Field Measurements of Forces in Debris Flows at the Illgraben: Implications for Channel-Bed Erosion

Abstract Shortly before the beginning of the 2017–2018 winter rainy season, one of the largest fires in California (USA) history (Thomas fire) substantially increased the susceptibility of steep slopes in Santa Barbara and Ventura Counties to debris flows. On 9 January 2018, before the fire was fully contained, an intense burst of rain fell on the portion of the burn area above Montecito, California. The rainfall and associated runoff triggered a series of debris flows that mobilized ∼680,000 m3 of sediment (including boulders >6 m in diameter) at velocities up to 4 m/s down coalescing urbanized alluvial fans. The resulting destruction (including 23 fatalities, at least 167 injuries, and 408 damaged homes) underscores the need for improved understanding of debris-flow runout in the built environment, and the need for a comprehensive framework to assess the potential loss from debris flows following wildfire. We present observations of the inundation, debris-flow dynamics, and damage from the event. The data include field measurements of flow depth and deposit characteristics made within the first 12 days after the event (before ephemeral features of the deposits were lost to recovery operations); an inventory of building damage; estimates of flow velocity; information on flow timing; soil-hydrologic properties; and post-event imagery and lidar. Together, these data provide rare spatial and dynamic constraints for testing debris-flow runout models, which are needed for advancing post-fire debris-flow hazard assessments. Our analysis also outlines a framework for translating the results of these models into estimates of economic loss based on an adaptation of the U.S. Federal Emergency Management Agency’s Hazus model for tsunamis.

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Predicting deposition of debris flows in mountain channels

Canadian Geotechnical Journal ◽

10.1139/t90-057 ◽

1990 ◽

Vol 27 (4) ◽

pp. 409-417 ◽

Cited By ~ 137

Author(s):

Lee E. Benda ◽

Terrance W. Cundy

Keyword(s):

Pacific Northwest ◽

Debris Flows ◽

Field Measurements ◽

Coast Range ◽

Oregon Coast Range ◽

Oregon Coast ◽

Aerial Photos ◽

The Pacific ◽

Channel Slope ◽

Junction Angle

An empirical model for predicting deposition of coarse-textured debris flows in confined mountain channels is developed based on field measurements of 14 debris flows in the Pacific Northwest, U.S.A. The model uses two criteria for deposition: channel slope (less than 3.5°) and tributary junction angle (greater than 70°). The model is tested by predicting travel distances of 15 debris flows in the Oregon Coast Range and six debris flows in the Washington Cascades, U.S.A. The model is further tested on 44 debris flows in two lithological types in the Oregon Coast Range using aerial photos and topographic maps; on these flows only the approximate travel distance is known. The model can be used by resource professionals to identify the potential for impacts from debris flows. Key words: debris flow, deposition, travel, erosion.

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A novel method for measuring the timing of bed erosion during debris flows and floods

Water Resources Research ◽

10.1029/2009wr007993 ◽

2010 ◽

Vol 46 (2) ◽

Cited By ~ 27

Author(s):

Catherine Berger ◽

Brian W. McArdell ◽

Bruno Fritschi ◽

Fritz Schlunegger

Keyword(s):

Debris Flows ◽

Bed Erosion ◽

Novel Method

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Surface velocity computation of debris flows by vector field measurements

Physics and Chemistry of the Earth Part B Hydrology Oceans and Atmosphere ◽

10.1016/s1464-1909(00)00095-2 ◽

2000 ◽

Vol 25 (9) ◽

pp. 741-744 ◽

Cited By ~ 4

Author(s):

H. Inaba ◽

Y. Itakura ◽

M. Kasahara

Keyword(s):

Vector Field ◽

Debris Flows ◽

Field Measurements ◽

Surface Velocity

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The importance of erosion for debris flow runout modelling from applications to the Swiss Alps

Natural Hazards and Earth System Sciences Discussions ◽

10.5194/nhessd-3-2379-2015 ◽

2015 ◽

Vol 3 (4) ◽

pp. 2379-2417 ◽

Cited By ~ 3

Author(s):

F. Frank ◽

B. W. McArdell ◽

C. Huggel ◽

A. Vieli

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Field Data ◽

Hazard Analysis ◽

Maximum Shear Stress ◽

Swiss Alps ◽

Erosion Model ◽

Practical Applications ◽

Bed Erosion ◽

The Relationship

Abstract. This study describes an investigation of channel-bed erosion of sediment by debris flows. An erosion model, developed using field data from debris flows at the Illgraben catchment, Switzerland, was incorporated into the existing RAMMS debris-flow model, which solves the 2-D shallow-water equations for granular flows. In the erosion model, the relationship between maximum shear stress and measured erosion is used to determine the maximum potential erosion depth. Additionally, the maximum rate of erosion, measured at the same field site, is used to constrain the erosion rate. The model predicts plausible erosion values in comparison with field data from highly erosive debris flow events at the Spreitgraben torrent channel, Switzerland in 2010, without any adjustment to the coefficients in the erosion model. We find that by including channel erosion in runout models a more realistic flow pattern is produced than in simulations where entrainment is not included. In detail, simulations without channel bed erosion show more lateral outflow from the channel where it has not been observed in the field. Therefore the erosion model may be especially useful for practical applications such as hazard analysis and mapping, as well as scientific case studies of erosive debris flows.

