. r.avaflow represents an innovative open-source computational tool for routing rapid mass flows, avalanches, or process chains from a defined release area down an arbitrary topography to a deposition area. In contrast to most existing computational tools, r.avaflow (i) employs a two-phase, interacting solid and fluid mixture model (Pudasaini, 2012); (ii) is suitable for modelling more or less complex process chains and interactions; (iii) explicitly considers both entrainment and stopping with deposition, i.e. the change of the basal topography; (iv) allows for the definition of multiple release masses, and/or hydrographs; and (v) serves with built-in functionalities for validation, parameter optimization, and sensitivity analysis. r.avaflow is freely available as a raster module of the GRASS GIS software, employing the programming languages Python and C along with the statistical software R. We exemplify the functionalities of r.avaflow by means of two sets of computational experiments: (1) generic process chains consisting in bulk mass and hydrograph release into a reservoir with entrainment of the dam and impact downstream; (2) the prehistoric Acheron rock avalanche, New Zealand. The simulation results are generally plausible for (1) and, after the optimization of two key parameters, reasonably in line with the corresponding observations for (2). However, we identify some potential to enhance the analytic and numerical concepts. Further, thorough parameter studies will be necessary in order to make r.avaflow fit for reliable forward simulations of possible future mass flow events.

/pdf/r-avaflow-v1-an-advanced-open-source-computational-framework-4tvee1a825.pdf

r.avaflow v1, an advanced open-source computational framework for the propagation and interaction of two-phase mass flows

Earth-surface mass flows such as debris flows, rock avalanches, and dam-break floods can grow greatly in size and destructive potential by entraining bed material they encounter. Increasing use of depth-integrated mass and momentum conservation equations to model these erosive flows motivates a review of the underlying theory. Our review indicates that many existing models apply depth-integrated conservation principles incorrectly, leading to spurious inferences about the role of mass and momentum exchanges at flow-bed boundaries. Model discrepancies can be rectified by analyzing conservation of mass and momentum in a two-layer system consisting of amoving upper layer and static lower layer. Our analysis shows that erosion or deposition rates at the interface between layers must, in general, satisfy three jump conditions. These conditions impose constraints on valid erosion formulas, and they help determine the correct forms of depth-integrated conservation equations. Two of the three jump conditions are closely analogous to Rankine-Hugoniot conditions that describe the behavior of shocks in compressible gasses, and the third jump condition describes shear traction discontinuities that necessarily exist across eroding boundaries. Grain-fluid mixtures commonly behave as compressible materials as they undergo entrainment, because changes in bulk density occur as the mixtures mobilize and merge with an overriding flow. If no bulk density change occurs, then only the shear traction jump condition applies. Even for this special case, however, accurate formulation of depth-integrated momentum equations requires a clear distinction between boundary shear tractions that exist in the presence or absence of bed erosion.

Entrainment of bed material by Earth‐surface mass flows: Review and reformulation of depth‐integrated theory

[1] Analyses of mass and momentum exchange between a debris flow or avalanche and an underlying sediment layer aid interpretations and predictions of bed-sediment entrainment rates. A preliminary analysis assesses the behavior of a Coulomb slide block that entrains bed material as it descends a uniform slope. The analysis demonstrates that the block's momentum can grow unstably, even in the presence of limited entrainment efficiency. A more-detailed, depth-integrated continuum analysis of interacting, deformable bodies identifies mechanical controls on entrainment efficiency, and shows that entrainment rates satisfy a jump condition that involves shear-traction and velocity discontinuities at the flow-bed boundary. Explicit predictions of the entrainment rateEresult from making reasonable assumptions about flow velocity profiles and boundary shear tractions. For Coulomb-friction tractions, predicted entrainment rates are sensitive to pore fluid pressures that develop in bed sediment as it is overridden. In the simplest scenario the bed sediment liquefies completely, and the entrainment-rate equation reduces toE = 2μ1gh1 cos θ(1 − λ1)/ v¯1, where θ is the slope angle, μ1 is the flow's Coulomb friction coefficient, h1 is its thickness, λ1 is its degree of liquefaction, and v¯1is its depth-averaged velocity. For values ofλ1ranging from 0.5 to 0.8, this equation predicts entrainment rates consistent with rates of 0.05 to 0.1 m/s measured in large-scale debris-flow experiments in which wet sediment beds liquefied almost completely. The propensity for bed liquefaction depends on several factors, including sediment porosity, permeability, and thickness, and rates of compression and shear deformation that occur when beds are overridden.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JF002189

