scholarly journals Groundwater fluctuations during a debris flow event in western Norway – triggered by rain and snowmelt

2021 ◽  
Vol 25 (7) ◽  
pp. 4147-4158
Author(s):  
Stein Bondevik ◽  
Asgeir Sorteberg
Keyword(s):  
Debris Flow ◽  
Pore Pressure ◽  
Air Temperature ◽  
Groundwater Level ◽  
Debris Flows ◽  
Trigger Factor ◽  
Rapid Rise ◽  
Groundwater Temperature ◽  
Western Norway ◽  
Short Time

Abstract. Pore pressure is crucial in triggering debris slides and flows. Here we present measurements of groundwater pore pressure and temperature recorded by a piezometer 1.6 m below the surface on a slope susceptible to debris flows in western Norway. One of the largest oscillations in data collected over 4 years coincided with a debris flow event on the slope that occurred during storm Hilde on 15–16 November 2013. More than 100 landslides were registered during the storm. Precipitation totaled about 80–100 mm in 24 h, locally up to 129 mm, and an additional trigger factor for the landslides was a rapid rise in air temperature that caused snowmelt. In the studied slope a fraction of the precipitation first fell as snow. On 15 November, the groundwater level in the hillslope rose by 10 cm/h and reached 44 cm below the surface. At the same time, air temperature rose from 0 ∘C to over 8 ∘C, and the groundwater temperature dropped by 1.5 ∘C. The debris flow probably occurred late in the evening of 15 November, when the groundwater level reached its peak. Measurements of the groundwater in the hillslope in the period 2010–2013 show that the event in 2013 was not exceptional. Storm Dagmar on 25–26 December 2011 caused a similar rise in groundwater level but did not trigger any failures. The data suggest that during heavy rainstorms the slope is in a critical state for a landslide to be triggered for a short time – about 4–5 h.

scholarly journals Groundwater fluctuations during a debris flow event in Western Norway – triggered by rain and snowmelt

2020 ◽  
Author(s):  
Stein Bondevik ◽  
Asgeir Sorteberg
Keyword(s):  
Debris Flow ◽  
Pore Pressure ◽  
Air Temperature ◽  
Groundwater Level ◽  
Trigger Factor ◽  
Groundwater Temperature ◽  
Western Norway ◽  
Storm Rainfall ◽  
Short Time ◽  
Water Pore Pressure

Abstract. Pore pressure is crucial in triggering debris slides and flows. Here we present measurements of ground water pore pressure and temperature recorded by a piezometer 1.6 m below the surface on a slope susceptible to debris flows in Western Norway. One of the largest oscillations in data collected over four years coincided with a debris flow event on the slope that occurred during storm Hilde on 15–16 November 2013. More than 100 landslides were registered during the storm. Rainfall totalled about 80–100 mm in 24 hours, locally up to 129 mm, and an additional trigger factor for the slides was a rapid rise in air temperature that caused snowmelt. On 15 November, the groundwater level in the hillslope rose by 10 cm per hour and reached 44 cm below the surface. At the same time, air temperature rose from 0 °C to over 8 °C, and the groundwater temperature dropped by 1.5 °C. The debris flow probably occurred late in the evening of 15 November, when the groundwater level reached its peak. Measurements of the groundwater in the hillslope in the period 2010–2013 show that the event in 2013 was not exceptional. Storm Dagmar on 25–26 December 2011 caused a similar rise in groundwater level, but did not trigger any failures. The data suggest that during heavy rainstorms the slope is in a critical state for a slide to be triggered for a short time – about 4–5 hours.

Water and Sediment Supply Requirements for Post-Wildfire Debris Flows in the Western United States

2021 ◽  
Vol 27 (1) ◽  
pp. 73-85
Author(s):  
Paul M. Santi ◽  
Blaire Macaulay
Keyword(s):  
Debris Flow ◽  
High Intensity ◽  
Debris Flows ◽  
High Volume ◽  
Sediment Supply ◽  
Time Intervals ◽  
Burned Areas ◽  
Sufficient Intensity ◽  
Water Intensity ◽  
Short Time

