scholarly journals Inundation, flow dynamics, and damage in the 9 January 2018 Montecito debris-flow event, California, USA: Opportunities and challenges for post-wildfire risk assessment

Geosphere ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 1140-1163 ◽  
Author(s):  
J.W. Kean ◽  
D.M. Staley ◽  
J.T. Lancaster ◽  
F.K. Rengers ◽  
B.J. Swanson ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Field Measurements ◽  
Economic Loss ◽  
Flow Dynamics ◽  
Dynamic Constraints ◽  
Fire Debris ◽  
Velocity Information ◽  
Intense Burst ◽  
Comprehensive Framework

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.

Observations and Analyses of the 9 January 2018 Debris-Flow Disaster, Santa Barbara County, California

2021 ◽  
Vol 27 (1) ◽  
pp. 3-27
Author(s):  
Jeremy T. Lancaster ◽  
Brian J. Swanson ◽  
Stefani G. Lukashov ◽  
Nina S. Oakley ◽  
Jacob B. Lee ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Extreme Rainfall ◽  
Atmospheric Conditions ◽  
Santa Barbara ◽  
Debris Removal ◽  
Fire Debris ◽  
Santa Barbara County ◽  
Coastal Land

ABSTRACT The post–Thomas Fire debris flows of 9 January 2018 killed 23 people, damaged 558 structures, and caused severe damage to infrastructure in Montecito and Carpinteria, CA. U.S. Highway 101 was closed for 13 days, significantly impacting transportation and commerce in the region. A narrow cold frontal rain band generated extreme rainfall rates within the western burn area, triggering runoff-driven debris flows that inundated 5.6 km2 of coastal land in eastern Santa Barbara County. Collectively, this series of debris flows is comparable in magnitude to the largest documented post-fire debris flows in the state and cost over a billion dollars in debris removal and damages to homes and infrastructure. This study summarizes observations and analyses on the extent and magnitude of inundation areas, debris-flow velocity and volume, and sources of debris-flow material on the south flank of the Santa Ynez Mountains. Additionally, we describe the atmospheric conditions that generated intense rainfall and use precipitation data to compare debris-flow source areas with spatially associated peak 15 minute rainfall amounts. We then couple the physical characterization of the event with a compilation of debris-flow damages to summarize economic impacts.

Towards real-time global assessment of post-fire debris flow hazards with remotely sensed data

2021 ◽  
Author(s):  
Elijah Orland ◽  
Dalia Kirschbaum ◽  
Thomas Stanley
Keyword(s):  
Remote Sensing ◽  
Debris Flow ◽  
Real Time ◽  
Debris Flows ◽  
Remotely Sensed Data ◽  
Model Framework ◽  
Burned Areas ◽  
Early Results ◽  
Fire Debris ◽  
Debris Flow Initiation

<p>As the risk of wildfires increases worldwide, burned steeplands are vulnerable to the secondary hazard of widespread sediment mobilization through debris flows. Following an initial burn, sediment and soil previously restrained by vegetation are no longer consolidated, allowing for easy mobilization into channels and along steep hillslopes through runoff.  Sufficiently powerful rainfall incorporates entrained material into turbulent flows and serves as the primary trigger for debris flow initiation. There is thus an ongoing need to establish the relationship between rainfall and debris flow initiation based on a variety of spatiotemporal preconditions. Previous work establishes regional and local thresholds to constrain the effect of rainfall in recently burned areas, but no empirical or numerical solution has worldwide application. Building from regionally-based efforts in the U.S., this work considers how remote sensing data can be applied to better approximate the post-fire debris flow hazards worldwide using freely available global datasets and software. Our work assesses the utility of remote sensing resources for analyzing burn characteristics, topography, rainfall intensity/duration, and, thus, debris flow initiation. Early results show that global observations are sufficient to delineate background rainfall rates from storms likely to cause debris flows across a variety of burn severity and topographic conditions. However, the dearth of publicly-available post-fire debris flow inventories globally limit the ability to test how the model framework performs within different climatologic and morphologic areas. This work will present preliminary analysis over the Western United States and demonstrate the feasibility of a global, near-real time model to provide situational awareness of potential hazards within recently burned areas worldwide. Future work will also consider how global or regional precipitation forecasts may increase the lead time for improved early warning of these hazards.</p>

Time Since Burning and Rainfall Characteristics Impact Post-Fire Debris-Flow Initiation and Magnitude

2021 ◽  
Vol 27 (1) ◽  
pp. 43-56
Author(s):  
Luke A. McGuire ◽  
Francis K. Rengers ◽  
Nina Oakley ◽  
Jason W. Kean ◽  
Dennis M. Staley ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Debris Flow ◽  
Debris Flows ◽  
Numerical Models ◽  
Ground Cover ◽  
Temporal Changes ◽  
Infiltration Capacity ◽  
Rainfall Characteristics ◽  
San Gabriel Mountains ◽  
Fire Debris

