scholarly journals Sedimentology, dynamics and debris flow potential of Champadevi River, southwest Kathmandu, Nepal

1970 ◽  
Vol 10 ◽  
pp. 9-20
Author(s):  
Naresh Kazi Tamrakar ◽  
Achut Prajapati ◽  
Suman Manandhar
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Alluvial Fan ◽  
Shear Stresses ◽  
Stream Power ◽  
Huge Amount ◽  
Sedimentary Characteristics ◽  
Unconsolidated Material ◽  
Flow Potential ◽  
Headward Erosion

Mountainous and hilly regions are potential for debris flows, one of the major forms of natural disasters, which cause serious damage in downstream areas. The southwestern region of the Kathmandu Valley experienced catastrophic flows in the Champadevi River and its two tributaries (the Aitabare and the Raute Rivers) in July 2002. These rivers were investigated for morphologic, hydraulic and sedimentary characteristics to evaluate potential of debris flow in the area. The Raute and the Aitabare Rivers have tendency of headward erosion due to abrupt drop of gradient down the scarp of the alluvial fan deposit composed of unconsolidated matrix-supported gravel and mud. Because of this tendency, the rivers erode their substrate and banks, and contribute slope movements by sheding a huge amount of clasts and matrix. Therefore, instability condition of rivers and unconsolidated material available in the river courses potentially contribute for debris flow. The tractive shear stresses in the Aitabare, the Raute and the Champadevi Rivers (1.27, 1.60 and 0.48 KPa, respectively) exceeds twice the critical shear stresses required to transport 90th-percentile fraction of the riverbed material (0.14, 0.18 and 0.11 KPa). The stream powers (10.8, 17.2 and 5.1 m-kN/s/m2) of these rivers also greatly exceed the critical stream powers (0.21, 0.35 and 0.18 m-kN/s/m2) required to initiate traction transport. Because the tractive shear stresses and the stream powers that are achieved during bankfull flow are several times larger than the corresponding critical values, even the flow having stream power exceeding the critical stream power may potentially generate debris flow.   doi: 10.3126/bdg.v10i0.1416 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 9-20

Mechanism of Debris Flows in Mountain Streams

2013 ◽  
Vol 419 ◽  
pp. 883-888
Author(s):  
Chang Huan Kou ◽  
Shih Wei Ma ◽  
Meng Wei Lai
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Dimensionless Parameter ◽  
Transient Behavior ◽  
Mountain Streams ◽  
Shear Stresses ◽  
Huge Amount ◽  
Flow Development ◽  
Initial Stage ◽  
Flood Flow

This paper suggests the mechanism of occurrence of debris flow in mountain streams. It is found that the sliding of the undermined stream banks follows the exponential probability distribution function. This indicates that the major amount of debris is from an intensive sliding in the initial stage of flood flow development. This can be otherwise proved by the viscous flow boundary layer theory such as the shear stresses on the wall are initially very large. Through a relative dimensional analysis, a special dimensionless parameter K is grouped which has a very important effect on the occurrence of the acceleration of the heavy debris by the flow. It interprets, during the flood flow development, the amount of debris on the stream bed can only be accelerated when the kinetic energy of the flow is greater than the apparent work of the debris against the flow. Of course, as a transient behavior, once it starts, the sudden acceleration of a huge amount of debris flow bore will usually cause an unpredictable downstream disaster.

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

2011 ◽  
Vol 11 (5) ◽  
pp. 1247-1257 ◽  
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.

scholarly journals Atmospheric circulation patterns, cloud-to-ground lightning, and locally intense convective rainfall associated with debris flow initiation in the Dolomite Alps of northeastern Italy

2016 ◽  
Vol 16 (2) ◽  
pp. 509-528 ◽  
Author(s):  
S. Jeffrey Underwood ◽  
Michael D. Schultz ◽  
Metteo Berti ◽  
Carlo Gregoretti ◽  
Alessandro Simoni ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Lightning Flash ◽  
Synoptic Scale ◽  
Convective Rainfall ◽  
Spatial And Temporal Scales ◽  
Circulation Patterns ◽  
Unconsolidated Material ◽  
Northeastern Italy ◽  
Debris Flow Initiation

