Vol16 No.6: 1367-1380
【Title】Dynamics of loose granular flow and its subsequent deposition in a narrow mountainous river
【Author】LEI Ming; XU Ze-xing; ZHAO Tao; WANG Xie-kang*
【Addresses】State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China
【Corresponding author】WANG Xie-kang
【Citation】Lei M, Xu ZX, Zhao T, et al. (2019) Dynamics of loose granular flow and its subsequent deposition in a narrow mountainous river. Journal of Mountain Science 16(6). https://doi.org/10.1007/s11629-018-5080-5
【Abstract】A large amount of loose debris materials were deposited on the slope of mountainous areas after the 2008 Ms 8.0 Wenchuan earthquake. During and after the earthquake, these loose debris deposits collapsed and slide into valleys or rivers, changing river sediment supply condition and channel morphology. To investigate the mechanisms of granular flow and deposition, the dynamics of slope failure and sediment transportation in typical mountainous rivers of different intersection angles were analyzed with a coupling model of Computational Fluid Dynamics and Discrete Element Method (CFD-DEM). The numerical results show that the change of intersection angle between the granular flow flume and the river channel can affect the deposit geometry and the fluid flow field significantly. As the intersection angle increases, the granular velocity perpendicular to the river channel increases, while the granular velocity parallel to the river channel decreases gradually. Compared to the test of dry granular flow, the CFD-DEM coupling tests show much higher granular velocity and larger volume of sediments entrained in the river. Due to the river flow, particles located at the edge of the deposition will move downstream gradually and the main section of sediments deposition moves from the center to the edge of the river channel. As a result, sediment supply in the downstream river will distribute unevenly. Under the erosion of fluid flow, the proportion of fine particles increases, whilethe proportion of coarse particles decreases gradually in the sediment deposition. The build-up of accumulated sediment mass will cause a significant increase in water level in the river channel, thus creating serious flooding hazard in mountainous rivers.
【Keywords】Loose debris materials; Sediment supply; CFD-DEM coupling method; Numerical simulations