Debris-flow activity in five adjacent gullies in a limestone mountain range

Abstract Debris-flows are infrequent geomorphic phenomena that shape steep valleys and can repre-sent a severe hazard for human settlements and infrastructure. In this study, a debris-flow event chro-nology has been derived at the regional scale within the Gesäuse National Park (Styria, Austria) using dendrogeomorphic techniques. Sediment sources and deposition areas were mapped by combined field investigation and aerial photography using an Unmanned Aerial Vehicle (UAV). Through the analysis of 384 trees, a total of 47 debris-flows occurring in 19 years between AD 1903 and 2008 were identified in five adjacent gullies. Our results highlight the local variability of debris-flow activi-ty as a result of local thunderstorms and the variable availability of sediment sources.

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Why are some alpine catchments debris-flow active and others not? - the influence of geomorphology on debris-flow initiation

10.5194/egusphere-egu2020-7805 ◽

2020 ◽

Author(s):

Philipp Aigner ◽

Leonard Sklar ◽

Markus Hrachowitz ◽

Roland Kaitna

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Regional Scale ◽

Alpine Regions ◽

Order Of Magnitude ◽

Elevation Changes ◽

Alpine Catchments ◽

Flow Activity ◽

The Impact ◽

Debris Flow Susceptibility

Processes like flash floods or debris flows, which typically occur in small headwater catchments, represent a substantial natural hazard in alpine regions. Due to the entrainment of sediment, the discharge of debris flows can be up to an order of magnitude larger compared to 100-year fluvial flood events in the same channel, which poses a great threat to affected communities. Besides the triggering rainfall, the initiation of debris flows depends on the watershed&#8217;s hydrological and geomorphological susceptibility, which makes it hard to predict and understand where and when debris flows occur.In this study we aim to quantify the influence of geomorphologic characteristics and long-term sediment dynamics on debris flow activity in the Austrian Alps. Based on a database of debris-flow events within the last 60+ years, a geomorphological assessment of active and non-active sub-catchments in different study regions is carried out. In a first step, we derive geomorphological characteristics, such as terrain roughness, Melton number as well as weathering potential of geological units found within the watersheds. Based on the findings of the terrain shape analysis, a set of representative watersheds will be selected for systematic monitoring of surface elevation changes over the project period of three years. This will be achieved by comparing digital surface models based on photogrammetric UAV surveys and monitoring of channel reaches with cameras.In order to project these findings onto a larger regional scale, the derived terrain parameters will be used to integrate and extend a previously designed hydro-meteorological debris-flow susceptibility model (Prenner et al., 2018) with a sediment-disposition-model. This will form the basis for an advanced debris flow forecasting tool and help to better assess the impact of climate change on the magnitude and frequency of future debris flows.&#160;<div>References:</div><div>Prenner, D., Kaitna, R., Mostbauer, K., & Hrachowitz, M. ( 2018). The value of using multiple hydrometeorological variables to predict temporal debris flow susceptibility in an Alpine environment. Water Resources Research, 54, 6822&#8211; 6843. </div>&#160;

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Hydrologic conditions leading to debris-flow initiation

Canadian Geotechnical Journal ◽

10.1139/t90-092 ◽

1990 ◽

Vol 27 (6) ◽

pp. 789-801 ◽

Cited By ~ 164

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.

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Forecasting and Seismic Detection of Proglacial Debris Flows at Mount Rainier National Park, Washington, USA

Environmental and Engineering Geoscience ◽

10.2113/eeg-d-20-00014 ◽

2021 ◽

Vol 27 (1) ◽

pp. 57-72

Author(s):

Scott R. Beason ◽

Nicholas T. Legg ◽

Taylor R. Kenyon ◽

Robert P. Jost

Keyword(s):