Abstract. The Dolomite Alps of northeastern Italy experience debris flows with great frequency during the summer months. An ample supply of unconsolidated material on steep slopes and a summer season climate regime characterized by recurrent thunderstorms combine to produce an abundance of these destructive hydro-geologic events. In the past, debris flow events have been studied primarily in the context of their geologic and geomorphic characteristics. The atmospheric contribution to these mass-wasting events has been limited to recording rainfall and developing intensity thresholds for debris mobilization. This study aims to expand the examination of atmospheric processes that preceded both locally intense convective rainfall (LICR) and debris flows in the Dolomite region. 500 hPa pressure level plots of geopotential heights were constructed for a period of 3 days prior to debris flow events to gain insight into the synoptic-scale processes which provide an environment conducive to LICR in the Dolomites. Cloud-to-ground (CG) lightning flash data recorded at the meso-scale were incorporated to assess the convective environment proximal to debris flow source regions. Twelve events were analyzed and from this analysis three common synoptic-scale circulation patterns were identified. Evaluation of CG flashes at smaller spatial and temporal scales illustrated that convective processes vary in their production of CF flashes (total number) and the spatial distribution of flashes can also be quite different between events over longer periods. During the 60 min interval immediately preceding debris flow a majority of cases exhibited spatial and temporal colocation of LICR and CG flashes. Also a number of CG flash parameters were found to be significantly correlated to rainfall intensity prior to debris flow initiation.

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.

scholarly journals Atmospheric circulation patterns, cloud-to-ground lightning, and locally intense convective rainfall associated with debris flow initiation in the Dolomite Alps of northeastern Italy

2015 ◽  
Vol 3 (9) ◽  
pp. 5717-5775
Author(s):  
S. J. Underwood ◽  
M. D. Schultz ◽  
M. Berti ◽  
C. Gregoretti ◽  
A. Simoni ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Lightning Flash ◽  
Synoptic Scale ◽  
Convective Rainfall ◽  
Spatial And Temporal Scales ◽  
Circulation Patterns ◽  
Unconsolidated Material ◽  
Northeastern Italy ◽  
Debris Flow Initiation

Abstract. The Dolomite Alps of northeastern Italy experience debris flows with great frequency during the summer months. An ample supply of unconsolidated material on steep slopes and a summer season climate regime characterized by recurrent thunderstorms combine to produce an abundance of these destructive hydrogeologic events. In the past debris flow events have been studied primarily in the context of their geologic and geomorphic characteristics. The atmospheric contribution to these mass wasting events has been limited to recording rainfall and developing intensity thresholds for debris mobilization. This study aims to expand the examination of atmospheric processes that preceded both locally intense convective rainfall (LICR) and debris flows in the Dolomite region. 500 hPa pressure level plots of geopotential heights were constructed for a period of three days prior to debris flow events to gain insight into the synoptic scale processes which provide an environment conducive to LICR in the Dolomites. Cloud-to-ground (CG) lightning flash data recorded at the meso-scale were incorporated to assess the convective environment proximal to debris flow source regions. Twelve events were analyzed and from this analysis three common synoptic scale circulation patterns were identified. Evaluation of CG flashes at smaller spatial and temporal scales illustrated that convective processes vary in their production of CG flashes (total number) and the spatial distribution of flashes can also be quite different between events over longer periods. During the 60 min interval immediately preceding debris flow a majority of cases exhibited spatial and temporal collocation of LICR and CG flashes. Also a number of CG flash parameters were found to be significantly correlated to rainfall intensity prior to debris flow initiation.

