scholarly journals The December 2012 Mayo River debris flow triggered by Super Typhoon Bopha in Mindanao, Philippines: lessons learned and questions raised

2016 ◽  
Vol 16 (12) ◽  
pp. 2683-2695 ◽  
Author(s):  
Kelvin S. Rodolfo ◽  
A. Mahar F. Lagmay ◽  
Rodrigo C. Eco ◽  
Tatum Miko L. Herrero ◽  
Jerico E. Mendoza ◽  
...  
Keyword(s):  
Climate Change ◽  
Debris Flow ◽  
Population Growth ◽  
Debris Flows ◽  
Lessons Learned ◽  
Loss Of Life ◽  
River Watershed ◽  
Super Typhoon ◽  
Future Events ◽  
The Village

Abstract. Category 5 Super Typhoon Bopha, the world's worst storm of 2012, formed abnormally close to the Equator, and its landfall on Mindanao set the record proximity to the Equator for its category. Its torrential rains generated an enormous debris flow in the Mayo River watershed that swept away much of the village Andap in the New Bataan municipality, burying areas under rubble as thick as 9 m and killing 566 people. Established in 1968, New Bataan had never experienced super typhoons and debris flows. This unfamiliarity compounded the death and damage. We describe Bopha's history, debris flows and the Mayo River disaster, and then we discuss how population growth contributed to the catastrophe, as well as the possibility that climate change may render other near-Equatorial areas vulnerable to hazards brought on by similar typhoons. Finally, we recommend measures to minimize the loss of life and damage to property from similar future events.

scholarly journals The December 2012 Mayo River debris flow triggered by Super Typhoon Bopha in Mindanao, Philippines: Lessons learned and questions raised

2016 ◽  
Author(s):  
Kelvin S. Rodolfo ◽  
A. Mahar F. Lagmay ◽  
R. Narod Eco ◽  
Tatum Miko L. Herrero ◽  
Jerico E. Mendoza ◽  
...  
Keyword(s):  
Climate Change ◽  
Debris Flow ◽  
Population Growth ◽  
Debris Flows ◽  
Lessons Learned ◽  
Loss Of Life ◽  
River Watershed ◽  
Super Typhoon ◽  
Future Events

Abstract. Category 5 Super Typhoon Bopha, the world's worst storm of 2012, formed abnormally close to the Equator, and its landfall on Mindanao set the record proximity to the Equator for its category. Its torrential rains generated an enormous debris flow in the Mayo River watershed that swept away much of Andap village in New Bataan municipality, burying areas under rubble as thick as 9 meters and killing 566 people. Established in 1968, New Bataan had never experienced super typhoons and debris flows. This unfamiliarity compounded the death and damage. We describe Bopha's history, debris flows and the Mayo River disaster, then discuss how population growth contributed to the catastrophe, and the possibility that climate change may render other near-Equatorial areas vulnerable to hazards brought by similar typhoons. Finally, we recommend measures to minimize the loss of life and damage to property from similar, future events.

Alternative approach for works controlling stony debris flows

2020 ◽  
Author(s):  
Carlo Gregoretti ◽  
Matteo Barbini ◽  
Martino Bernard ◽  
Mauro Boreggio
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
High Elevation ◽  
Valley Bottom ◽  
Check Dams ◽  
Retention Basin ◽  
Retention Basins ◽  
Solid Liquid ◽  
The Impact ◽  
The Village

