Predicting Rock Scour in an Alluvial River with a One-Dimensional Model

Taiwan rivers generally have steep slopes, are subject to high flows, have frequent earthquake activity, and have relatively weak bedrock. Bedrock is often exposed and rock scour is an important river process. For example, the river channel downstream of the Shih-Gang on the Tachia River experienced severe rock scour since the Chi-Chi earthquake of 1999 uplifted a portion of the river approximately 10 m. The occurrence of deep rock scour has been a major threat to river infrastructure at many other locations in Taiwan. In this study, a rock scour model is implemented into a one-dimensional (1D) hydraulic and sediment transport model. The rock scour model has components to predict the potential scour due to direct flow hydraulic forces and scour due to sediment abrasion. The resultant 1D model is capable of simulating the combined effects of rock erosion and alluvial river erosion and deposition. The new model is applied to the Tachia River in the reach affected by the Chi-Chi earthquake in 1999. Findings related to the applicability and limitations of the current rock scour models are reported.