Proposal of Estimation Method for Debris Flow Potential Considering Eruptive Activity

2019 ◽  
Vol 14 (1) ◽  
pp. 126-134 ◽  
Author(s):  
Masato Iguchi ◽  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Volcanic Ash ◽  
Ground Deformation ◽  
Estimation Method ◽  
Summit Crater ◽  
Point Load ◽  
Total Weight ◽  
Eruptive Activity ◽  
Flow Potential

An estimation method for debris flow potential is proposed to evaluate the possibility of the occurrence of rain-triggered debris flows. Sakurajima volcano has repeatedly erupted (Vulcanian type) and has continuously emitted volcanic ash at the Minamidake summit crater or Showa crater east of the summit since 1955, and debris flows have frequently occurred at rates of 10 to 111 events per year. Ground deformation associated with debris flows along the Arimura River were analyzed for the period from 2009 to 2016. Downward tilt (10–450 nrad) in the direction of the river and extensional strain (3–138 nstrain) were detected during occurrence of the debris flows. The tilt and strain changes were modeled using a point load caused by debris flow deposition beside a sabo dam. Depositional weights of individual debris flow events were estimated to range from 6 to 276 kt. The total weight of the debris flows was 2,154 kt, which is approximately 5% of the total weight of volcanic ash ejected from the craters during the study period. Debris flow potential (DFP) was defined as the difference in the volcanic ash deposits along the upper stream of the river (5% of the total) and the lower stream of the river, and the temporal change of the debris flow potential was investigated. When the debris flow potential reached a level of 0.4 Mt resulting from an increase in eruptive activity, debris flows frequently occurred or large debris flows were induced during rainy seasons. The concept of debris flow potential was applied to volcanoes in Indonesia as lahar potential. After the 2010 eruption at Merapi volcano, lahar potential, perhaps, quasi-exponentially decays during the dormant period. The lahar potential of Sinabung volcano complicatedly varies because of long-term eruptivity beginning in 2014.

Debris Flow Hazards and its Mitigation Works in Xianbuleng Gully, Jinchuan County, Sichuan Province, China

2012 ◽  
Vol 166-169 ◽  
pp. 2769-2773
Author(s):  
Jin Feng Liu ◽  
Yong You ◽  
Xing Chang Chen
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Case Analysis ◽  
Sichuan Province ◽  
Alluvial Fan ◽  
Drainage Canal ◽  
Hydraulic Condition ◽  
Township Government

This paper presented a case analysis of debris flow hazards and its mitigation works. The Xianbuleng Gully which is located in Jinchuan County, Sichuan Province was selected as study area. This gully is an old debris flow gully which once burst out many debris flow disasters in history. If debris flows occur again in this gully, the township government, the center school and 13 village houses nearly 300 persons on the alluvial fan will be exposed to great risk.The environment settings and the hazard characteristics of the Xianbuleng debris flow were introduced first in this paper. Then, mitigation works especially the drainage canal under the optimal hydraulic condition were planned and designed in the gully for decreasing the debris flow hazards.

Alluvial Fan Alteration Due to Debris-Flow Deposition, Incision, and Channel Migration at Forest Falls, California

2021 ◽  
Vol 27 (1) ◽  
pp. 29-41
Author(s):  
Kerry Cato ◽  
Brett Goforth
Keyword(s):  
Debris Flow ◽  
Water Content ◽  
Debris Flows ◽  
Dynamic Instability ◽  
Debris Avalanche ◽  
Alluvial Fan ◽  
Multiple Sources ◽  
Sediment Delivery ◽  
Field Methods ◽  
San Bernardino Mountains

ABSTRACT Historical patterns of debris flows have been reconstructed at the town of Forest Falls in the San Bernardino Mountains using a variety of field methods (mapping flow events after occurrence, dendrochronology evidence, soil chronosequences). Large flow events occur when summer thunderstorms produce brief high-intensity rainfall to mobilize debris; however, the geomorphic system exhibits properties of non-linear response rather than being a single-event precipitation-driven process. Previous studies contrasted the relative water content of flows generated by varying-intensity summer thunderstorms to model factors controlling flow velocity and pathway of deposition. We hypothesize that sediment discharge in this geomorphic system exhibits multiple sources of complexity and present evidence of (1) thresholds of sediment delivery from sources at the higher reaches of bedrock canyons, (2) storage effects in sediment transport down the bedrock canyons, and (3) feedbacks in deposition, remobilization, and transport of sediment across the alluvial fan in dynamic channel filling, cutting, and avulsion processes. An example of the first component occurred in March 2017, when snowmelt generated a rapid translational landslide and debris avalanche of about 80,000 m3; this sediment was deposited in the bedrock canyon but moved no farther down gradient. The second component was observed when accumulation of meta-stable sediments in the bedrock canyon remained in place until fluvial erosion and subsequent debris flow provided dynamic instability to remobilize the mass downstream. The third component occurred on the alluvial fan below the bedrock canyon, where low-water-content debris flows deposited sediments that filled the active channel, raising the channel grade level to levee elevation, allowing for subsequent spread of non-channelized flows onto the fan surface and scouring new channel pathways down fan. A conceptual model of spatial and temporal complexities in this debris-flow system is proposed to guide future study for improved risk prediction.

