Characteristics Of Debris Flow Research Articles

Analysis of material supply characteristics of debris flow based on land use types in the upper Min River, China

Land-use type is a natural choice of human social and economic activities. This study investigates the typical debris flow gullies of the upper Min River and analyses the supply characteristics and activity of its material sources under various land-use types using multi-stage remote sensing images data and geographic information system software. The results demonstrate the following: (1) the land-use type does not restrict the loose material source of debris flow near the fault zone; (2) the degree of cultivated land, forest (grass) land, bare land, and urban and rural construction land promote debris flow disaster formation in different channels far from the fault zone; (3) the gully exhibits significant influence on human engineering activities, and there are more loose material sources between the bare land and urban and rural construction land; (4) more loose material sources are observed in forest (grass) land and cultivated land in debris flow channels with vegetation development. In summary, before the Wenchuan earthquake, the debris flow source centroid is far from the debris flow channel, but after the earthquake, the debris flow material source centroid is near the debris flow channel.

Deposition characteristics of debris flows in a lateral flume considering upstream entrainment

The sediment deposited by debris flows in rivers is a common cause of mountain disasters. The deposition characteristics of debris flows are strongly affected by the entrainment during the transportation process and the water depth in the river channel, but how is poorly understood. Here, the effects of the released flow volume, flow density, bed sediment and water depth on the deposition process of debris flows are investigated for a total of 22 different tests. Detailed topographic surveys of deposit lobes are conducted using a 3D laser scanner with high precision. The slopes of lobes are largely determined by the flow density and bed-sediment composition. However, the effect of released flow volume on the lobe slope is relatively limited. The lobe areas projected onto the horizontal plane display dumbbell or trapezoidal shapes depending on deposit volume, and the cross sections along the lateral flume present a Gaussian distribution for flows after bed-sediment entrainment. The lobe area is reduced and lobe height is enhanced with an increase of water depth, contributing to a steeper deposit. Partial, submersed or complete blockages occur, depending on the debris-flow volume and water depth. This study improves understanding of the deposition features and may aid future hazard assessments of debris flows.

Laboratory Analysis of Debris Flow Characteristics and Berm Performance

In this study, laboratory tests were used to determine the deposition characteristics (runout distance, lateral width, and deposition area) of debris flow and their relationships with the flow characteristics (flow velocity and flow depth) according to the presence of a berm. An experimental flume 1.3 to 1.9 m long, 0.15 m wide, and 0.3 m high was employed to investigate the effects of channel slope and volumetric concentration of sediment with and without the berm. The runout distance (0.201–1.423 m), lateral width (0.045–0.519 m), and deposition area (0.008–0.519 m2) increased as the channel slope increased and as the volumetric concentration of sediment decreased. These quantities also increased with the flow velocity and flow depth. In addition, the maximum reductions in the runout distance, lateral width, and deposition area were 69.1%, 65.9%, and 93%, respectively, upon berm installation. The results of this study illustrate general debris flow characteristics according to berm installation; the reported relationship magnitudes are specific to the experimental conditions described herein. However, the results of this study contribute to the design of site-specific berms in the future by providing data describing the utility and function of berms in mitigating debris flow.

Temporal Characteristics of Debris Flow Surges

Debris flow is one of the most destructive geomorphological events in mountainous watersheds, which usually appears in the form of successive surge waves as observed all over the world. In particular, debris flows in the Jiangjia Gully in southwest China have displayed a great variety of surge phenomena; each debris flow event contains tens or hundreds of separate surges originating from different sources. Therefore, the surge sequence of an event must encode the information of debris flow developing. The unmanned aerial vehicle photos provide an overview of debris flow sources, showing the different potentials of the debris flow and surge sequences present various patterns responding to the rainfall events. Then the variety of rainfalls and material sources determine the diversity of surge sequence. Using time series analysis to the surge discharge sequences, we calculate the Hurst exponent, the autocorrelation function, and the power spectrum exponent and find that all the sequences commonly share the property of long-term memory and these parameters are correlated in an exponential form, with values depending on rainfall patterns. Moreover, all events show a gross trend of discharge decay, despite the local rainfall process, which implies the intrinsic nature of the surge sequence as a systematic behavior of watershed. It is expected that these findings are heuristic for establishing mechanisms of debris flow initiation and evolution in a watershed.

