Abstract
The new waterway projects such as shortcut and gravel extractions have been carried out all over the country. The shortcuts have lowered river water surface elevation at the time of flood and they suppress the flooding. On the other hand, the riverbed elevations rapidly decrease due to bed slope changed artificially and canyons are formed in several rivers. However, little is known about how riverbed degradation occurs or how the canyon is formed by change of the bed slope. In this study, we conducted numerical simulations to evaluate the deformations of alluvial bed and peat bed in bed slope being changed. The results suggest that the bed slope become constant on the alluvial bed and the erosion proceeds at the bare peat bed, they also propose the upstream migration of the peat bed slope is what forms cyclic steps morphology. Moreover, we carried out numerical simulation of reproduction of Yubari river bed degradation by shortcut. We confirmed the possibility of the reproduction using the peat bed model.
