3D Simulation of Softrock Erosion in Chuoshui Creek

Abstract

This paper presents a study of soft rock erosion in Chuoshui Creek, Taiwan, using CCHE3D hydrodynamic model. The geological condition of Chuoshui Creek is complex; one reach of the river is flowing through a zone of base rock which is highly weathered and erodible, resulting in tremendous channel incision and headcut propagation particularly by high floods during typhoon seasons. A semi-empirical soft-rock erosion mechanism is implemented, in which the softrock properties, flow shear stress, and stream power, etc. are considered. The erosion rate coefficients of the formulation have been calibrated by field data in separate studies. In this study, the event of typhoon Morakot in 2012 was utilized to simulate the softrock erosion process in a 1.6km-long reach downstream of a large cross-river infrastructure, JiJi Weir, where serious soft rock erosion has occurred, threatening the integrity of the weir. The 3D model performed well under the conditions of highly unsteady, supercritical flows and complex channel topography. Comparing to the field data, the simulation results agreed well with the observations. The calibrated CCHE3D softrock model is then applied for evaluating the effectiveness of planned erosion control structures in the river.