Debris Flow Characteristics in Flume Experiments Considering Berm Installation

This study was conducted to identify the characteristics and mobility of debris flows and analyze the performance of a berm as a debris flow mitigation measure. The debris flow velocity, flow depth, Froude number, flow resistance coefficients, and mobility ratio were accordingly determined using the results of flume tests. To analyze the influence of the berm, the results for a straight channel test without a berm were compared with those for a single-berm channel test. The debris flow velocity was observed to increase with increasing channel slope and decreasing volumetric concentration of sediment, whereas the mobility ratio was observed to increase with increasing channel slope and volumetric concentration of sediment. In addition, it was confirmed that the installation of a berm significantly decreased the debris flow velocity and mobility ratio. This indicates that a berm is an effective method for reducing damage to areas downstream of a debris flow by decreasing its potential mobility. By identifying the effects of berms on debris flow characteristics according to the channel slope and volumetric concentration of sediment, this study supports the development of berms to serve as debris flow damage mitigation measures.

Change Detection and Feature Extraction of Debris-Flow Initiation by Rock-Slope Failure Using Point Cloud Processing

Our understanding of debris-flow initiation by slope failure is restricted by the challenge of acquiring accurate geomorphic features of debris flows and the structural setting of the rock mass in the remote mountainous terrain. Point cloud data of debris flows in Sabino Canyon, Tucson, Arizona, July 2006, with initiation by joint-controlled rock slope were obtained using multitemporal LiDAR scanning. Topographic changes were detected by comparing historical LiDAR scanning data of this area since 2005 by adopting open-source CloudCompare software. The results showed persistent scour and erosion in the debris flows after 2006. Point cloud data of joint-controlled rock in the initiation zone were generated by the means of photogrammetry using Pix4D software. The joint planes, the dip direction and the dip value of the joint plane, the joint spacing, and the joint roughness were therefore acquired by point cloud processing. Our study contributes a foundation for analyzing the relationship between the rock features, the generation of slope failure, and the initiation of debris flows.

Debris flow behavior during the September 2013 rainstorm event in the Colorado Front Range, USA

Debris flows are highly unpredictable and mechanically chaotic phenomena that can spread or branch away from an expected path or pre-existing channel, a phenomenon termed avulsion. While avulsion is expected to occur over long time periods on mature debris fans, it can also occur on short time scales and outside of active portions of fans. This was the case during the 9–13 September 2013 rainstorm event that triggered over 1000 debris flows in the Colorado Front Range. This research examines the geomorphic and topographic characteristics of debris flows during this event to identify the controlling variables of avulsion during singular events. Avulsion was observed in 1/3 of the debris flows, which were classified into 5 distinct behaviors and thus hazard implications, including directional change, distributary, split, free spreading, and braided. Debris flows that avulsed were twice as long and 6 times more likely to have path obstructions than non-avulsed paths. Additionally, locations along a debris-flow path with low lateral confinement and decreasing slope angles were more prone to avulsion. The high frequency of avulsed debris flows during the 2013 rainstorm event emphasizes the importance of considering avulsion potential during debris-flow mitigation design. The common characteristics of avulsed flows highlighted here could be incorporated into future hazard modeling efforts.

A Study on the Flow Characteristics of Debris Flow Using Small-scaled Laboratory Test

A Study on the Flow Characteristics of Debris Flow Using Small-scaled Laboratory Test

Characteristics and risk analysis of debris flow movement in a strong earthquake area - Sichuan earthquake stricken area as an example

It is very likely that debris flow will break out in a strong earthquake area under the stimulation of a large-scale rainfall, and its risk needs to be analysed. This study analysed the debris flow in a single gully in Wenchuan, introduced the natural environment, geological conditions, and travel conditions and movement characteristics of debris flow in Wenchuan, and then analysed the risk of debris flow using two methods. It was found from the results of a risk calculation based on evaluation factors that the risk of the study area was 0.76, which was high. It was found from the results of a risk calculation based on intensity that the debris flow in the study area had XL level risk, which needed long-term control and monitoring. The research results verify the high risk of debris flow in a strong earthquake area and provide some theoretical bases for debris flow control in that area.

Gradation and Rheological Characteristics of Glacial Debris Flow along the Kangding–Linzhi Section of Sichuan–Tibet Railway

To date, most research on the characteristics of glacial debris flow along the Sichuan–Tibet railway has focused on numerical simulations and remote sensing, resulting in a lack of direct experimental data from debris flow samples. Therefore, in the present study, a field investigation was conducted along the Sichuan–Tibet railway, and 55 samples of glacial debris flow deposits were systematically analyzed to determine their grading and rheological properties. This is the first systematic experimental study on glacial debris flow deposits. The results showed that the proportion of coarse particles was high and the proportion of fine particles was low in the glacial debris flow along the Sichuan–Tibet railway. The average gravel and sand contents were 37.8% and 58%, respectively, and the average contents of silt and clay were 3.7% and 0.47%, respectively. The average fractal dimension was 2.1507, which is much greater than that of viscous debris flow. Under the same gravity and shear rate, the stress of typical glacial debris flow was significantly less than that of viscous debris flow, whereas the variability of the stress was more significant. These findings will contribute to revealing the movement rules and disaster risk of glacier debris flow along the Sichuan–Tibet railway and have considerable theoretical and practical significance for ensuring safety during both its construction and later operation.

