specific model is proposed by combining two existing models. The proposed bedrock erosion model is then incorporated into a two-dimensional mobile-bed model, SRH-2D. The model is used to simulate the bedrock erosion downstream of the Chi-Chi Weir on the Choshui River. A calibration study is carried out first to determine the appropriate values of the model parameters over a two and a half year period. The calibrated model is then used to predict bedrock erosion of the same reach for the next two years. Comparisons of both the calibration and verification model results with measured data lead to an assessment of the model performance. The study reports the current progress of bedrock erosion modeling; it also points to limitations and potential future research needs.