ABSTRACT This work explores two hypotheses related to runoff-related post-wildfire debris flows: 1) their initiation is limited by rainstorm intensity rather than cumulative rainfall depths and 2) they are not sediment supply limited. The first hypothesis suggests that it is common to generate more than enough rainfall to account for the volume of water in the debris flow, but to actually produce a debris flow, the water must be delivered with sufficient intensity. This is demonstrated by data from 44 debris flows from eight burned areas in California, Colorado, and Utah. Assuming a debris flow comprises 30 percent water and 70 percent solids, these events were generated during rainstorms that produced an average of 17 times as much water as necessary to develop a debris flow. Even accounting for infiltration, the rainstorms still generated an overabundance of water. Intensity dependence is also shown by numerous cases in which the exact timing of debris flows can be pinpointed and is contemporaneous with high-intensity bursts of rainfall. The hypothesis is also supported by rainfall intensity-duration thresholds where high-volume storms without high-intensity bursts do not generate debris flows. The second hypothesis of sediment-supply independence for the initiation of debris flows is supported by a significant increase in flow volume occurring directly after wildfire, compared to flows in unburned terrain. Also, repeated flows within short time intervals are only possible with an abundance of channel sediment, dry ravel, and bank failure material that can be mobilized. Field observations confirm these sediment sources, even directly after a debris-flow.

Hydrologic conditions leading to debris-flow initiation

1990 ◽  
Vol 27 (6) ◽  
pp. 789-801 ◽  
Author(s):  
K. A. Johnson ◽  
N. Sitar
Keyword(s):  
Debris Flow ◽  
Pore Pressure ◽  
Debris Flows ◽  
Field Investigation ◽  
Hydrologic Response ◽  
Storm Events ◽  
Hillslope Hydrology ◽  
Antecedent Moisture ◽  
Pressure Pulses ◽  
Flow Activity

Mitigation of the hazards posed by debris flows requires an understanding of the mechanisms leading to their initiation. The objectives of this study were to evaluate and document the hydrologic response of a potential debris-flow source area to major rainstorms and to evaluate whether traditional models of hillslope hydrology can account for the observed response. A field site in an area of previous debris-flow activity was instrumented and monitored for two winter seasons. Hydrologic responses for a wide variety of antecedent conditions were recorded, including two storm events that produced well-defined positive pore-pressure pulses at the site and initiated numerous debris flows in the immediate vicinity of the site. The observed hydrologic response was highly dependent on antecedent moisture conditions which can be characterized by soil matric suction measurements. The pressure-head pulses observed had a magnitude of approximately 50 cm of water, were transient, traveled downslope, and exhibited some spatial variability. Traditional models of hillslope hydrology do not fully account for the positive pore-pressure pulses observed high on the hillslope. Key words: debris flow, hillslope hydrology, pore pressure, antecedent moisture, tensiometer, piezometer, field investigation.

scholarly journals Meteorological factors driving glacial till variation and the associated periglacial debris flows in Tianmo Valley, south-eastern Tibetan Plateau

2017 ◽  
Vol 17 (3) ◽  
pp. 345-356 ◽  
Author(s):  
Mingfeng Deng ◽  
Ningsheng Chen ◽  
Mei Liu
Keyword(s):  
Tibetan Plateau ◽  
Debris Flow ◽  
Air Temperature ◽  
Debris Flows ◽  
Large Scale ◽  
Field Measurements ◽  
Glacial Till ◽  
Eastern Tibetan Plateau ◽  
South Eastern ◽  
Air Temperatures

Abstract. Meteorological studies have indicated that high alpine environments are strongly affected by climate warming, and periglacial debris flows are frequent in deglaciated regions. The combination of rainfall and air temperature controls the initiation of periglacial debris flows, and the addition of meltwater due to higher air temperatures enhances the complexity of the triggering mechanism compared to that of storm-induced debris flows. On the south-eastern Tibetan Plateau, where temperate glaciers are widely distributed, numerous periglacial debris flows have occurred over the past 100 years, but none occurred in the Tianmo watershed until 2007. In 2007 and 2010, three large-scale debris flows occurred in the Tianmo Valley. In this study, these three debris flow events were chosen to analyse the impacts of the annual meteorological conditions, including the antecedent air temperature and meteorological triggers. The remote sensing images and field measurements of the adjacent glacier suggested that sharp glacier retreats occurred in the 1 to 2 years preceding the events, which coincided with spikes in the mean annual air temperature. Glacial till changes providing enough active sediment driven by a prolonged increase in the air temperature are a prerequisite of periglacial debris flows. Different factors can trigger periglacial debris flows, and they may include high-intensity rainfall, as in the first and third debris flows, or continuous, long-term increases in air temperature, as in the second debris flow event.