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Analysis of the load exerted by debris flows on filter barriers: Comparison between numerical results and field measurements

Computers and Geotechnics ◽

10.1016/j.compgeo.2019.103311 ◽

2020 ◽

Vol 118 ◽

pp. 103311 ◽

Cited By ~ 3

Author(s):

Alessandro Leonardi ◽

Marina Pirulli

Keyword(s):

Debris Flows ◽

Field Measurements ◽

Numerical Results

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Debris flows: some physical characteristics and behaviour

Canadian Geotechnical Journal ◽

10.1139/t93-007 ◽

1993 ◽

Vol 30 (1) ◽

pp. 71-81 ◽

Cited By ~ 52

Author(s):

R. J. Fannin ◽

T. P. Rollerson

Keyword(s):

Debris Flows ◽

Slope Angle ◽

Field Measurements ◽

Cohesive Soil ◽

Study Data ◽

Physical Characteristics ◽

Infinite Slope ◽

Queen Charlotte Islands ◽

Morphological Criteria ◽

Field Drainage

Field observations on 449 debris flows in the Queen Charlotte Islands, British Columbia, are summarized. Movement of debris is classified according to seven characteristic types designated for the purposes of the study. Data on the physical characteristics of the events are presented. An analysis of the data is made with reference to event initiation, yield, and deposition using both mechanistic and morphological criteria. For those events which initiate on an open slope, the infinite slope model is used to establish a relationship between field drainage class and slope angle, for assumed frictional and cohesive soil strength parameters. The field drainage classes are directly related to the postulated location of the groundwater surface within the depth of the rupture plane. Deposition of channelized events is found to be influenced by the ratio of channel width to channel gradient, with the onset of deposition expected when the ratio exceeds unity. Five classes of depositional area are proposed. The magnitude of debris material deposited by an event is described by a channel debris yield rate which shows considerable variation with each event type. The conclusions of this study are based on postevent field measurements of deposited and eroded debris material. A limitation of the study arises from the difficulty of accurately describing an event some years after it has taken place. Key words : slope stability, debris flow, infinite slope analysis, debris yield.

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

Natural Hazards and Earth System Science ◽

10.5194/nhess-17-345-2017 ◽

2017 ◽

Vol 17 (3) ◽

pp. 345-356 ◽

Cited By ~ 13

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.

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Field Measurements of Debris Flows in the Mizunashi and Nakao Rivers on Mt Unzen-Hugen Dake.

Doboku Gakkai Ronbunshu ◽

10.2208/jscej.1999.635_49 ◽

1999 ◽

pp. 49-65 ◽

Cited By ~ 1

Author(s):

Muneo HIRANO ◽

Haruyuki HASHIMOTO ◽

Michinari KOUNO ◽

Kunihiko ONDA ◽

Kichan PARK

Keyword(s):

Debris Flows ◽

Field Measurements

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Numerical Simulation of Debris Flows

Volume 6: Materials Technology; C.C. Mei Symposium on Wave Mechanics and Hydrodynamics; Offshore Measurement and Data Interpretation ◽

10.1115/omae2009-79197 ◽

2009 ◽

Cited By ~ 1

Author(s):

Ko-Fei Liu ◽

Ming-Chun Huang

Keyword(s):

Debris Flows ◽

Plug Flow ◽

Field Measurements ◽

Bottom Layer ◽

Field Application ◽

Constitutive Law ◽

Central Difference ◽

Order Scheme ◽

Complicated Geometry ◽

Numerical Program

A numerical program developed for field application is presented in this paper. We use the generalized Julien and Lan (1991) rheological model to simulate debris flows. Due to the derivative discontinuous nature of the constitutive law, flow is separated into plug region and bottom region (with stress greater than yield stress). The program solves the plug flow layer solution first and then corrects the solution with the bottom layer approximation. Numerical scheme with upwind method and central difference in space and Adam-Bashforth 3rd order scheme in time is used for both layers. The scheme is tested against analytical solutions and laboratory experiments with very good results. Application to a field case with more complicated geometry, also achieves good agreement with error less than 5% compared with field measurements. Final example demonstrates how this numerical program is used in a preliminary design.

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