Debris Flow ◽

Real Time ◽

Debris Flows ◽

National Park ◽

Weather Conditions ◽

Outburst Floods ◽

Mount Rainier ◽

Mount Rainier National Park ◽

High Precipitation ◽

Flow Activity

ABSTRACT The glaciated Mount Rainier volcano in southwestern Washington State (United States) has a rich history of outburst floods and debris flows that have adversely impacted infrastructure at Mount Rainier National Park in the 20th and 21st centuries. Retreating glaciers leave behind vast amounts of unconsolidated till that is easily mobilized during high-precipitation-intensity storms in the fall months, and during outburst floods during warm summer months. Over 60 debris flows and outburst floods have been documented between 1926 and 2019 at Mount Rainier. Debris-flow activity has led to the closure of campgrounds and visitor destinations, which has limited visitor access to large swaths of the park. This paper documents efforts to characterize and seismically monitor debris flows, map hazards, and develop forecasting approaches for wet and dry weather debris flows. Using the day-of and historic antecedent weather conditions on past debris-flow days, we developed a debris-flow hazard model to help predict those days with a higher relative hazard for debris-flow activity park-wide based on prevailing and forecasted weather conditions. Debris flows are detected in near-real-time using the U.S. Geological Survey Real-time Seismic Amplitude Measurement (RSAM) tool. If an event is detected, we can then provide evacuation alerts to employees and visitors working and recreating in the areas downstream. Our goal is to accurately forecast the debris-flow hazards up to 7 days ahead of time and then use RSAM to detect debris flows within minutes of their genesis.

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Debris-flow activity in abandoned channels of the Manival torrent reconstructed with LiDAR and tree-ring data

Natural Hazards and Earth System Science ◽

10.5194/nhess-11-1247-2011 ◽

2011 ◽

Vol 11 (5) ◽

pp. 1247-1257 ◽

Cited By ~ 22

Author(s):

J. Lopez Saez ◽

C. Corona ◽

M. Stoffel ◽

A. Gotteland ◽

F. Berger ◽

...

Keyword(s):

Debris Flow ◽

Tree Ring ◽

Debris Flows ◽

Temporal Distribution ◽

Alluvial Fan ◽

Tree Ring Data ◽

Pine Trees ◽

Spatio Temporal ◽

Flow Activity ◽

Abandoned Channels

Abstract. Hydrogeomorphic processes are a major threat in many parts of the Alps, where they periodically damage infrastructure, disrupt transportation corridors or even cause loss of life. Nonetheless, past torrential activity and the analysis of areas affected during particular events remain often imprecise. It was therefore the purpose of this study to reconstruct spatio-temporal patterns of past debris-flow activity in abandoned channels on the forested cone of the Manival torrent (Massif de la Chartreuse, French Prealps). A Light Detecting and Ranging (LiDAR) generated Digital Elevation Model (DEM) was used to identify five abandoned channels and related depositional forms (lobes, lateral levees) in the proximal alluvial fan of the torrent. A total of 156 Scots pine trees (Pinus sylvestris L.) with clear signs of debris flow events was analyzed and growth disturbances (GD) assessed, such as callus tissue, the onset of compression wood or abrupt growth suppression. In total, 375 GD were identified in the tree-ring samples, pointing to 13 debris-flow events for the period 1931–2008. While debris flows appear to be very common at Manival, they have only rarely propagated outside the main channel over the past 80 years. Furthermore, analysis of the spatial distribution of disturbed trees contributed to the identification of four patterns of debris-flow routing and led to the determination of three preferential breakout locations. Finally, the results of this study demonstrate that the temporal distribution of debris flows did not exhibit significant variations since the beginning of the 20th century.