The Effects of Particle Segregation on Debris Flow Fluidity Over a Rigid Bed

ABSTRACTIt is essential to consider the fluidity of a debris flow front when calculating its impact. Here we flume-tested mono-granular and bi-granular debris flows and compared the results to those of numerical simulations. We used sand particles with diameters of 0.29 and 0.14 cm at two mixing ratios of 1:1 and 3:7. Particle segregation was recorded with a high-speed video camera. We evaluated the fronts of debris flows at 0.5-second intervals. Then we numerically simulated one-dimensional debris flows under the same conditions and used the mean particle diameter when simulating mixed-diameter flows. For the mono-granular debris flows, the experimental and simulated results showed good agreement in terms of flow depth, front velocity, and flux. However, for the bi-granular debris flows, the simulated flow depth was less, and both the front velocity and flux were greater than those found experimentally. These differences may be attributable to the fact that the dominant shear stress was caused by the concentration of smaller sediment particles in the lower flow layers; such inverse gradations were detected in the debris flow bodies. Under these conditions, most shear stress is supported by smaller particles in the lower layers; the debris flow characteristics become similar to those of mono-granular flows, in contrast to the numerical simulation, which incorporated particle segregation with gradually decreasing mean diameter from the front to the flow body. Consequently, the calculated front velocities were underestimated; particle segregation at the front of the bi-granular debris flows did not affect fluidity either initially or over time.

Characteristics and risk analysis of debris flow movement in strong earthquake area-taking Sichuan earthquake stricken area as an example

It is very likely that debris flow will break out in a strong earthquake area under the stimulation of a large-scale rainfall, and its risk needs to be analysed. This study analysed the debris flow in a single gully in Wenchuan, introduced the natural environment, geological conditions, and travel conditions and movement characteristics of debris flow in Wenchuan, and then analysed the risk of debris flow using two methods. It was found from the results of a risk calculation based on evaluation factors that the risk of the study area was 0.76, which was high. It was found from the results of a risk calculation based on intensity that the debris flow in the study area had XL level risk, which needed long-term control and monitoring. The research results verify the high risk of debris flow in a strong earthquake area and provide some theoretical bases for debris flow control in that area.

Debris flow characteristics and sabo dam function in urban steep slopes

Debris flow characteristics and sabo dam function in urban steep slopes

Assessment of Building Vulnerability with Varying Distances from Outlet Considering Impact Force of Debris Flow and Building Resistance

Studies have been conducted to understand the physical characteristics of debris flows and quantitatively assess the vulnerability of the buildings nearby to mitigate damage from debris flow disasters. However, there remains a paucity of research on vulnerability assessments that discuss the impact force of debris flow and building resistance within certain sections, where debris flows spread from an outlet. In this regard, the study assesses the vulnerability of buildings to debris flows while considering the distance from an outlet. For this purpose, it selects the two sites of Chuncheon-shi in Gangwon-do and Cheongju-shi in Chungcheongbuk-do in South Korea, which are widely known for having experienced debris flow damage in 2011 and 2017, respectively. For the sites, the study conducts an inverse analysis through debris flow simulation to understand the physical characteristics of debris flows, including flow depth, flow velocity, and impact force. Then, the study assesses vulnerability by estimating the resistance of the materials of the buildings placed in the range where debris flows spread, which allows the calculation of a vulnerability index that a building material may have and the estimation of a safety distance from the outlet for each material of the buildings in the study sites. The result shows that with an increasing distance from the outlet, the flow depth, velocity, and impact force, which represent debris flow properties, tend to decrease. This again results in vulnerability being gradually reduced. The study also suggests that buildings are exposed to the risk of debris flow disasters at a sections 40 to 60 m from an outlet for wood material construction, 70 to 110 m for brick-masonry material construction, and all sections from an outlet for prefabricated material construction. Based on this result, the vulnerability index is estimated for the wood material (0.85), brick-masonry material (0.58), and prefabricated material (0.003).

