scholarly journals Evaluation of Debris Flows for Flood Plain Estimation in a Small Ungauged Tropical Watershed for Hurricane Otto

Hydrology ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 122
Author(s):  
Sebastián Fallas Salazar ◽  
Alejandra M. Rojas González
Keyword(s):  
Debris Flows ◽  
Flood Plain ◽  
Rain Gauge ◽  
Economic Losses ◽  
Clean Water ◽  
Newtonian Flows ◽  
Bias Factor ◽  
Input Source ◽  
Debris Flood ◽  
Tropical Watershed

The variability of climate, increase in population, and lack of territorial plans in Costa Rica have caused intense disasters with human and economic losses. In 2016, Hurricane Otto hit the country’s northern area, leaving substantial damages, including landslides, debris flows, and flooding. The present study evaluated different scenarios to estimate flooded areas for Newtonian (clean water), and non-Newtonian flows with volumetric sediment concentrations (Cv) of 0.3, 0.45, 0.55, and 0.65 using Hydro-Estimator (HE), rain gauge station, and the 100-year return period event. HEC–HMS modeled the rainfall products, and FLO-2D modeled the hydrographs and Cv combinations. The simulation results were evaluated with continuous statistics, contingency table, Nash Sutcliffe Efficiency, measure of fit (F), and mean absolute differences (E) in the floodplains. Flow depths, velocities, and hazard intensities were obtained in the floodplain. The debris flood was validated with field data and classified with a Cv of 0.45, presenting lower MAE and RMSE. Results indicated no significant differences in flood depths between hydrological scenarios with clean-water simulations with a difference of 8.38% in the peak flow. The flood plain generated with HE rainfall and clear-water condition presented similar results compared to the rain gauge input source. Additionally, hydraulic results with HE and Cv of 0.45 presented E and F values similar to the simulation of Cv of 0.3, demonstrating that the HE bias did not influence the determination of the floodplain depth and extent. A mean bias factor can be applied to a sub-daily temporal resolution to enhance HE rain rate quantifications and floodplain determination.

scholarly journals Comparison of length and dynamics of wood pieces in streams covered with coniferous and broadleaf forests mapped using orthophotos acquired by an unmanned aerial vehicle

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Haruka Tsunetaka ◽  
Slim Mtibaa ◽  
Shiho Asano ◽  
Takashi Okamoto ◽  
Ushio Kurokawa
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Debris Flows ◽  
Rain Gauge ◽  
Japan Meteorological Agency ◽  
Landslide Occurrence ◽  
Direct Measurements ◽  
Wood Piece ◽  
Aerial Vehicle ◽  
Main Components ◽  
Landslides And Debris Flows

AbstractAs wood pieces supplied by landslides and debris flows are one of the main components of ecological and geomorphic systems, the importance of quantifying the dimensions of the wood pieces is evident. However, the low accessibility of disturbed channels after debris flows generally impedes accurate and quick wood-piece investigations. Thus, remote-sensing measurements for wood pieces are necessitated. Focusing on sub-watersheds in coniferous and broadleaf forests in Japan (the CF and BF sites, respectively), we measured the lengths of wood pieces supplied by landslides (> 0.2 m length and > 0.03 m diameter) from orthophotos acquired using a small unmanned aerial vehicle (UAV). The measurement accuracy was analyzed by comparing the lengths derived from the UAV method with direct measurements. The landslides at the CF and BF sites were triggered by extremely heavy rainfalls in 2017 and 2018, respectively. UAV flights were operated during February and September 2019 at the CF site and during November 2018 and December 2019 at the BF site. Direct measurements of wood pieces were carried out on the date of the respective second flight date in each site. When both ends of a wood piece are satisfactorily extracted from an orthophoto acquired by the UAV, the wood-piece lengths at the CF site can be measured with an accuracy of approximately ±0.5 m. At the BF site, most of the extracted lengths were shorter than the directly measured lengths, probably because the complex structures of the root wad and tree crown reduced the visibility. Most wood pieces were discharged from landslide scars at the BF site, but at the CF site, approximately 750 wood pieces remained in the landslide scars approximately 19 months after the landslide occurrence. The number of wood pieces in the landslide scars of the CF site increased with increasing landslide area, suggesting that some wood pieces can be left even if large landslides occur. The lengths and locations of the entrapped wood pieces at both sites were not significantly changed between the two UAV flight dates. However, during this period, the rainfall intensities around the CF site measured by the closest rain-gauge of the Japan Meteorological Agency reached their second highest values from 1976 to 2019, which exceeded the 30-year return period. This suggests that most of the entrapped wood pieces rarely migrated even under intense rainfall.