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The temporally varying roles of rainfall, snowmelt and soil moisture for debris flow initiation in a snow-dominated system

Hydrology and Earth System Sciences ◽

10.5194/hess-22-3493-2018 ◽

2018 ◽

Vol 22 (6) ◽

pp. 3493-3513 ◽

Cited By ~ 10

Author(s):

Karin Mostbauer ◽

Roland Kaitna ◽

David Prenner ◽

Markus Hrachowitz

Keyword(s):

Soil Moisture ◽

Debris Flow ◽

High Intensity ◽

Debris Flows ◽

Regional Scale ◽

Early Summer ◽

Temporal Separation ◽

Antecedent Soil Moisture ◽

Trigger Mechanisms ◽

Debris Flow Initiation

Abstract. Debris flows represent frequent hazards in mountain regions. Though significant effort has been made to predict such events, the trigger conditions as well as the hydrologic disposition of a watershed at the time of debris flow occurrence are not well understood. Traditional intensity-duration threshold techniques to establish trigger conditions generally do not account for distinct influences of rainfall, snowmelt, and antecedent moisture. To improve our knowledge on the connection between debris flow initiation and the hydrologic system at a regional scale, this study explores the use of a semi-distributed conceptual rainfall–runoff model, linking different system variables such as soil moisture, snowmelt, or runoff with documented debris flow events in the inner Pitztal watershed, Austria. The model was run on a daily basis between 1953 and 2012. Analysing a range of modelled system state and flux variables at days on which debris flows occurred, three distinct dominant trigger mechanisms could be clearly identified. While the results suggest that for 68 % (17 out of 25) of the observed debris flow events during the study period high-intensity rainfall was the dominant trigger, snowmelt was identified as the dominant trigger for 24 % (6 out of 25) of the observed debris flow events. In addition, 8 % (2 out of 25) of the debris flow events could be attributed to the combined effects of low-intensity, long-lasting rainfall and transient storage of this water, causing elevated antecedent soil moisture conditions. The results also suggest a relatively clear temporal separation between the distinct trigger mechanisms, with high-intensity rainfall as a trigger being limited to mid- and late summer. The dominant trigger in late spring/early summer is snowmelt. Based on the discrimination between different modelled system states and fluxes and, more specifically, their temporally varying importance relative to each other, this exploratory study demonstrates that already the use of a relatively simple hydrological model can prove useful to gain some more insight into the importance of distinct debris flow trigger mechanisms. This highlights in particular the relevance of snowmelt contributions and the switch between mechanisms during early to mid-summer in snow-dominated systems.

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Discharge of landslide-induced debris flows: case studies of Typhoon Morakot in southern Taiwan

Natural Hazards and Earth System Sciences Discussions ◽

10.5194/nhessd-2-315-2014 ◽

2014 ◽

Vol 2 (1) ◽

pp. 315-346

Author(s):

J.-C. Chen ◽

M.-R. Chuang

Keyword(s):

Debris Flow ◽

Case Studies ◽

Debris Flows ◽

Maximum Flow ◽

Field Investigation ◽

Typhoon Morakot ◽

Flow Discharge ◽

Modeling Software ◽

Southern Taiwan ◽

Deposition Depth

Abstract. Three debris-flow gullies, the Hong-Shui-Xian, Sha-Xin-Kai, and the Xin-Kai-Dafo gullies, located in the Shinfa area of southern Taiwan were selected as case studies of the discharge of landslide-induced debris flows caused by Typhoon Morakot in 2009. The inundation characteristics of the three debris flows, such as the debris-flow volume, the deposition area, maximum flow depth, and deposition depth, were collected by field investigations and simulated using the numerical modeling software FLO-2D. The discharge coefficient cb, defined as the ratio of the debris-flow discharge Qdp to the water-flow discharge Qwp, was proposed to determine Qdp, and Qwp was estimated by a rational equation. Then, cb was calibrated by a comparison between the field investigation and the numerical simulation of the inundation characteristics of debris flows. Our results showed that the values of cb range from 6 to 18, and their values are affected by the landslide ratio The empirical relationships between Qdp and Qwp were also presented.