Mobility characteristics of debris slides and flows triggered by Hurricane Maria in Puerto Rico

Mobility is an important element of landslide hazard and risk assessments yet has been seldom studied for shallow landslides and debris flows in tropical environments. In September 2017, Hurricane Maria triggered > 70,000 landslides across Puerto Rico. Using aerial imagery and a lidar digital elevation model (DEM), we mapped and characterized the mobility of debris slides and flows in four different geologic materials: (1) mudstone, siltstone, and sandstone; (2) submarine basalt and chert; (3) marine volcaniclastics; and (4) granodiorite. We used the ratio of landslide-fall height (H) to travel length (L), H/L, to assess the mobility of landslides in each material. Additionally, we differentiated between landslides with single and multiple source areas and landslides that either did or did not enter drainages. Overall, extreme rainfall contributed to the mobility of landslides during Hurricane Maria, and our results showed that the mobility of debris slides and flows in Puerto Rico increased linearly as a function of the number of source areas that coalesced. Additionally, landslides that entered drainages were more mobile than those that did not. We found that landslides in soils developed on marine volcaniclastics were the most mobile and landslides in soils on submarine basalt and chert were the least mobile. While landslides were generally small (< 100 m2) and displayed a wide range of H/L values (0.1–2), coalescence increased the mobility of landslides that transitioned to debris flows. The high but variable mobility of landslides that occurred during Hurricane Maria and the associated hazards highlight the importance of characterizing and understanding the factors influencing landslide mobility in Puerto Rico and other tropical environments.

Experimental study of debris-flow entrainment over stepped-gradient beds incorporating bed sediment porosity

The incorporation of bed sediment by a natural debris flow can cause significant growth in its size and destructive potential. In this study, the erosion features of debris flows in channels with stepped-gradient beds were determined based on field observations and flume experiments. Field investigations revealed that channel sections with abrupt bed slope variations were eroded more intensely than others. A series of small-scale flume tests were conducted to study the pore pressure variations in erodible bed sediment and the basal entrainment behaviour of debris flows in channels with stepped-gradients. Reference tests on a uniform bed slope demonstrate that inflection points in the bed longitudinal profile greatly alter the debris mixture flow pattern and accelerate entrainment. Pore pressure generation in the bed sediment supports debris flow entrainment by reducing basal friction. Peak pore pressures at concave sites were approximately two times higher than those observed at convex sites, likely due to large changes in debris flow dynamics and intense interactions between the flow mixture and bed sediment. Low bed sediment porosities will increase the interlocking of grain particles, promote the formation of clusters and enhance the strength of the grain skeleton, suppressing basal entrainment. In the flume tests, lower peak pore pressures were observed as bed porosity decreased, possibly due to fewer connecting channels for pore fluid pressure to transmit in the compacted bed sediment. Dimensionless analysis indicates that pore pressure fluctuations in the bed sediment were mainly generated by the overriding debris flow. A new entrainment formula of debris flow over stepped-gradient beds is proposed based on flume tests and theoretical analyses, which may aid future debris flow modelling and hazard assessments.

A hydrology-process based method for correlating debris flow density to rainfall parameters and its application on debris flow prediction

Antecedent effective rainfall (Ar) and rainfall intensity (I) play an important role in the formation process of debris flow. Establishing Ar-I threshold curve of debris flow is hence of great importance for early warning purpose. However, conventional statistical models require sufficient observation data, which is not feasible for developing countries without adequate field observation stations. To this end, a hydrology-process based method is proposed to construct the Ar-I threshold. In this model, debris flow is considered as a soil-water mixture composed of solid and water, the loose solid sources contributing to debris flow is provided by the rainfall-induced shallow landslide, and the water is from rainfall-induced runoff. A necessity of having the characteristics of debris flow is that the density of water-soil mixture should approximate to the density of debris flow ranging from 1.2 to 2.3 g/cm3. The value of 1.2 and 2.3 g/cm3, which represent lower and upper borders of the density of debris flow, is used as the threshold for predicting debris flow. The task of the model is to find out the rainfall parameters that correlate with the border value of density and use the searched data of rainfall parameters to fit corresponding curves. Verification of the proposed threshold was conducted based on field observation data of Jiangjia Gully located in Yunnan Province, China, which indicates the false negative and false positive rates of the threshold are 26.7% and 15%, respectively. The precision of the threshold is evaluated as 82.6% by the Receiver Operator Characteristics method, which can provide a solution for debris flow early warning.