scholarly journals Empirical atmospheric thresholds for debris flows and flash floods in the southern French Alps

2014 ◽  
Vol 14 (6) ◽  
pp. 1517-1530 ◽  
Author(s):  
T. Turkington ◽  
J. Ettema ◽  
C. J. van Westen ◽  
K. Breinl
Keyword(s):  
Debris Flows ◽  
Warning System ◽  
Flash Floods ◽  
Rain Gauge ◽  
Reanalysis Data ◽  
Specific Humidity ◽  
Atmospheric Conditions ◽  
Convective Rainfall ◽  
French Alps ◽  
Mountainous Regions

Abstract. Debris flows and flash floods are often preceded by intense, convective rainfall. The establishment of reliable rainfall thresholds is an important component for quantitative hazard and risk assessment, and for the development of an early warning system. Traditional empirical thresholds based on peak intensity, duration and antecedent rainfall can be difficult to verify due to the localized character of the rainfall and the absence of weather radar or sufficiently dense rain gauge networks in mountainous regions. However, convective rainfall can be strongly linked to regional atmospheric patterns and profiles. There is potential to employ this in empirical threshold analysis. This work develops a methodology to determine robust thresholds for flash floods and debris flows utilizing regional atmospheric conditions derived from ECMWF ERA-Interim reanalysis data, comparing the results with rain-gauge-derived thresholds. The method includes selecting the appropriate atmospheric indicators, categorizing the potential thresholds, determining and testing the thresholds. The method is tested in the Ubaye Valley in the southern French Alps (548 km2), which is known to have localized convection triggered debris flows and flash floods. This paper shows that instability of the atmosphere and specific humidity at 700 hPa are the most important atmospheric indicators for debris flows and flash floods in the study area. Furthermore, this paper demonstrates that atmospheric reanalysis data are an important asset, and could replace rainfall measurements in empirical exceedance thresholds for debris flows and flash floods.

scholarly journals Low-density debris flows and floods modeling in the Susuya river basin

2020 ◽  
Vol 163 ◽  
pp. 02006
Author(s):  
Viktoriia Kurovskaia ◽  
Tatyana Vinogradova ◽  
Anastasiia Vasiakina
Keyword(s):  
Debris Flows ◽  
Water Movement ◽  
Residential Buildings ◽  
Flood Plain ◽  
Flow Density ◽  
Low Density ◽  
Initial Information ◽  
Construction Design ◽  
Significant Area ◽  
Optimal Values

Significant area of Yuzhno-Sakhalinsk city within the river Susuya flood plain, a terrace above it and its tributaries are located in flood prone zone. The aim of this research was to estimate maximum characteristics of flash floods and low-density debris flows for the Susuya river and its tributaries, the Rogatka and Vladimirovka rivers. A one-dimensional model of unsteady water movement based on Saint-Venan equations was used. The modeling of river maximum characteristics include following tasks: 1) collect and analyze the data of past dangerous events, 2) process the initial information for the model, 3) simulate discharges of 0.1-10% exceeding probabilities with a change in the hydraulic-morphometric characteristics of the objects. The model does not take into account flow density, therefore numerical experiments were conducted with the increasing coefficient of roughness to identify optimal values of the parameter. The results can be further used in the construction design of residential buildings and infrastructure in Yuzhno-Sakhalinsk.

scholarly journals Prediction of Precipitation in the Western Mountainous Regions of China Using a Statistical Model

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Yijia Hu ◽  
Yuan Sun ◽  
Yao Ha ◽  
Yimin Zhu ◽  
Zhixian Luo
Keyword(s):  
Statistical Model ◽  
Debris Flows ◽  
Summer Precipitation ◽  
Heavy Rain ◽  
Precipitation Anomaly ◽  
Economic Losses ◽  
Sample Return ◽  
Mountainous Regions ◽  
Landslides And Debris Flows ◽  
Cross Test