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A probabilistic model for assessing debris flow propagation at regional scale: a case study in Campania region, Italy

10.5194/egusphere-egu21-2224 ◽

2021 ◽

Author(s):

Luca Crescenzo ◽

Gaetano Pecoraro ◽

Michele Calvello ◽

Richard Guthrie

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Regional Scale ◽

Erosion And Deposition ◽

Campania Region ◽

Source Areas ◽

Model Input ◽

Travel Path ◽

Debris Avalanches ◽

Modelling Approach

Debris flows and debris avalanches are rapid to extremely rapid landslides that tend to travel considerable distances from their source areas. Interaction between debris flows and elements at risk along their travel path may result in potentially significant destructive consequences. One of the critical challenges to overcome with respect to debris flow risk is, therefore, the credible prediction of their size, travel path, runout distance, and depths of erosion and deposition. To these purposes, at slope or catchment scale, sophisticated physically-based models, appropriately considering several factors and phenomena controlling the slope failure mechanisms, may be used. These models, however, are computationally costly and time consuming, and that significantly hinders their applicability at regional scale. Indeed, at regional scale, debris flows hazard assessment is usually carried out by means of qualitative approaches relying on field surveys, geomorphological knowledge, geometric features, and expert judgement.In this study, a quantitative modelling approach based on cellular automata methods, wherein individual cells move across a digital elevation model (DEM) landscape following behavioral rules defined probabilistically, is proposed and tested. The adopted model, called LABS, is able to estimate erosion and deposition soil volumes along a debris flow path by deploying at the source areas autonomous subroutines, called agents, over a 5 m spatial resolution DEM, which provides the basic information to each agent in each time-step. Rules for scour and deposition are based on mass balance considerations and independent probability distributions defined as a function of slope DEM-derived values and a series of model input parameters. The probabilistic rules defined in the model are based on data gathered for debris flows and debris avalanches that mainly occurred in western Canada. This study mainly addresses the applicability and the reliability of this modelling approach to areas in southern Italy, in Campania region, historically affected by debris flows in pyroclastic soils. To this aim, information on inventoried debris flows is used in different study areas to evaluate the effect on the predictions of the model input parameter values, as well as of different native DEM resolutions.

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Debris flows on forested cones – reconstruction and comparison of frequencies in two catchments in Val Ferret, Switzerland

Natural Hazards and Earth System Science ◽

10.5194/nhess-7-207-2007 ◽

2007 ◽

Vol 7 (2) ◽

pp. 207-218 ◽

Cited By ~ 26

Author(s):

M. Bollschweiler ◽

M. Stoffel

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Historical Knowledge ◽

Study Region ◽

Sampling Height ◽

The Alps ◽

Recurrence Intervals ◽

Study Sites ◽

Flow Activity ◽

Different Characteristics

Abstract. Debris flows represent a major threat to infrastructure in many regions of the Alps. Since systematic acquisition of data on debris-flow events in Switzerland only started after the events of 1987, there is a lack of historical knowledge on earlier debris-flow events for most torrents. It is therefore the aim of this study to reconstruct the debris-flow activity for the Reuse de Saleinaz and the La Fouly torrents in Val Ferret (Valais, Switzerland). In total, 556 increment cores from 278 heavily affected Larix decidua Mill., Picea abies (L.) Karst. and Pinus sylvestris L. trees were sampled. Trees on the cone of Reuse de Saleinaz show an average age of 123 years at sampling height, with the oldest tree aged 325 years. Two periods of intense colonization (the 1850s–1880s and the 1930s–1950s) are observed, probably following high-magnitude events that would have eliminated the former forest stand. Trees on the cone of Torrent de la Fouly indicate an average age of 119 years. As a whole, tree-ring analyses allowed assessment of 333 growth disturbances belonging to 69 debris-flow events. While the frequency for the Reuse de Saleinaz study site comprises 39 events between AD 1743 and 2003, 30 events could be reconstructed at the Torrent de la Fouly for the period 1862–2003. Even though the two study sites evince considerably different characteristics in geology, debris-flow material and catchment morphology, they apparently produce debris flows at similar recurrence intervals. We suppose that, in the study region, the triggering and occurrence of events is transport-limited rather than weathering-limited.