Classification and susceptibility assessment of debris flow based on a semi-quantitative method combination of the fuzzy &amp;lt;i&amp;gt;C&amp;lt;/i&amp;gt;-means algorithm, factor analysis and efficacy coefficient

Abstract. The existence of debris flows not only destroys the facilities but also seriously threatens human lives, especially in scenic areas. Therefore, the classification and susceptibility analysis of debris flow are particularly important. In this paper, 21 debris flow catchments located in Huangsongyu Township, Pinggu District, Beijing, China, were investigated. Besides field investigation, a geographic information system, a global positioning system and remote-sensing technology were applied to determine the characteristics of debris flows. This article introduced a clustering validity index to determine the clustering number, and the fuzzy C-means algorithm and factor analysis method were combined to classify 21 debris flow catchments in the study area. The results were divided into four types: debris flow closely related to scale–topography–human activity, topography–human activity–matter source, scale–matter source–geology and topography–scale–matter source–human activity. Nine major factors screened from the classification result were selected for susceptibility analysis, using both the efficacy coefficient method and the combination weighting. Susceptibility results showed that the susceptibility levels of 2 debris flow catchments were high, 6 were moderate and 13 were low. The assessment results were consistent with the field investigation. Finally, a comprehensive assessment including classification and susceptibility evaluation of debris flow was obtained, which was useful for risk mitigation and land use planning in the study area and provided a reference for the research on related issues in other areas.

Sensitivity analysis of influencing parameters on slit-type barrier performance against debris flow using 3D-based numerical approach

Extreme rainfall-induced debris flow can be catastrophic to an urban area, and installation of slit-type barriers can prevent such damage while minimizing negative impact on environments. However, the performance of slit-type barriers against debris flows remains poorly identified partly due to the innate complexity in interactions between debris flow and solid structure. This paper investigated the flow behaviors of debris affected by slit-type barriers using the computational fluid dynamics (CFD) method, in which the numerical model based on the volume of fluid method was verified using the physical modeling results. The sensitivity analysis was performed by building metamodels to determine the primary parameters influencing the barrier performance against debris flows among various variables, in which the effect of input properties and design parameters, particularly the soil concentration in fluidized debris, initial velocity and volume of debris, the barrier height, and the opening ratio, was evaluated from the perspectives of the flow energy reduction and debris trapping. The initial velocity and volume of debris were found to play a significant role in determining the debris flow characteristics. A decrease in the opening ratio in the channel primarily facilitated the energy reduction and trapping due to the reduced opening size. However, the barrier height exhibited a limited effect when the height was sufficiently high to block the debris flow volume. In addition, it was observed that the double barrier system effectively increased the energy reduction while keeping the benefit of open-type barrier. The developed simulation method and obtained results provide an effective tool and an insight that can contribute to an optimum design of the debris-flow barrier.

Significance of coarse clasts in viscous debris flows

Debris flows are flowing mixture of water and sediments (from clay to boulder-sized particles). The sediments control both occurrence and characteristics of debris flows, however, the relevant literature has concentrated mainly on fine debris. Considering their large fractions in debris flows, the significance of coarse clasts (≥0.005 mm) is investigated by comparing the crude debris (CD, the fractions of <10 mm and <5 mm of the Jiangjia Gully debris-flow deposit) with the reconstituted debris (RD, prepared by replacing the coarse clasts of the CD with the corresponding sizes of the Dongyuege debris-flow clasts following the gradation of the CD). Rheometrical tests, propagation tests, and pore-pressure measurements are made on the CD and RD samples in a systematic manner.Aggregation of data collected in 39 tested debris-water mixtures leads us to conclude that the coarse clasts can greatly affect the slurrying susceptibility of debris masses and bulk behavior of slurries. The debris-flow indices (Id) from the CD to RD slurries with maximum grain sizes of 10 and 5 mm decrease by 29% and 17%, respectively. The CD slurries possess higher yield strength and viscosity than their RD counterparts with the same solid volumetric concentrations (Cvs). The areas inundated by 10 CD slurries with maximum grain sizes of 10 and 5 mm are approximately 17%–39% of those of their RD counterparts. The excess pore pressures in the RD slurries dissipate more quickly than those in the CD slurries. The shape and surface texture of coarse clasts regulate slurrying of debris masses, as well as influence their liquefaction potential, which in turn has an impact on the mobility and persistence of subsequent slurries.The platy/flaky debris-producing mountain catchments generally experience lower-magnitude/higher-frequency, lower Cv debris flows of relatively less destructive power, and the debris flows dominated by equidimensional clasts are often more powerful and hazardous, despite their potentially lower frequency.