<p>Many sites of the Dolomites are threatened by channelized debris flows: solid-liquid surges initiated by the entrainment of large quantities of sediments into the abundant runoff at the head of channel incised on fans, can dramatically increase their volume along the downstream routing. This is the case of the Rovina di Cancia site where solid-liquid surges forming in the upper part of the basin can increase their volume up and over 50000 m<sup>3</sup>, seriously impacting the downstream village of Borca di Cadore. The debris-flow channel ends just upstream the village that in the past was hit by four debris flows (three in the recent years) that caused victims and destructions. Control works built until now are not sufficient to protect the village from high magnitude debris flows and a definitive solution calls to be planned. Present works are a flat deposition area, 300 m downstream the initiation area, an open dam under construction downstream it, and  two retention basins at the end of the channel. Between the open dam and the upstream retention basin, there are the rest of eight check-dams made of gabions, built in the 60s and progressively damaged or destroyed by the debris flows occurred after their construction. This series of check-dams limited the entrainment of solid material and the occurrence of localized scours. The initial plan is the substitution of the check-dams with concrete structures and the widening of the dowsntream retention basin through the raising of high elevation embankment downstream it and the following demolition of the actual dyke. Finally, a channel crossing the village and national route on the valley bottom will deliver the fluid phase from the widened basin to the Boite river. All these control works have a very high cost for construction and maintenance and severely impact the village with the presence of a non-negligible residual risk. These drawbacks call for an alternative solution that is searched looking at to the morphology. Downstream of the open dam and on its right side, there is a deep impluvium that ends on a large grass sloping area. The novel solution requires the construction of a channel through the right high bank that deviates the debris flow into the impluvium. The impluvium, widened through the excavation of the surrounding slopes, is closed at the outlet by  an open dam. Downstream the open dam, a channel will lead to a retention basin, where most of storage volume is obtained from the excavation of the grass sloping area, limiting the elevation of the dykes At the end of this basin an open dam will deliver the debris-flow fluid part to a channel passing under the national route and joining the Boite river. Such a solution composed of a deviatory channel, two retention basins (the deep impluvium and that excavated on the sloping grass area) and the channels between and downstream them, has quite a lower costs of construction and maintenance, eliminating the impact on the village because occupying uninhabited areas without interrupting the main roads.</p>

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

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

<p><span>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 Paraná. 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 <em>in situ</em> 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 m<sup>3</sup> of sediments (V<sub>i</sub>) into the main channel of Pedra Branca and that the volume eroded (V<sub>e</sub>) and accumulated (V<sub>d</sub>) along the channel are, respectively, 82,439 m<sup>3</sup> and 22,012 m<sup>3</sup>. The estimated total solids volume (V<sub>s</sub>) is 87,274 m<sup>3</sup>, assuming that V<sub>s</sub> = V<sub>i</sub> + V<sub>e</sub> - V<sub>d</sub>. 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 m<sup>3</sup>. 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.</span></p>

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.

Climate change impacts on sediment yield and debris-flow activity at the Illgraben, Switzerland

2020 ◽  
Author(s):  
Jacob Hirschberg ◽  
Simone Fatichi ◽  
Georgie Bennett ◽  
Brian McArdell ◽  
Stuart Lane ◽  
...  
Keyword(s):  
Climate Change ◽  
Debris Flow ◽  
Surface Runoff ◽  
Debris Flows ◽  
Cascade Model ◽  
Weather Generator ◽  
Climate Scenarios ◽  
Climate Services ◽  
The Future ◽  
Flow Activity

<p>Debris flows are rapid mass movements composed of a mixture of water and sediments and often pose a danger to humans and infrastructure. In the Alpine environment, they are mostly triggered by intense rainfall, snowmelt or a combination thereof, and conditioned by sediment availability. Their occurrence is expected to increase in a warmer climate due to changes in the hydrological regime (e.g. higher rainfall intensity, lower duration of snow cover). Furthermore, sediment production is likely to accelerate due to permafrost thawing and changes in freeze-thaw cycles, resulting in increased sediment availability. For the purpose of climate change impact assessment on sediment yield and debris-flow activity, interactions and feedbacks of climate and the aforementioned processes need to be considered jointly.</p><p>In the study presented here, we address this challenge by forcing a sediment cascade model (SedCas<sup>1</sup>) with precipitation and temperature from a stochastic weather generator (AWE-GEN<sup>2</sup>) producing ensembles of possible climate in the present and for the future. The chosen study site is the Illgraben, a debris-flow prone catchment in the Swiss Alps which currently produces 3-4 debris flows yearly on average. SedCas conceptualizes a geomorphic system in which hillslopes produce and store sediments from landslides and eventually deliver them to the channels. From there, sediments can be mobilized by concentrated surface runoff and transferred out of the catchment in form of bedload, hypreconcentrated flow, or debris flows, depending on the surface runoff magnitude and the sediment availability. AWE-GEN operates at the hourly scale and is trained for the current climate with observed data and for the future climate using the newest climate change projections for Switzerland CH2018 developed by the National Center for Climate Services<sup>3</sup>.</p><p>Preliminary results reveal a likely increase in debris-flow occurrence in the Illgraben in the future. Such an increase can be attributed to an extension in the debris-flow seasonal changes in the discharge regime. Furthermore, the number of landslides filling the sediment storage increases because they are affected by a shorter duration of snow cover and thus greater exposure to freeze-thaw weathering. However, projections are subject to large uncertainties, stemming not only from uncertainty in climate scenarios, but also from internal climate variability. Furthermore, the simplified hillslope weathering and debris-flow triggering mechanisms contribute to the overall uncertainty. Nevertheless, the methodology is thought to be transferable to any sediment-cascade-like catchment where dominant processes are driven by climate. Lastly, this work highlights the importance of considering stochasticity in climate and sediment history for projections of magnitudes and frequencies of relative rare events as debris flows. This allows us to explicitly separate climate change signals in geomorphic processes from fluctuations induced by internal natural variability.</p><p>REFERENCES</p><p><sup>1</sup> Bennett, G. L., et al. "A probabilistic sediment cascade model of sediment transfer in the Illgraben." Water Resources Research 50.2 (2014): 1225-1244. doi: 10.1002/2013WR013806</p><p><sup>2</sup> Fatichi, S., et al. "Simulation of future climate scenarios with a weather generator." Advances in Water Resources 34.4 (2011): 448-467. doi: 10.1016/j.advwatres.2010.12.013</p><p><sup>3</sup> CH2018 - Climate Scenarios for Switzerland. National Centre for Climate Services (2018): doi: 10.18751/Climate/Scenarios/CH2018/1.0</p>

