Superelevation of flowing avalanches around curved channel bends

McClung, D. M.

doi:10.1029/2001jb000266

Cited by 30 publications

(24 citation statements)

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“…Based on the results of large-scale flume experiments, back-calculation using superelevation may presently be the most accurate way to estimate debris flow velocity (Iverson et al 1994). The most commonly referenced method for making this estimation is the forced vortex equation (Chow 1959;Henderson 1966;Hungr et al 1984;Johnson 1984), which equates fluid pressure to centrifugal force (McClung 2001):…”

Section: Introductionmentioning

confidence: 99%

A study of methods to estimate debris flow velocity

et al. 2008

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Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow channel or predicted using flow equations that require the selection of appropriate rheological models and material property inputs. This research investigated difficulties associated with the use of these conventional velocity estimation methods. Radii of curvature estimates were found to vary with the extent of the channel investigated and with the scale of the media used, and back-calculated velocities varied among different investigated locations along a channel. Distinct populations of Bingham properties were found to exist between those measured by laboratory tests and those backcalculated from field data; thus, laboratory-obtained values would not be representative of field-scale debris flow behavior. To avoid these difficulties with conventional methods, a new preliminary velocity estimation method is presented that statistically relates flow velocity to the channel slope and the flow depth. This method presents ranges of reasonable velocity predictions based on 30 previously measured velocities.

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Section: Introductionmentioning

confidence: 99%

A study of methods to estimate debris flow velocity

et al. 2008

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“…(7), it is necessary to correct for the downslope component of the gravity vector. Therefore, the slope normal component of gravity (g*) is used, when considering the pressure in the force balance on a plane normal to the flow direction (McClung 2001). Johnson and Rodine (1984) consider g* to be relevant for channel slopes exceeding approximately 15°.…”

Section: Forced Vortex Equation Adapted To Debris Flowsmentioning

confidence: 99%

“…Superelevation can be observed in curved channels, where the flow height along the inner curve is lower than the flow height along the outer curve, caused by the centrifugal acceleration of the flow. This semiempirical method is described as a vortex or forced vortex method (Apmann 1973;Costa 1984;Hungr et al 1984;Chow 1988;McClung 2001;Prochaska et al 2008). This approach assumes a constant radius, determined from the center line of the channel bend.…”

Section: Introductionmentioning

confidence: 99%

Debris-flow velocities and superelevation in a curved laboratory channel

2015

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Abstract:The vortex equation is often used to estimate the front velocity of debris flows using the lateral slope of the flow surface through a channel bend of a given radius. Here we report on laboratory experiments evaluating the application of the vortex equation to channelized debris flows. Systematic laboratory experiments were conducted in a 8 m long laboratory flume with a roughened bed, semi-circular cross section (top width 17 cm), and two different bend radii (1.0 and 1.5 m) with a common bend angle of 60°, and two channel inclinations (15°and 20°). Four sediment mixtures were used with systematic variations in the amount of fine sediment. In the experiments, 12 kg of water-saturated debris were released in a dam-break fashion, and multiple experiments were conducted to verify the repeatability for a given sediment mixture. Data are available for 69 experimental releases at a channel inclination of 20°and 16 releases at an inclination of 15°. Flow velocity was determined with high-speed video, and flow depth and the lateral inclination of the flow surface (superelevation) were measured using laser sensors. In general, the results from an individual sediment mixture are repeatable. We found that the channel slope as well as centerline radius have a significant influence on the correction factor k used in the vortex equation. Relatively coarse-grained sediment mixtures have larger superelevation angles than finer-grained mixtures. We found a statistically significant relation between the correction factor and Froude number. Correction factors of 1 < k < 5 were found for supercritical flow conditions. However, for subcritical flow conditions the correction factor shows a larger value as a function of the Froude number, which leads to an adaption of the forced vortex formula considering active and passive earth pressures. Finally, based on our experimental results, we present a forced vortex equation for debris-flow velocity estimation without a correction factor. Mots-clés : coulée de débris, vitesse de front de coulée, inclinaison latérale, modèle physique, équation de vortex force.

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“…The level of flowing material is higher on the outward side than on the inward side. This can provide information on mean velocity at that location [228,133,168].…”

Section: Using Historical or Monitored Eventsmentioning

confidence: 99%

Plasticity and geophysical flows: A review

Ancey

2007

Journal of Non-Newtonian Fluid Mechanics

349

277

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The objective of this review is to examine how the concept of plasticity is used in geophysical fluid dynamics. Rapid mass movements such as snow avalanches or debris flows involve slurries of solid particles (ice, boulder, clay, etc.) within an interstitial fluid (air, water). The bulk behavior of these materials has often been modeled as plastic materials, i.e., a plastic material yields and starts to flow once its stress state has significantly departed from equilibrium. Two plastic theories are of common use in fluid dynamics: Coulomb plasticity and viscoplasticity. These theories have little in common, since ideal Coulomb materials are two-phase materials for which pore pressure and friction play the key role in the bulk dynamics, whereas viscoplastic materials (e.g., Bingham fluids) typically behave as single-phase fluids on the macroscopic scale and exhibit a viscous behavior after yielding. Determining the rheological behavior of geophysical materials remains difficult because they encompass coarse, irregular particles over a very wide range of size. Consequently, the true nature of plastic behavior for geophysical flows is still vigorously debated. In this review, we first set out the continuum-mechanics principles used for describing plastic behavior. The notion of yield surface rather than yield stress is emphasized in order to better understand how tensorial constitutive equations can be derived from experimental data. The notion of single-phase or two-phase behaviors on the macroscopic scale is then examined using a microstructural analysis on idealized suspensions of spheres within a Newtonian fluid; for these suspensions, the single-phase approximation is valid only at very high or low Stokes numbers. Within this framework, the bulk stress tensor can also be constructed, which makes it possible to give a physical interpretation to yield stress. Most of the time, depending on the bulk properties (especially, particle size) and flow features, bulk behavior is either Coulomb-like or viscoplastic in simple-shear experiments. The consequences of the rheological properties on the flow features are also examined. Some remarkable properties of the governing equations describing thin layers flowing down inclined surfaces are discussed. Finally, the question of parameter fitting is tackled: since rheological properties cannot be measured directly in most cases, they must be evaluated from field data. As an example, we show that the Coulomb model successfully captures the main traits of avalanche motion, but statistical analysis demonstrates that the probability distribution of the friction coefficient is not universal.

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Superelevation of flowing avalanches around curved channel bends

Cited by 30 publications

References 24 publications

A study of methods to estimate debris flow velocity

A study of methods to estimate debris flow velocity

Debris-flow velocities and superelevation in a curved laboratory channel

Plasticity and geophysical flows: A review

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