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Hyperconcentrated flow in nature and in practical application
Published in Zhaohui Wan, Zhaoyin Wang, Hyperconcentrated Flow, 2020
Debris flow is a kind of hyperconcentrated flow. It carries large amounts of granular particles with wide size composition, from large stones to clay particles, and its density may reach 1.9–2.2 g/cm3. The velocity of debris flow can be rather high. The maximun recorded velocity in China is 13.4 m/s (Zhang & Yuan, 1980). Hence it is a powerful destructive force and threatens railways, highways, lives and the property of local citizens. Volcanic debris flows and other hypercon-centrated flows resulting from them have been observed and studied by Scott & Dinehart (1985). Volcanic debris flows are named as lahars. And the hypercon-centrated streamflow following lahar is named as lahar-runout flow. Lahars are formed in the following ways: By the bulking of lake-breakout flood surges with eroded alluvium;From flood surges produced from snowmelt by hot lithic pyroclastic;From material catastrophically ejected and mixed with water of hydrothermal and glacial or snowmelt origin.
Modelling of hyperconcentrated flow in steep-sloped channels
Published in Journal of Hydraulic Research, 2018
Chien-Hua Chen, Ying-Tien Lin, Hau-Rong Chung, Te-Yung Hsieh, Jinn-Chuang Yang, Jau-Yau Lu
Hyperconcentrated flow usually occurs during intense rainfall events when large amounts of sediments brought from the upstream watershed result in an abrupt increase of sediment concentration in alluvial channels (Xu, 2002). Sediment transport induced by hyperconcentrated flow imposes significant impacts on river morphology and hydraulic structures (Wang, Qi, & Melching, 2009). Since the properties of hyperconcentrated flow, such as density and viscosity, are quite different than those of clear water flow, it cannot be treated as Newtonian fluid. In this study, hyperconcentrated flow is defined when its volumetric sediment concentration exceeds 2% (53 kg m–3), and therefore the fluid properties are subject to change in the model (Takahashi, 2014). In general, hyperconcentrated flow, mostly occurring in the upper reaches of the watershed, contains a substantial proportion of coarse sediment particles, so collision and friction between particles are expected (Takahashi, 2014). Coarse particles would deposit as the flow travels downstream and this region is defined as the motions of debris flows. As the debris flows move toward the downstream, the channel slope becomes milder and only fine particles suspend in the water column, where the inter-particle collision can be ignored. Wan and Wang (1994) defined this region as hyperconcentrated flow, also called immature debris flow. In this region, due to agglomeration of sediment particles, the flow becomes a non-Newtonian fluid, whereas the non-agglomerated particles still behave like Newtonian fluid. In this study, we focus on flow motions in this region.