ABSTRACT The extreme heat from wildfire alters soil properties and incinerates vegetation, leading to changes in infiltration capacity, ground cover, soil erodibility, and rainfall interception. These changes promote elevated rates of runoff and sediment transport that increase the likelihood of runoff-generated debris flows. Debris flows are most common in the year immediately following wildfire, but temporal changes in the likelihood and magnitude of debris flows following wildfire are not well constrained. In this study, we combine measurements of soil-hydraulic properties with vegetation survey data and numerical modeling to understand how debris-flow threats are likely to change in steep, burned watersheds during the first 3 years of recovery. We focus on documenting recovery following the 2016 Fish Fire in the San Gabriel Mountains, California, and demonstrate how a numerical model can be used to predict temporal changes in debris-flow properties and initiation thresholds. Numerical modeling suggests that the 15-minute intensity-duration (ID) threshold for debris flows in post-fire year 1 can vary from 15 to 30 mm/hr, depending on how rainfall is temporally distributed within a storm. Simulations further demonstrate that expected debris-flow volumes would be reduced by more than a factor of three following 1 year of recovery and that the 15-minute rainfall ID threshold would increase from 15 to 30 mm/hr to greater than 60 mm/hr by post-fire year 3. These results provide constraints on debris-flow thresholds within the San Gabriel Mountains and highlight the importance of considering local rainfall characteristics when using numerical models to assess debris-flow and flood potential.

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.

Loss Curve Analysis of a Debris Flow: A Case Study on the Daniao Tribe

2013 ◽  
Vol 284-287 ◽  
pp. 1499-1510 ◽  
Author(s):  
Hsin Chi Li ◽  
Ko Fei Liu ◽  
Yu Charn Hsu
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Large Scale ◽  
Financial Burden ◽  
Economic Loss ◽  
Loss Assessment ◽  
Governmental Agencies ◽  
Precautionary Measures ◽  
Exposure Evaluation ◽  
Landslides And Debris Flows

The post-disaster recovery from a debris flow imposes a heavy financial burden on a government; thus, it is necessary for governmental agencies use their limited resources effectively. In this study, we focus on the loss curve assessment, the framework of which includes hazard simulation, exposure evaluation and loss assessment. A numerical program named DEBRIS-2D is used to simulate debris flow hazards of different scale. Then, the latest land usage data and the economic loss model are factored in for exposure and loss assessment. In August 2009, Typhoon Morakot hit Taiwan and horrendous disasters resulted, including large-scale landslides and debris flows. The Daniao tribe in Taitung in eastern Taiwan was hit by one of these debris flows, with a debris-flow volume in excess of 500,000 m3, which was beyond the scope of any recovery plan. We simulate the hazards of the debris flow in different volumes and build the loss curve in relation. Notably, the practice of assessing damage caused by such disasters can help in assessing possible losses before they occur, thus allowing governments to take the necessary precautionary measures.

scholarly journals Risk Identification of Lijiadagou Landslide and Debris Flow Hazards Chain in Yong'an Town, Fengjie County of Chongqing City

2021 ◽  
pp. 1-12
Author(s):  
Q. H. Song ◽  
S. C. Ren ◽  
X. L. LI ◽  
B. L. Chen ◽  
K. Li ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Social Impact ◽  
Source Area ◽  
Economic Loss ◽  
Soil Mass ◽  
Mechanical Analysis ◽  
Field Investigation ◽  
Risk Identification ◽  
Alternate Control

Lijiadagou landslide and debris flow hazards chain in Yong’an Town of Fengjie county is one of the representative geohazards. By using satellite remote sensing technology, field investigation and observation, survey and analysis, mechanical analysis and other technical means, this paper makes qualitative or semi quantitative analysis on the hazard environment, instability probability, vulnerability analysis of elements at risk, risk loss, etc. The risk factors of Lijiadagou landslide and debris flow were identified. The conclusion shows that the unique landform and climate of Lijiadagou lay a foundation for the occurrence of multiple debris flows in the history. Under the alternate control of multiple factors such as the nature of the rock and soil mass, the stratum structure that controls the sliding, the complex geomorphic environment, continuous heavy rainfall and the rise and fall of the water level, there are high risks of landslides and debris flows, threatening about  6,000 residents in the middle and front range of Lijiadagou. The risk economic loss of hazards is about 80 million yuan, and will cause serious social impact. It is urgent to strengthen monitoring and early warning, and at the same time take targeted measures against the landslide source  area to cut off the hazards chain from the source, so as to achieve a multiplier effect with half the effort.

scholarly journals Multiply factors driving continual post-wildfire debris flows with varied rainfall thresholds in the Reneyong Valley, southwestern China

2017 ◽  
Author(s):  
Mingfeng Deng ◽  
Yong Zhang ◽  
Mei Liu ◽  
Yuanhuan Wang ◽  
Wanyin Xie ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Water Repellency ◽  
Drainage Area ◽  
Southwestern China ◽  
Soil Water Repellency ◽  
Rainfall Thresholds ◽  
Rain Gauges ◽  
Ash Layer ◽  
Fire Debris