During the summer in the western mountainous regions of China (WMR), the disasters such as mountain floods, landslides, and debris flows caused by heavy rain occur frequently, which often result in huge economic losses and many casualties. Therefore, it is of great significance to predict the precipitation accurately in these regions. In this paper, a statistical model is established to predict the precipitation in the WMR using the linear regression statistical method, in which the summer area-averaged precipitation anomaly in WMR is taken as the predictand and the prewinter Niño3 SST is taken as the predictor. The results of the return cross test for the historical years from 1979 to 2008 and independent sample return test from 2009 to 2018 show that this statistical model has a good performance in predicting the summer precipitation in the WMR, especially in the flood years. It has better skill in the prediction of WMR precipitation than the dynamical model SINTEX-F.

scholarly journals Quantitative Analysis of the Debris Flow Societal Risk to People Inside Buildings at Different Times: A Case Study of Luomo Village, Sichuan, Southwest China

2021 ◽  
Vol 8 ◽  
Author(s):  
Li Wei ◽  
Kaiheng Hu ◽  
Jin Liu
Keyword(s):  
Quantitative Analysis ◽  
Debris Flow ◽  
Debris Flows ◽  
Evaluation Model ◽  
Alluvial Fan ◽  
Economic Losses ◽  
Rural Settlements ◽  
Societal Risk ◽  
Flow Intensity ◽  
The Village

Debris flows, which cause massive economic losses and tragic losses of life every year, represent serious threats to settlements in mountainous areas. Most deaths caused by debris flows in China occur in buildings, and the death toll is strongly dependent on the time people spend indoors. However, the role of time spent indoors in the quantitative analysis of debris flow risk has been studied only scarcely. We chose Luomo village in Sichuan atop a debris flow alluvial fan to study the influence of the temporal variation in the presence of people inside buildings on the societal risk. Two types of days (holidays vs. workdays) and two diurnal periods (daytime vs. nighttime) were considered in our risk evaluation model. A questionnaire survey was conducted for each family in the village, and the probability of the temporal impact of a debris flow on every household was calculated based on the average amount of time each member spent in the house. The debris flow hazard was simulated with FLO-2D to obtain the debris flow intensity and run-out map with return periods of 2, 10, 50, and 100 years. The risk to buildings and societal risk to residents were calculated quantitatively based on the probabilities of debris flow occurrence, the probability of the spatial impact, and the vulnerabilities of buildings and people. The results indicated that societal risk on holidays is always higher than that on weekdays, and societal risk at night is also much higher than that in the daytime, suggesting that the risk to life on holidays and at night is an important consideration. The proposed method permits us to obtain estimates of the probable economic losses and societal risk to people by debris flows in rural settlements and provides a basis for decision-making in the planning of mitigation countermeasures.

Debris-Flow Risk Assessment

2016 ◽  
Author(s):  
Matthias Jakob ◽  
Kris Holm ◽  
Scott McDougall
Keyword(s):  
Risk Assessment ◽  
Debris Flow ◽  
Debris Flows ◽  
Numerical Models ◽  
Risk Tolerance ◽  
Nuclear Industry ◽  
Decision Makers ◽  
Economic Losses ◽  
Landslide Risk ◽  
Frequency Magnitude

Debris flows are one of the most destructive landslide processes worldwide, given their ubiquity in mountainous areas occupied by human settlement or industrial facilities around the world. Given the episodic nature of debris flows, these hazards are often un- or under-recognized. Three fundamental components of debris-flow risk assessments include frequency-magnitude analysis, numerical scenario modeling, and consequence analysis to estimate the severity of damage and loss. Recent advances in frequency-magnitude analysis take advantage of developments in methods to estimate the age of deposits and size of past and potential future events. Notwithstanding, creating reliable frequency-magnitude relationships is often challenged by practical limitations to investigate and statistically analyze past debris-flow events that are often discontinuous, as well as temporally and spatially censored. To estimate flow runout and destructive potential, several models are used worldwide. Simple empirical models have been developed based on statistical geometric correlations, and two-dimensional and three-dimensional numerical models are commercially available. Quantitative risk assessment (QRA) methods for assessing public safety were developed for the nuclear industry in the 1970s and have been applied to landslide risk in Hong Kong starting in 1998. Debris-flow risk analyses estimate the likelihood of a variety of consequences. Quantitative approaches involve prediction of the annual probability of loss of life to individuals or groups and estimates of annualized economic losses. Recent progress in quantitative debris-flow risk analyses include improved methods to characterize elements at risk within a GIS environment and estimates of their vulnerability to impact. Improvements have also been made in how these risks are communicated to decision makers and stakeholders, including graphic display on conventional and interactive online maps. Substantial limitations remain, including the practical impossibility of estimating every direct and indirect risk associated with debris flows and a shortage of data to estimate vulnerabilities to debris-flow impact. Despite these limitations, quantitative debris-flow risk assessment is becoming a preferred framework for decision makers in some jurisdictions, to compare risks to defined risk tolerance thresholds, support decisions to reduce risk, and quantify the residual risk remaining following implementation of risk reduction measures.