scholarly journals Simulation of debris flows in the watershed of the Putih River, Indonesia using SIMLAR 2.1

2021 ◽  
Vol 930 (1) ◽  
pp. 012034
Author(s):  
J Ikhsan ◽  
R Ardiansyah ◽  
D Legono
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Rainfall Data ◽  
River Watershed ◽  
Volcanic Material ◽  
Flow Modelling ◽  
Dam Building ◽  
Sediment Data ◽  
The Impact

Abstract In 2010, the eruption of Mount Merapi produced a huge volcanic material for debris flows. One area affected by the debris flows is the watershed of Putih River. To predict the impact caused by debris flows can be done by using software such as the Simulation Lahar (SIMLAR) 2.1. In this paper, debris flow modelling will be carried out using SIMLAR 2.1 in conditions without sabo dams and using sabo dams. This simulation aims to determine the effectiveness of the sabo dams in reducing the impact of debris flows. The data used are rainfall data, DEM and sediment data in Putih River. The results show that the sabo dam building can slow down the velocity of debris flow. In addition, sabo dams also function as a barrier to riverbed erosion in the Putih River watershed. Based on the results above, it can be concluded that SIMLAR 2.1 can predict the impact of debris flows in the Putih River watershed.

scholarly journals Mechanisms of Initiation, Runout, and Rainfall Thresholds of Extreme-Precipitation-Induced Debris Flows

2021 ◽  
Author(s):  
Srikrishnan Siva Subramanian ◽  
Ali. P. Yunus ◽  
Faheed Jasin ◽  
Minu Treesa Abraham ◽  
Neelima Sathyam ◽  
...  
Keyword(s):  
Debris Flow ◽  
Extreme Precipitation ◽  
Debris Flows ◽  
Maximum Velocity ◽  
Rainfall Threshold ◽  
Rainfall Thresholds ◽  
Long Runout ◽  
Loss Of Life ◽  
Extreme Precipitation Events ◽  
Precipitation Events

Abstract The frequency of unprecedented extreme precipitation events is increasing, and consequently, catastrophic debris flows occur in regions worldwide. Rapid velocity and long-runout distances of debris flow induce massive loss of life and damage to infrastructure. Despite extensive research, understanding the initiation mechanisms and defining early warning thresholds for extreme-precipitation-induced debris flows remain a challenge. Due to the nonavailability of extreme events in the past, statistical models cannot determine thresholds from historical datasets. Here, we develop a numerical model to analyze the initiation and runout of extreme-precipitation-induced runoff-generated debris flows and derive the Intensity-Duration (ID) rainfall threshold. We choose the catastrophic debris flow on 6 August 2020 in Pettimudi, Kerala, India, for our analysis. Our model satisfactorily predicts the accumulation thickness (7 m to 8 m) and occurrence time of debris flow compared to the benchmark. Results reveal that the debris flow was rapid, traveling with a maximum velocity of 9 m/s for more than 9 minutes. The ID rainfall threshold defined for the event suggests earlier thresholds are not valid for debris flow triggered by extreme precipitation. The methodology we develop in this study is helpful to derive ID rainfall thresholds for debris flows without historical data.

