[1] Debris flows are often described as a succession of surges, which are characterized by enhanced peak depth and velocity and therefore by a tremendous increase of their destructive power. For given characteristics of the base flow, if the channel is sufficiently long to allow an appreciable wave development, the linear stability analysis in shallow streams is shown to provide a reasonable prediction of the critical flow condition and of the instability growth rate. The one-dimensional (1-D) theory, however, does not allow the determination of the wave period of the fastest growing perturbations. Debris waves most frequently develop following a mechanism similar to water roll waves: Instabilities grow up becoming clearly distinguishable waves, and then waves overtake one another with increasing wave period and amplitude. The typical hydrograph of a multiple-peak event is shown to be composed of a first surge, which is usually characterized by the highest depth, the longest duration, the greatest erosive power, and the most symmetrical shape, and of secondary waves that burst on the flow tail in the recession phase. The characteristics of the first surge can be explained by two different mechanisms. All waves that rise up near the flood crest run faster than this first surge and coalesce into it, causing its high depth and great volume. Moreover, segregation during the flow induces the concentration of boulders at the fronts, contributing to its depth enhancement, erosive power, and symmetrical shape. When a debris surge impacts a structure, the force pattern can be interpreted as the superposition of the reflection of the bouldery front and the formation of a vertical muddy jet due to the impact of the front wedge. Wave reflection can be described by a 1-D mass and momentum balance across the front, whereas the pressure impulse, due to the incompressibility of the interstitial fluid, can be analyzed through inviscid formulations validated for the representation of tsunami forces.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2005RG000175

Instability and surge development in debris flows

Post-analysis simulation of the collapse of an open sabo dam of steel pipes subjected to boulder laden debris flow

Although the latest statistics indicate a decrease in the number of victims of natural disasters in Japan, the number of sediment disasters has increased. A countermeasure against natural disasters...

https://journals.sagepub.com/doi/pdf/10.1177/2041419618789702

Method to evaluate the effect of inclination angle of steel open-type check dam on debris flow impact load:

Debris flows are a hazardous type of landslide, primarily caused by intense precipitation in steep mountainous terrain. Water, soil and debris mix to form a slurry that advances rapidly downslope, growing in size as it entrains more and more mass. They occur all over the world and are prevalent in canyons and steep gullies. They are considered to be one of the most dangerous landslide types, due poor predictability, a rapid onset, high mobility and high destructive powers. To investigate the flow behaviour of fine grain rich debris flow, rheological experiments and physical modeling has been conducted.The rheology has primarily been investigated using viscometer testing. Six viscometer tests were conducted. It was shown that fine grain rich soil material behaved as a shear thinning material exhibiting a yield strength, and could be modeled using Herschel-Bulkley rheology. 22 flume model tests were conducted using the same, fine grain rich material as for the viscometer tests. Velocities, flow heights and impact forces were measured and analysed. Two different soils were used, where the primary difference was the size of the clay fraction. Tests were conducted using different solid concentrations and quickness values. Coefficients for two simple hydraulic models (static and dynamic) were calculated from the results. The results indicate that the effect of variations in quickness value or solid concentration decreases as the flow volume is increased.The effect variations in quickness value appears to be complex. An extremum for the middle quickness value was observed in the velocity, flow height and impact force results. This implies that at least two effects are acting against each other when the quickness value is increased.

Model Testing and Rheology of a Fine Grain Rich Debris Flow

/pdf/effect-of-damaged-member-on-structural-robustness-of-steel-2c8k5ffc.pdf

Effect of Damaged Member on Structural Robustness of Steel Pipe Open Sabo Dam

The pressure of mud-debris flow acting on an obstacle was evaluated for cases in which the mud-debris flow was regarded as a non-compressible, then as a compressible fluid. In a non-compressible fluid, an equation of the fluid motion describes an equilibrium between pressure and potential rate. For a compressible fluid, the force is calculated by the density, impact velocity, and propagation velocity of pressure in the fluid. Analytical results showed that in a very few times, the force acting on a structure was some times the expected momentum value (per second)

Masahito Yoshizumi

Papers

Impact Force of Mud-Debris Flows Acting on Structure