Experimental Formula for the Hydraulic Erosion Rate and Numerical Applications of Soft Bedrock Channels

Abstract

In this research, laboratory experiments and numerical models were used to develop a new formula for the hydraulic scour rate and a bedrock module for estimating soft bedrock erosion rate, and they were then applied in a study of the Zhuoshui River in Central Taiwan. From laboratory experiments, the relationship between the critical shear stress and hydraulic scour rate with the dominant bedrock property (uniaxial compressive strength) was established. For the soft bedrock module, only one parameter (i.e., the rock erodibility coefficient kv) was calibrated once the bedrock properties were known. An unsteady two-dimensional depth-averaged numerical model incorporating the new formula for hydraulic scour rate and the bedrock module was developed. After calibration and validation, the developed model well reproduced soft bedrock erosion during high-flow periods in this study reach. The simulation results showed that hydraulic scour is dominant in the upstream reach, while abrasive scour accounted for 65%–80% of the total erosion in the downstream reach. In addition, more bedrock erosion was observed at the locations with greater contributions from abrasive scour.