Assessment of the 2019 Chamoson debris flow event (Swiss Alps)

2020 ◽  
Author(s):  
Marc-Henri Derron ◽  
Valérie Baumann ◽  
Tiggi Choanji ◽  
François Noël ◽  
Ludovic Baron ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Heavy Rain ◽  
Peak Discharge ◽  
Swiss Alps ◽  
Mitigation Measures ◽  
Size Classification ◽  
Cone Apex ◽  
The Right ◽  
The Village

<p>Debris flows triggered by heavy rain are common and can cause huge damages in Alpine valleys. In this case we documented the changes occurred in the Losentsé valley after the 11 August 2019 event, which caused two death and several damages to the village of Chamoson. The Chamoson basin is located in the Alps on the right side of the Rhône valley. Three main rivers drain the Chamoson basin, the Losentsé, the Cry and the Tsené. The main debris flow event occurred in the Losentsé sub-basin. The Losentsé River is 9 km long from the sources at 3000 m until the alluvial cone apex at 600 m. In the upper part of the Chamoson basin thick loose debris cones and glacial deposits lie on steep slopes, the geology of the middle basin is formed by unstable clayey shales with several active landslides on both lateral valley slopes.</p><p>The village of Chamoson is located on the huge alluvial cone built with torrential events from the three main rivers. Since the XIX century, several big debris flow events (1898, 1923, 2003, 2018) were recorded in this area and mitigation measures were built in the principal rivers. Unfortunately, the 2019 debris flows overflowed the channels limit when the flows reached the alluvial cone apex, reaching the road and took a car with 2 persons inside. Upstream in the middle basin 2 wood bridges were destroyed and many concrete or stone walls (mitigation measures) along the river were damaged.</p><p>After the event we acquired pictures with a drone from the sources area and the Losentsé river valley in order to have a post event image. With this image we could analyse and map the source areas and the inundated areas in the Losentsé channel. We did also field observation along the river.</p><p>After comparing the pre- and post-event images we mapped the middle and upper basin inundated areas by the 2019 event and the described the deposits and eroded sections along the river. We calculated the peak discharge of 1000 m<sup>3</sup>/s for this event using the inundated transversal profile area near the cone apex and the flow velocity obtained from a movie. The peak discharge corresponds to 4 in the size classification for debris flows (Jacob et al., 2005).</p><p>Reference:</p><p>Jakob, M. (2005). A size classification for debris flows. Engineering geology, 79(3-4), 151-161.</p>

scholarly journals Numerical simulation of debris flows triggered from the Strug rock fall source area, W Slovenia

2006 ◽  
Vol 6 (2) ◽  
pp. 261-270 ◽  
Author(s):  
M. Mikoš ◽  
R. Fazarinc ◽  
B. Majes ◽  
R. Rajar ◽  
D. Žagar ◽  
...  
Keyword(s):  
Debris Flow ◽  
Mathematical Models ◽  
Debris Flows ◽  
Model Calibration ◽  
Source Area ◽  
Rock Fall ◽  
One Dimensional ◽  
Engineering Measures ◽  
The Village ◽  
Extreme Scenario

Abstract. The Strug landslide was triggered in December 2001 as a rockslide, followed by a rock fall. In 2002, about 20 debris flows were registered in the Kosec village; they were initiated in the Strug rock fall source area. They all flowed through the aligned Brusnik channel, which had been finished just before the first debris flow reached the village in April 2002. Debris flow events were rainfall-induced but also governed by the availability of rock fall debris in its zone of accumulation. After 2002 there was not enough material available for further debris flows to reach the village. Nevertheless, a decision was reached to use mathematical modeling to prepare a hazard map for the village for possible new debris flows. Using the hydrological data of the Brusnik watershed and the rheological characteristics of the debris material, 5 different scenarios were defined with the debris flow volumes from 1000 m3 to a maximum of 25 000 m3. Two mathematical models were used, a one-dimensional model DEBRIF-1D, and a two-dimensional commercially available model FLO-2D. Due to the lack of other field data, data extracted from available professional films of debris flows in 2002 in the Kosec village were used for model calibration. The computational reach was put together from an 800-m long upstream reach and 380-m long regulated reach of the Brusnik channel through the village of Kosec. Both mathematical models have proved that the aligned Brusnik channel can convey debris flows of the volume up to 15 000 m3. Under the most extreme scenario a debris flow with 25 000 m3 would locally spill over the existing levees along the regulated Brusnik channel. For this reason, additional river engineering measures have been proposed, such as the raising of the levees and the construction of a right-hand side sedimentation area for debris flows at the downstream end of the regulated reach.

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