Geometrical Characterization of Sediment Deposits at the Confluence of Mountain Streams

Abstract

Debris flow injections from tributaries into a main mountain stream generate deposits of sediments which, in turn, result in obstruction and eventual damming of the river section. This contribution presents the results of a series of flume experiments on the dynamics of these deposits, with reference to three different types of blockage: no blockage, partial blockage, and full blockage. Results show that the shape of the deposit is mainly controlled by the ratio between the debris flow discharge and the main river discharge. The experimental dataset is used to develop a deposit resilience stability index based on the shape of the deposit contour retrieved from photos taken from above. The proposed index is based on the invariant elliptic Fourier coefficients and the dimensionless transverse obstruction parameter. The elliptic Fourier coefficients give information on the symmetry of the deposit contour. High symmetry indicates more stable and resilient deposits. The proposed index is calibrated on the basis of the flume experiments and tested with field data. The results are quite promising and suggest that the index can be appropriate for a fast hazard assessment of multiple debris flow deposits at a regional scale.

Contribution of Excessive Supply of Solid Material to a Runoff-Generated Debris Flow during Its Routing Along a Gully and Its Impact on the Downstream Village with Blockage Effects

“…The slope in this area is sufficiently steep for the generation of large scale surface runoff, implying a significant amount of gravitational energy. As such, the The dynamics of the propagating surge is a function of different parameters, including the sediment content, channel slope angle and run off [54]. As shown in Figure 11, the common types of natural topography that are favorable for the blockage of debris flows included (i) the constricted section of gully channel, (ii) arc gully channels and (iii) the intersections between the gully channels of different longitudinal gradients.…”

A modeling methodology to study the tributary-junction alluvial fan connectivity during a debris flow event

“…The momentum ratio is calculated as the product of the flow rate ratio R Q , the velocity ratio R V , the bulk density ratio R γ and the confluent angle Dang et al (2009) proposed a critical index C = R M S C for dam formation with different partial and complete blockage thresholds. Stancanelli and Musumeci (2018) highlighted that the thresholds have to be calibrated depending on the material adopted. For gravel deposits, they proposed a threshold value of C = 9.…”

Comment on nhess-2021-266

“…Dang et al (2009) proposed a critical index C = R M S C for dam formation with different partial and complete blockage thresholds. Stancanelli and Musumeci (2018) highlighted that the thresholds have to be calibrated depending on the material adopted. For gravel deposits, they proposed a threshold value of C = 9.…”