Abstract:Earthquakes, landslides, mountain torrents can occur frequently in mountainous areas. During these events, a large number of particles can enter the river channel, causing abrupt changes of sediment supply. Due to varied sediment transportation capacity at different river reaches, sediments may be deposited and accumulated at some locations along the river, which leads to sharp increases of riverbed and water level. This poses a great threat to the prevention and control of water and sediment disasters in mountainous rivers. According to the field investigation of Baisha River and the Longxi River, boulder distribution can increase the river scouring and reduce the sediment deposition along the river banks. It can be seen that boulders can regulate the sediment supply in downstream river effectively. In this study, the characteristics of sediment transportation in a typical mountainous river under the influence of boulders have been analyzed via the CFD-DEM coupling method. In particular, the influences of sediment mass, flow rate and boulder spacing on the granular dynamics, sediment supply and water level along the mountainous river have been discussed. The numerical results show that boulders on the riverbanks can change the sediment transportation path. The debris particles typically move downstream along the middle of the river, which reduces the amount of sediment deposited on both sides of the river. Boulders can regulate the sediment supply in the lower reaches of the mountainous river by prolonging the time and reducing the flux of sediment transportation. As the boulders spacing and flow rate decrease and the debris mass from gully increases, the ‘catching’ efficiency of boulders will gradually increase. This effect can reduce the overall sediment deposition area in the mountainous river and keep the deposition location reasonably far away from the protected reach. Thus, a significant decrease of the water level along the protected reach can be achieved.