Planning for floods after fires: Lessons from the 2018 Montecito Debris Flow (California)

2021 ◽  
Author(s):  
Anna Serra-Llobet ◽  
John Radke ◽  
Mathias Kondolf ◽  
Sarah Lindbergh
Keyword(s):  
Debris Flows ◽  
Planning Process ◽  
Flood Hazard ◽  
Scientific Information ◽  
Economic Losses ◽  
Soil Conditions ◽  
Stream Channels ◽  
Emergency Situations ◽  
Transverse Ranges ◽  
Classic Pattern

<p>On January 9, 2018 a series of debris flows killed 23 people and caused over a $1 billion in economic losses in Montecito, Santa Barbara County. The debris flows followed a classic pattern in mountainous areas of southern California: A large wildfire (the 2017 Thomas Fire) burned the headwaters of streams draining the Transverse Ranges southward to the Pacific, creating hydrophobic soil conditions that prevented infiltration of water, resulting in larger runoff during rains. A cell of intense precipitation over Montecito triggered debris flows, affecting areas along the stream channels. </p><p>The 2018 Montecito debris flows raise compelling questions about the role of scientific information in decision making generally, and specifically how hazardous areas along rivers and streams are mapped, how land use is regulated in these zones, and how best to respond in emergency situations. </p><p>This presentation analyzes the evacuation planning process during the emergency management (making emphasis on the maps used by public officials), the recovery planning strategies that the local government adopted after the event, and the evolution of houses in flood hazard areas since the beginning of the 20<sup>th</sup> century, to highlight the importance of exposure as a key element to reduce risk.</p>

The effects of the storm Gloria in Catalonia: The value of quick-response geological inventories as a tool for risk management

2021 ◽  
Author(s):  
Marta González ◽  
Maria Jesus Micheo ◽  
Jordi Pinyol ◽  
Maria Rosa Carles ◽  
Eulàlia Pi ◽  
...  
Keyword(s):  
Risk Management ◽  
Flow Direction ◽  
Flood Plain ◽  
Mediterranean Coast ◽  
Economic Losses ◽  
Quick Response ◽  
Lower Section ◽  
Slope Movements ◽  
The North ◽  
The Impact

<p>The storm Gloria was an exceptional episode of east storm occurred in the north and east of Spain from Sunday 19<sup>th</sup> to Thursday 23<sup>rd</sup> of January 2020. The impact was especially strong in the Mediterranean coast, causing the overflow of some rivers, abundant slope movements, cuts in the road and rail network, isolation of populations, and huge damage on the coastline.  It was classified as historical, not only because of the multiplicity of phenomena (wind, rain, snow, and waves) that happened simultaneously, but also because of the extension, affecting the entire Catalan territory. In order to have an overview of the effects of the storm in Catalonia, the Institut Cartogràfic i Geològic of Catalonia has carried out a quick response report (González et. Al., 2020), which has consisted of an inventory of the geomorphological impact and its consequences. The work carried out includes the production of post-event orthoimages of the coastal strip and some fluvial courses, a post-event field survey during the days immediately after, and a compilation of the information published in the media between 01/20/2020 and 02/18/2020. Also, a data collection campaign through online forms sent by email has been carried out, which provides more information of the sea gale effects, and validates and complete the preliminary inventory of slope movements. Thus, an inventory of slope movements has been obtained with a total of 352 documented landslides throughout the Catalan territory. In addition, a geomorphological mapping with the changes associated to river dynamics has been carried out, in two of the most affected sectors in NE Catalonia: the lower section of the Tordera river and the lower section of Ter river. This 1: 5 000 scale cartography, identify geomorphological elements from fluvial dynamics (active fluvial channels during the flood, active flood plain, erosion scarps of river banks, flow direction lines) and from coastal dynamics (washoverfans, coastal erosion and new creation stream-mouth bars). Finally, based on the analysis of the data collected, an estimate has been made of the impact that the storm Gloria has had on the territory, and how it has affected the different municipalities, in terms of damages and economic losses. The results of this quick response report allow (i) to have a geomorphological record of the storm extent in the short term, (ii) to provide basic information for the management and recovery of river areas, and (iii) to propose new strategies for geological risk management, among others.</p>