scholarly journals The application of numerical debris flow modelling for the generation of physical vulnerability curves

2011 ◽  
Vol 11 (7) ◽  
pp. 2047-2060 ◽  
Author(s):  
B. Quan Luna ◽  
J. Blahut ◽  
C. J. van Westen ◽  
S. Sterlacchini ◽  
T. W. J. van Asch ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Integrated Approach ◽  
Quadratic Model ◽  
Internal Stresses ◽  
Shear Stresses ◽  
Flow Depth ◽  
Physical Vulnerability ◽  
Physical Damage ◽  
Lombardy Region

Abstract. For a quantitative assessment of debris flow risk, it is essential to consider not only the hazardous process itself but also to perform an analysis of its consequences. This should include the estimation of the expected monetary losses as the product of the hazard with a given magnitude and the vulnerability of the elements exposed. A quantifiable integrated approach of both hazard and vulnerability is becoming a required practice in risk reduction management. This study aims at developing physical vulnerability curves for debris flows through the use of a dynamic run-out model. Dynamic run-out models for debris flows are able to calculate physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk could suffer an impact. These results can then be applied to consequence analyses and risk calculations. On 13 July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of the Valtellina Valley (Lombardy Region, Northern Italy). One of the largest debris flows events occurred in a village called Selvetta. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. The Selvetta event was modelled with the FLO-2D program, an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. The behaviour and run-out of the flow was reconstructed. The significance of calculated values of the flow depth, velocity, and pressure were investigated in terms of the resulting damage to the affected buildings. The physical damage was quantified for each affected structure within the context of physical vulnerability, which was calculated as the ratio between the monetary loss and the reconstruction value. Three different empirical vulnerability curves were obtained, which are functions of debris flow depth, impact pressure, and kinematic viscosity, respectively. A quantitative approach to estimate the vulnerability of an exposed element to a debris flow which can be independent of the temporal occurrence of the hazard event is presented.

scholarly journals Sedimentological characteristics of debris flow Deposits within ice−cored moraine of Ebbabreen, central Spitsbergen

2015 ◽  
Vol 36 (2) ◽  
pp. 125-144 ◽  
Author(s):  
Krzysztof Pleskot
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Slope Angle ◽  
Parent Material ◽  
Original Structure ◽  
Sediment Layer ◽  
Local Conditions ◽  
Thin Sections ◽  
Sedimentary Characteristics ◽  
Deposition Area

Abstract The Ebbabreen ice−cored moraine area is covered with a sediment layer of up to 2.5 m thick, which mostly consists of massive diamicton. Due to undercutting by lateral streams, debris flow processes have been induced in marginal parts of this moraine. It was recognized that the sedimentology of deposits within the deposition area of debris flows is the effect of: (1) the origin of the sediments, (2) the nature of the debris flow, and (3) post−debris flow reworking. Analysis of debris flow deposits in microscale (thin sections) suggests a common mixing during flow, even though a small amount of parent material kept its original structure. The mixing of sediments during flow leads to them having similar sedimentary characteristics across the deposition area regardless of local conditions (i.e. slope angle, water content, parent material lithology). After the deposition of sediments that were transported by the debris flow, they were then reworked by a further redeposition process, primarily related to meltwater stream action.

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