Role of baffle shape on debris flow impact in step-pool channel: an SPH study
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Shuai Li I Chong Peng I Wei Wu I Shun Wang I Xiaoqing Chen I Jiangang Chen I Gordon G. D. Zhou I Bhargav K. Chitneedi
Role of baffle shape on debris flow impact in step-pool channel: an SPH study
Abstract Drainage channels with step-pool system are widely used to control debris flow. The blocking of debris flow often gives rise to local damage at the steps and baffles. Hence, the estimation of impact force of debris flow is crucial for designing step-pool channel. Existing empirical models for impact pressure prediction cannot consider the influence of baffle shape. In this work, a threedimensional smoothed particle hydrodynamics (SPH) study on the impact behavior of debris flows in step-pool systems is presented, where debris material is modeled using the regularized Bingham model. The SPH method is first checked using the results from two laboratory tests. Then, it is used to investigate the influence of baffle shape and flow density. Numerical results show that the impact pressure at the first baffle highly depends on the baffle shape; however, the largest impact pressure usually occurs at subsequent baffles due to the violent impact induced by jet flows. The peak impact pressure at the first baffle initially grows with increasing flow density; however, it starts to drop as density is beyond a threshold. Based on the numerical results, an empirical relation considering the influence of baffle shape is proposed for better prediction of debris impact pressure. Keywords Debris flow . Impact pressure . Step-pool systems . Baffle configuration . Smoothed particle hydrodynamics Introduction The step-pool bed configuration, a common geomorphologic phenomenon in high-gradient mountainous terrain (3–30%), consists of a sequence of steps and pools forming a staircase-like structure in longitudinal profiles (Chin 1999; Waters and Curran 2012).This self-organized system can enhance channel bed resistance, slow down mass flows, and effectively dissipate flow energy (Maxwell et al. 2001; Wilcox et al. 2011). Inspired by this interesting phenomenon in natural stream flow, similar protection systems with step-pools were introduced to mitigate debris flow (Yu et al. 2007; Wang et al. 2012). For instance, Wang et al. (2012) reported an experiment on debris flow on artificial step-pool system. It was found that the step-pool system can result in increased energy dissipation; thus, it reduces the erosion of gully bed and the risk of debris flow outbreak. Debris-flow drainage channels are important hazard mitigation infrastructure because they are usually constructed in the headwaters of deposit fan, where the life lines are susceptible to debris flow hazards. On the other hand, the analogy between step-pool sequences and energy dissipation structures stimulates the investigation of artificial step-pool in drainage channels. A number of studies were carried out to understand the transport processes of debris flow in drainage channel with artificial step-pools (Chen et al. 2009, 2015, 2018; Huang et al. 2009; Liu et al. 2016). These
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