Abstract. In early June of 2014, wildfire struck the Reneyong Valley in the central Hengduan Mountains of southwestern China. Three days after the wildfire, the first debris flow was triggered in branch No. 3, followed by 2 other debris flows that same year. In August 2015, another debris flow occurred in branches No. 1, No. 2 and No. 3, respectively. Rainfall data from three nearby rain gauges and rainfall totals speculated from debris flow volume suggest the three debris flows in 2014 were generated by isolated convective rainfall. Later, we found that varied rainfall thresholds existed among the branches and that these thresholds might be related to the geological and geomorphic characteristics. The results show that (1) the thresholds of post-fire debris flows tend to increase as time passes; (2) post-fire debris flows in the Reneyong Valley occur with high frequency not only because of the loss of the natural canopy, the occurrences of an ash layer and dry ravels and an increase in soil water repellency but also because of the geology, drainage area, channel gradient and regional arid climate, which may not be affected by wildfire; and (3) the varied rainfall thresholds among the different branches are dependent on the drainage area, as entrainment is controlled by the magnitude of discharge.

scholarly journals Investigation of Post-Fire Debris Flows in Montecito

2018 ◽  
Vol 8 (1) ◽  
pp. 5 ◽  
Author(s):  
Yifei Cui ◽  
Deqiang Cheng ◽  
Dave Chan
Keyword(s):  
Debris Flow ◽  
Water Supply ◽  
Short Duration ◽  
Debris Flows ◽  
Burn Severity ◽  
Occurrence Probability ◽  
Material Sources ◽  
Hypsometric Integral ◽  
Fire Debris ◽  
Flows Over Time

Debris flows in a burned area, post-fire debris flows, are considered as one of the most dangerous geo-hazards due to their high velocity, long run-out distance, and huge destruction to infrastructures. The rainfall threshold to trigger such hazards is often reduced compared with normal debris flow because ashes generated by mountain fires reduce the permeability of the top soil layer, thus increasing surface runoff. At the same time, burnt material and residual debris have very poor geo-mechanical characteristics, e.g., their internal friction angle and cohesion are typically low, and thus an intense rainfall can easily trigger some debris flows. Studying post-fire debris flow enables us to get a deeper understanding of disaster management. In this paper, the debris flow that occurred in Montecito, California, USA, and was affected by the Thomas Fire was used as a case study. Five major watersheds were extracted based on the digital elevation model (DEM). Remote sensing images were used to analyze the wildfire process, the extent of the burned areas, and the burn severity. The hypsometric integral (HI) and short-duration rainfall records of the watersheds around Montecito when the post-fire debris flows occurred were analyzed. Steep terrain, loose and abundant deposits, and sufficient water supply are the important conditions affecting the formation of debris flows. Taking watersheds as the research objects, HI was used to describe the geomorphic and topographic features, open-access rainfall data was used to represent the water supply, and burn severity represented the abundance of material sources. An occurrence probability model of post-fire debris flow based on HI, short-duration heavy rainfall, and burn severity was developed by using a logistic regression model in post-fire areas. By using this model, the occurrence probability of the post-fire debris flow in different watersheds around Montecito was analyzed based on the precipitation with time. Especially, the change characteristics of occurrence probability of debris flows over time based on the model bring a new perspective to observe the obvious change of the danger of post-fire debris flows and it is very useful for early warning of post-fire debris flows.

scholarly journals Evaluation of predictive models for post-fire debris flow occurrence in the western United States

2018 ◽  
Vol 18 (9) ◽  
pp. 2331-2343 ◽  
Author(s):  
Efthymios I. Nikolopoulos ◽  
Elisa Destro ◽  
Md Abul Ehsan Bhuiyan ◽  
Marco Borga ◽  
Emmanouil N. Anagnostou
Keyword(s):  
United States ◽  
Random Forest ◽  
Debris Flow ◽  
Predictive Models ◽  
Debris Flows ◽  
The United States ◽  
Western United States ◽  
Economic Losses ◽  
United States Geological Survey ◽  
Fire Debris

Abstract. Rainfall-induced debris flows in recently burned mountainous areas cause significant economic losses and human casualties. Currently, prediction of post-fire debris flows is widely based on the use of power-law thresholds and logistic regression models. While these procedures have served with certain success in existing operational warning systems, in this study we investigate the potential to improve the efficiency of current predictive models with machine-learning approaches. Specifically, the performance of a predictive model based on the random forest algorithm is compared with current techniques for the prediction of post-fire debris flow occurrence in the western United States. The analysis is based on a database of post-fire debris flows recently published by the United States Geological Survey. Results show that predictive models based on random forest exhibit systematic and considerably improved performance with respect to the other models examined. In addition, the random-forest-based models demonstrated improvement in performance with increasing training sample size, indicating a clear advantage regarding their ability to successfully assimilate new information. Complexity, in terms of variables required for developing the predictive models, is deemed important but the choice of model used is shown to have a greater impact on the overall performance.

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