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Debris-flow forecasting at regional scale by combining susceptibility mapping and radar rainfall

Natural Hazards and Earth System Science ◽

10.5194/nhess-15-587-2015 ◽

2015 ◽

Vol 15 (3) ◽

pp. 587-602 ◽

Cited By ~ 24

Author(s):

M. Berenguer ◽

D. Sempere-Torres ◽

M. Hürlimann

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Regional Scale ◽

Early Warning Systems ◽

Warning Systems ◽

Susceptibility Assessment ◽

Radar Rainfall ◽

Eastern Pyrenees ◽

Rainfall Map ◽

Rainfall Estimates

Abstract. This work presents a technique for debris-flow (DF) forecasting able to be used in the framework of DF early warning systems at regional scale. The developed system is applied at subbasin scale and is based on the concepts of fuzzy logic to combine two ingredients: (i) DF subbasin susceptibility assessment based on geomorphological variables and (ii) the magnitude of the rainfall situation as depicted from radar rainfall estimates. The output of the developed technique is a three-class warning ("low", "moderate" or "high") in each subbasin when a new radar rainfall map is available. The developed technique has been applied in a domain in the eastern Pyrenees (Spain) from May to October 2010. The warning level stayed "low" during the entire period in 20% of the subbasins, while in the most susceptible subbasins the warning level was at least "moderate" for up to 10 days. Quantitative evaluation of the warning level was possible in a subbasin where debris flows were monitored during the analysis period. The technique was able to identify the three events observed in the catchment (one debris flow and two hyperconcentrated flow events) and produced no false alarm.

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Magnitude estimation of a landslide-triggered debris flow in the Serra do Mar Mountain Range, Brazil

10.5194/egusphere-egu2020-3706 ◽

2020 ◽

Author(s):

Victor Carvalho Cabral ◽

Fernando Mazo D'Affonseca ◽

Marcelo Fischer Gramani ◽

Agostinho Tadashi Ogura ◽

Claudia Santos Corrêa ◽

...

Keyword(s):

Debris Flow ◽

Magnitude Estimation ◽

Cross Sections ◽

Debris Flows ◽

Mountain Range ◽

Serra Do Mar ◽

Solids Concentration ◽

Geomorphic Features ◽

Total Magnitude ◽

Future Events

Debris flows represent great hazard to communities and infrastructures, since they move quickly and are very destructive. In Brazil, debris flows mainly occur in the Serra do Mar Mountain Range, where thousands of casualties were reported in the last two decades due to these phenomena. This study aims at estimating the magnitude of a debris-flow event that occurred in Serra do Mar on February 2017, at the Pedra Branca watershed in the State of Paran&#225;. Debris-flow magnitude refers to the volume of material discharged during an event and is an important aspect of debris-flow hazard assessment. The Pedra Branca event was initiated by rainfall-triggered shallow landslides, damaging local oil pipelines and farms. The magnitude estimation is based on the combination of empirically based equations and the geomorphic features of the debris flow, acquired from in situ and aerial investigation. 28 cross-sections were made along the river channel, considering post-event channel width, erosion and accumulation depth, as well as depositional features. Sediment sources and accumulation areas were identified and delimitated based on high-resolution (1:500) aerial drone photographs. The results indicate that the landslides that initiated the event released approximately 26,884.5 m3 of sediments (Vi) into the main channel of Pedra Branca and that the volume eroded (Ve) and accumulated (Vd) along the channel are, respectively, 82,439 m3 and 22,012 m3. The estimated total solids volume (Vs) is 87,274 m3, assuming that Vs = Vi + Ve - Vd. Moreover, considering a solids concentration of 57% calculated according to empirically-based equations for Serra do Mar, the debris flow had a total magnitude of 153,113 m3. These estimations suggest that the February 2017 debris flow mobilised great volume of material and that 15% of the total volume accumulated on the channel bed, which can be remobilised by future events. Further research on debris-flow dynamics and recurrence at the Serra do Mar Mountain Range is recommended to mitigate future hazards.

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