Dentic flow – Wikipedia

The debris casting O debris flow ^[first] It is a type of landslide that consists of the movement towards the valley, along a side or in the throttle of a stream, of also deritical material of considerable size, usually accompanied by a considerable quantity of water, even if there are possible flows in dry material. The danger of debrical flows is due to their propagation speed and the remarkable impact force which, in case they take place in anthropized areas, are able to cause victims and reduce large buildings.

The debrical flows have high concentrations of detrital material, which moves to the valley along large distances with speeds varying from a few cm/s up to about 25 m/s (Sassa, 1987). The transported material has very variable granulometry and a single phenomenon manifests itself frequently with subsequent waves (pulses) due to temporary obstructions of the transport channel, and it is for this reason that these phenomena, in analogy with lava flows, also take the name of make torrentizie .

Deritical flows are phenomena widespread in most climatic bands, from desert to alpine regions and cover considerable importance both for their influence on the morphological evolution of the hydrographic basins in which they take place, and for the potential risk that determine on the flood , due to their high destructive capacity. In these areas, sudden increases in water availability, commonly due to intense rains such as summer thunderstorms or the rapid fusion of Nevai, can cause, with the sliding of the water along the slopes, the mobilization of large quantities of debris that form a detrital casting.

Deritical flows usually consist in mixture of water with fine grain soil (silt and clay) and/or coarse with high concentration, to which tree trunks and other vegetable debris are often associated. Thus an inconsistent mass of debrite is formed, supported and transported by the mass of water, without a clear separation between the solid and liquid phase. The behavior of a debrite flow can be assimilated to that of a non -Newtonian fluid, characterized by a variation of the resistance to the internal ring road not linearly proportional to the speed of the deformation itself. In some cases, moreover, the convective motions that develop within the casting together with the continuous impacts between the transported debris can keep the larger boulders collected along the route on the surface, which then focus on the top of the deposit, forming Characteristic deposits with inverse gradients of the granulometric distribution.

Traditionally, the following regimes are recognized in the flows (Takahashi, 1991):

• macroviscoso : the motion is slow and the sediments move in an orderly way (the interstitial fluid, however, is not necessarily in laminar motion);
• grain-inertial : in the presence of coarse material in high concentrations and high speeds – and therefore of a strong gradient of deformation of the mixture – the resulting behavior is governed by the collisions (a consequence is the so -called “reverse gradation” of the sediments);
• turbulent : typical for mixtures with high concentrations of cohesive material, the fluid can be represented in the first approximation with the Newtonian model but with a correction of the viscosity and possibly taking into consideration the threshold voltage (or yield strength );

However, the same flow can, during its path towards the valley, change its characteristics from one type to the other (E.G. The macroviscus regime is usually found during the stop phase).

Numerous models were also proposed in the literature to simulate the erosion and deposit rate for the propagation and arrest phase.