Elementary theory of bed-sediment entrainment by debris flows and avalanches

https://cyberleninka.org/article/n/141011.pdf

A review of source term estimation methods for atmospheric dispersion events using static or mobile sensors

This paper describes a coupled, distributed, hydrological-geotechnical model, GEOtop-FS, which simulates the probability of occurrence of shallow landslides and debris flows. We use a hydrological distributed model, GEOtop, which, models latent and sensible heat fluxes and surface runoff, and computes soil moisture in 3-D by solving Richards'equation numerically, together with an infinite-slope geotechnical model, GEOtop-FS. The combined model allows both the hydraulic and geotechnical properties of soil to be considered and realistically modelled. In particular, the model has been conceived to make direct use of field surveys, geotechnical characteristics and soil moisture measurements. In the model the depth of available sediments is also used to characterize the hydraulic properties of the area examined. To account for the uncertainty related to the natural variability in the factors influencing the stability of natural slopes, the safety factor is computed with a probabilistic approach. In order to determine the likelihood of slope failures, soil parameters are assigned distributions instead of single deterministic values. The analysis presented was carried out for an alpine watershed, located in the Friuli region, Italy, for which some geological and geotechnical data were available. In the past, this watershed experienced landslides and debris flows during intense storms following long and moderate intensity rainfall events. The distributed coupled GEOtop-FS model was calibrated by reproducing some of these events and validated in order to map future failure probabilities.

Modelling the probability of occurrence of shallow landslides and channelized debris flows using GEOtop‐FS

[2] Determining the risk associated with hazards involves many factors; examining strategies for mitigation is, likewise, a complicated problem. It is increasingly common to turn to models and computer simulation to assist in the risk assessment and mitigation process. In studying hazardous natural flows with models and simulations, we seek answers to questions such as ‘‘Is a particular village likely to be affected by flows in a given time frame? Should we construct a road along this valley or along a different one?’’ The answer to such a question in full generality requires an accounting of the uncertainties in the frequency and magnitude of likely flow events. Then, given the occurrence of a flow of some specified size, we also require measurable confidence in the prediction of the flow physics by a computational model. However, for most models such predictions of flow physics are difficult to obtain in absolute terms due to the uncertainties associated with assumed values of model inputs, parameters, and, oftentimes, with the model itself (details of the parametric and model

Input Uncertainty Propagation Methods and Hazard Mapping of Geophysical Mass Flows

We present a framework for modeling a dry geophysical mass of
granular material -- a debris or volcanic avalanche or landslide
-- flowing over an erodible surface. We also describe a computing
environment that incorporates topographical data into a parallel,
adaptive mesh computational algorithm that solves the model
equations.

A model of granular flows over an erodible surface

http://www.math.buffalo.edu/~pitman/papers/dgpaper.pdf

Parallel adaptive discontinuous Galerkin approximation for thin layer avalanche modeling

This paper describes the development of highly accurate adaptive discontinuous Galerkin schemes for the solution of the equations arising from a thin layer type model of debris flows. Such flows have wide applicability in the analysis of avalanches induced by many natural calamities, e.g. volcanoes, earthquakes, etc. These schemes are coupled with special parallel solution methodologies to produce a simulation tool capable of very high-order numerical accuracy. The methodology successfully replicates cold rock avalanches at Mount Rainier, Washington and hot volcanic particulate flows at Colima Volcano, Mexico.

Validation of TITAN2D flow model code for pyroclastic flows and debris avalanches at Soufrière Hills Volcano, Montserrat, BWI

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Input Uncertainty Propagation Methods and Hazard Mapping of Geophysical Mass Flows

A model of granular flows over an erodible surface

Parallel adaptive discontinuous Galerkin approximation for thin layer avalanche modeling

Parallel adaptive discontinuous Galerkin approximation for thin layer avalanche modeling

Validation of TITAN2D flow model code for pyroclastic flows and debris avalanches at Soufrière Hills Volcano, Montserrat, BWI