A two-phase dilatant debris flow model based on full scale shear stress and pore pressure measurements

2020 ◽  
Author(s):  
Guillaume Meyrat
Keyword(s):  
Shear Stress ◽  
Debris Flow ◽  
Pore Pressure ◽  
Debris Flows ◽  
Flow Model ◽  
Fluid Composition ◽  
Geophysical Research ◽  
Two Phase ◽  
Non Linear ◽  
Fluid Pore Pressure

<p>Since 2004, observations of shear and normal stresses have been collected at the base of naturally-triggered debris flows at the Illgraben observation station (Wallis, Switzerland) [1].   Because flow height and the normal force are simultaneously measured, and limited observations of basal fluid pore pressure are available, it is possible to investigate how the solid/fluid contents of the flow influence the measured shear stress.  The experimental results have emphasized two debris flow properties: (1) Debris flows are characterized by rocky or boulder-rich front, following by a fluidized tail. Consequently, the mass density varies from large values at the front of the flow to lower values towards the tail. A comparison between different debris flow events, however, likewise reveals that the streamwise change in density can vary dramatically between two different events. (2) The relationship between the measured shear and normal tress is highly non-linear. </p><p>Operating on the assumption that the streamwise change in density (or equivalently change in streamwise composition) is primarily responsible for the observed non-linear stress behavior, we develop a rheological model describing two-phase debris flow motion. The underlying idea behind the model is that the granular content of the flow can dilate, changing the solid/fluid composition of the flow, and thereby alter the bulk flow density. The model allows us to estimate the correct debris flow composition for different classes of debris flow varying from granular to muddy fluid. Based on these results, we are then able to reproduce the measured shear stress data when we simulate the measured events numerically.  The results appear to confirm dilatant-type flow models proposed by Takahashi [2], and later developed in detail by Iverson and George [3]. The model is used to back-calculate recent debris flow events that occurred near Davos Switzerland in 2018/2019.</p><p> </p><p> </p><p> </p><p>REFERENCES</p><ol><li>McArdell, B.W., Bartelt, P. and Kowalski, J. (2007): Field observations of basal forces and fluid pore pressure in a debris flow, Geophysical Research Letters, Vol. 34, No. L07406.</li> </ol><p> </p><ol><li>Takahashi, T. (2007): Debris flows: mechanics, prediction and countermeasures, Taylor and Francis / Balkema, 448pp.</li> </ol><p> </p><ol><li>George, D. L., & Iverson, R. M. (2011). A two-phase debris-flow model that includes coupled evolution of volume fractions, granular dilatancy, and pore-fluid pressure. Italian journal of engineering geology and Environment, 43, 415-424.</li> </ol>

scholarly journals Modelling debris flows down general channels

2005 ◽  
Vol 5 (6) ◽  
pp. 799-819 ◽  
Author(s):  
S. P. Pudasaini ◽  
Y. Wang ◽  
K. Hutter
Keyword(s):  
Debris Flow ◽  
Pressure Distribution ◽  
Pore Pressure ◽  
Debris Flows ◽  
Volume Fraction ◽  
Solid Phase ◽  
Fluid Pressure ◽  
Solid Particles ◽  
Simulation Results ◽  
Model Equations

Abstract. This paper is an extension of the single-phase cohesionless dry granular avalanche model over curved and twisted channels proposed by Pudasaini and Hutter (2003). It is a generalisation of the Savage and Hutter (1989, 1991) equations based on simple channel topography to a two-phase fluid-solid mixture of debris material. Important terms emerging from the correct treatment of the kinematic and dynamic boundary condition, and the variable basal topography are systematically taken into account. For vanishing fluid contribution and torsion-free channel topography our new model equations exactly degenerate to the previous Savage-Hutter model equations while such a degeneration was not possible by the Iverson and Denlinger (2001) model, which, in fact, also aimed to extend the Savage and Hutter model. The model equations of this paper have been rigorously derived; they include the effects of the curvature and torsion of the topography, generally for arbitrarily curved and twisted channels of variable channel width. The equations are put into a standard conservative form of partial differential equations. From these one can easily infer the importance and influence of the pore-fluid-pressure distribution in debris flow dynamics. The solid-phase is modelled by applying a Coulomb dry friction law whereas the fluid phase is assumed to be an incompressible Newtonian fluid. Input parameters of the equations are the internal and bed friction angles of the solid particles, the viscosity and volume fraction of the fluid, the total mixture density and the pore pressure distribution of the fluid at the bed. Given the bed topography and initial geometry and the initial velocity profile of the debris mixture, the model equations are able to describe the dynamics of the depth profile and bed parallel depth-averaged velocity distribution from the initial position to the final deposit. A shock capturing, total variation diminishing numerical scheme is implemented to solve the highly non-linear equations. Simulation results present the combined effects of curvature, torsion and pore pressure on the dynamics of the flow over a general basal topography. These simulation results reveal new physical insight of debris flows over such non-trivial topography. Model equations are applied to laboratory avalanche and debris-flow-flume tests. Very good agreement between the theory and experiments is established.