scholarly journals Modeling Shallow Over-Saturated Mixtures on Arbitrary Rigid Topography

2012 ◽  
Vol 28 (3) ◽  
pp. 523-541 ◽  
Author(s):  
I. Luca ◽  
C. Y. Kuo ◽  
K. Hutter ◽  
Y. C. Tai
Keyword(s):  
Free Surface ◽  
Debris Flows ◽  
Lower Layer ◽  
Fluid Layer ◽  
Three Dimensional ◽  
Clean Water ◽  
Basal Surface ◽  
Rheological Models ◽  
Saturated Mixture ◽  
Closure Relations

AbstractIn this paper a system of depth-integrated equations for over-saturated debris flows on three-dimensional topography is derived. The lower layer is a saturated mixture of density preserving solid and fluid constituents, where the pore fluid is in excess, so that an upper fluid layer develops above the mixture layer. At the layer interface fluid mass exchange may exist and for this a parameterization is needed. The emphasis is on the description of the influence on the flow by the curvature of the basal surface, and not on proposing rheological models of the avalanching mass. To this end, a coordinate system fitted to the topography has been used to properly account for the geometry of the basal surface. Thus, the modeling equations have been written in terms of these coordinates, and then simplified by using (1) the depth-averaging technique and (2) ordering approximations in terms of an aspect ratio ϵ which accounts for the scale of the flowing mass. The ensuing equations have been complemented by closure relations, but any other such relations can be postulated. For a shallow two-layer debris with clean water in the upper layer, flowing on a slightly curved surface, the equilibrium free surface is shown to be horizontal.

scholarly journals Characterization of a landslide-triggered debris flow at a rainforest-covered mountain region in Brazil

2021 ◽  
Author(s):  
Victor Carvalho Cabral ◽  
Fábio Augusto Gomes Vieira Reis ◽  
Fernando Mazo D’Affonseca ◽  
Ana Lucía ◽  
Claudia Vanessa dos Santos Corrêa ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Rain Gauge ◽  
Peak Discharge ◽  
Hazard Management ◽  
Magnitude Comparison ◽  
Tropical Regions ◽  
Serra Do Mar ◽  
Total Magnitude

AbstractDebris flows represent great hazard to humans due to their high destructive power. Understanding their hydrogeomorphic dynamics is fundamental in hazard assessment studies, especially in subtropical and tropical regions where debris flows have scarcely been studied when compared to other mass-wasting processes. Thus, this study aims at systematically analyzing the meteorological and geomorphological factors that characterize a landslide-triggered debris flow at the Pedra Branca catchment (Serra do Mar, Brazil), to quantify the debris flow’s magnitude, peak discharge and velocity. A magnitude comparison with empirical equations (Italian Alps, Taiwan, Serra do Mar) is also conducted. The meteorological analysis is based on satellite data and rain gauge measurements, while the geomorphological characterization is based on terrestrial and aerial investigations, with high spatial resolution. The results indicate that it was a large-sized stony debris flow, with a total magnitude of 120,195 m3, a peak discharge of 2146.7 m3 s−1 and a peak velocity of 26.5 m s−1. The debris flow was triggered by a 188-mm rainfall in 3 h (maximum intensity of 128 mm h−1), with an estimated return period of 15 to 20 years, which, combined with the intense accumulation of on-channel debris (ca. 37,000 m3), indicates that new high-magnitude debris flows in the catchment and the region are likely to occur within the next two decades. The knowledge of the potential frequency and magnitude (F–M) can support the creation of F–M relationships for Serra do Mar, a prerequisite for reliable hazard management and monitoring programs.

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