Technical Studies


Study of erosion behavior of soft rock riverbed

In Taiwan, due to high flow rate, unexpected elevation changes, and inappropriate vegetation and development in floodplains, channel stability is always a devastating factor that leads to damages of main river channels and riverbanks. The sandy layer overlying riverbeds is usually disappeared after typhoon events, and soft rocks are exposed over riverbeds. Nowadays, most of sediment transport studies focus on channels with sand, silt or clay materials, and only few studies can be applied to the soft rock riverbeds. In this study, laboratory experiments and numerical models are developed to study erosion behavior of soft rock riverbed. The laboratory experiments mainly concentrate on the effects of hydraulic erosion and particle abrasion on soft rock scouring. For hydraulic erosion, experiments will be conducted in clear water and regression relationships between properties of soft-rock and hydraulic bottom shear stress will be established. In terms of particle abrasion, tests under different particle sizes and concentration will be carried out to find their correlations with riverbed erosion rates. The experimental results will be incorporated into the quasi-3D movable-bed numerical model to study sediment transport in practical cases. Comparisons of simulation results and the field data from several typhoon events will be presented. The outcome from this study is expected to use as guidelines for hydraulic engineers in the designing and planning and is valuable as a reference to future improvement projects.