scholarly journals Learning Case Study of a Shallow-Water Model to Assess an Early-Warning System for Fast Alpine Muddy-Debris-Flow

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 750
Author(s):  
Antonio Pasculli ◽  
Jacopo Cinosi ◽  
Laura Turconi ◽  
Nicola Sciarra
Keyword(s):  
Debris Flow ◽  
Shallow Water ◽  
Early Warning ◽  
Debris Flows ◽  
Early Warning System ◽  
Warning System ◽  
Extreme Weather Events ◽  
Water Model ◽  
Computational Time ◽  
Processing Unit

The current climate change could lead to an intensification of extreme weather events, such as sudden floods and fast flowing debris flows. Accordingly, the availability of an early-warning device system, based on hydrological data and on both accurate and very fast running mathematical-numerical models, would be not only desirable, but also necessary in areas of particular hazard. To this purpose, the 2D Riemann–Godunov shallow-water approach, solved in parallel on a Graphical-Processing-Unit (GPU) (able to drastically reduce calculation time) and implemented with the RiverFlow2D code (version 2017), was selected as a possible tool to be applied within the Alpine contexts. Moreover, it was also necessary to identify a prototype of an actual rainfall monitoring network and an actual debris-flow event, beside the acquisition of an accurate numerical description of the topography. The Marderello’s basin (Alps, Turin, Italy), described by a 5 × 5 m Digital Terrain Model (DTM), equipped with five rain-gauges and one hydrometer and the muddy debris flow event that was monitored on 22 July 2016, were identified as a typical test case, well representative of mountain contexts and the phenomena under study. Several parametric analyses, also including selected infiltration modelling, were carried out in order to individuate the best numerical values fitting the measured data. Different rheological options, such as Coulomb-Turbulent-Yield and others, were tested. Moreover, some useful general suggestions, regarding the improvement of the adopted mathematical modelling, were acquired. The rapidity of the computational time due to the application of the GPU and the comparison between experimental data and numerical results, regarding both the arrival time and the height of the debris wave, clearly show that the selected approaches and methodology can be considered suitable and accurate tools to be included in an early-warning system, based at least on simple acoustic and/or light alarms that can allow rapid evacuation, for fast flowing debris flows.

scholarly journals Numerical Simulation of Non-Homogeneous Viscous Debris-Flows Based on the Smoothed Particle Hydrodynamics (SPH) Method

Water ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 2314 ◽  
Author(s):  
Shu Wang ◽  
Anping Shu ◽  
Matteo Rubinato ◽  
Mengyao Wang ◽  
Jiping Qin
Keyword(s):  
Debris Flow ◽  
Water Content ◽  
Smoothed Particle Hydrodynamics ◽  
Debris Flows ◽  
Sph Method ◽  
Particle Hydrodynamics ◽  
Sph Model ◽  
Smoothed Particle ◽  
The Impact ◽  
Kinetic And Potential Energies

Non-homogeneous viscous debris flows are characterized by high density, impact force and destructiveness, and the complexity of the materials they are made of. This has always made these flows challenging to simulate numerically, and to reproduce experimentally debris flow processes. In this study, the formation-movement process of non-homogeneous debris flow under three different soil configurations was simulated numerically by modifying the formulation of collision, friction, and yield stresses for the existing Smoothed Particle Hydrodynamics (SPH) method. The results obtained by applying this modification to the SPH model clearly demonstrated that the configuration where fine and coarse particles are fully mixed, with no specific layering, produces more fluctuations and instability of the debris flow. The kinetic and potential energies of the fluctuating particles calculated for each scenario have been shown to be affected by the water content by focusing on small local areas. Therefore, this study provides a better understanding and new insights regarding intermittent debris flows, and explains the impact of the water content on their formation and movement processes.

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