Characteristics Of Debris Flow Research Articles

Analyzing Bulk Flow Characteristics of Debris Flows Using Their High Frequency Seismic Signature

AbstractQuantifying debris‐flow characteristics remains a key challenge in natural hazard research. Recent studies suggest that seismic signals can reveal debris‐flow properties. However, the accuracy and applicability of theoretical models linking bulk flow properties to the seismic signature of a debris flow remain elusive. By extending a previously proposed model of random single‐particle impact forces to multi‐particle force chains acting on the channel bed, we describe the generation of high frequency seismic signals, and thereby estimate the bulk flow dynamics of six debris‐flow events at Illgraben, Switzerland. The theoretically predicted basal force fluctuations agree with in‐situ measurements at a basal force plate and seismic signals recorded adjacent to the channel. According to our model, both random single‐particle impacts and random impacts caused by multi‐particle force chains control basal force fluctuations. The relative contributions of single particles and of multi‐particle force chains may vary significantly for different events and different positions within events. The relative contribution of multi‐particle force chains is expected to be larger in the flow front, where particle concentrations are higher. The ratio between single‐particle and multi‐particle contributions appears to control the non‐linear relation between flow depth and the magnitude of the high frequency seismic signals. Our results suggest that fluctuating basal forces are strongly controlled by particle size and flow depth, and open new perspectives for the understanding of bulk flow characteristics, such as flow depth and weight, and of the high frequency seismic signals generated by debris flows.

A Case Study on the Closed-Type Barrier Effect on Debris Flows at Mt. Woomyeon, Korea in 2011 via a Numerical Approach

Debris flows are capable of flowing with high velocities and causing significant economic and infrastructural damage. As a hazard mitigation measure, physical barriers are frequently installed to dissipate the energy of debris flows. However, there is a lack of understanding on how barriers affect and interact with debris-flow behavior (e.g., velocity and volume). This study investigated the changes in debris-flow characteristics depending on the installation location of barriers. Mt. Woomyeon, which is located in Seoul, Korea, was the site of a major debris-flow event in 2011. This study modeled this event using DAN3D, numerical software based on smoothed particle hydrodynamics (SPH). Our numerical approach assessed changes in debris-flow behavior, including velocity and volume, as the debris flow interacts with four closed-type barriers installed at separate points along the flow path. We used DAN3D to model the barriers via terrain elevation modifications. The presence of a closed-type barrier results in the reduction in the debris-flow velocity and volume compared to when no barrier is present. Most notably, the closer a barrier is installed to the debris source, the greater the velocity decrease. By contrast, a barrier that is constructed further downstream allows the debris flow to undergo entrainment-driven growth before confronting the barrier, resulting in a larger debris deposition volume that can often cause overflow, as shown at our particular study site. The presented results highlight the effectiveness of barriers as a method of hazard mitigation by providing insight into how such installations can alter debris-flow behavior. In addition, the findings can provide a reference for future debris-flow barrier designs, increasing the effectiveness and efficiency of such barrier systems.

Experimental study on the discharge characteristics of viscous debris flow with grid-type dam

Experimental study on the discharge characteristics of viscous debris flow with grid-type dam

Depositional morphology of debris flow in the junction with mainstream channel

Debris flow carries a large amount of sediment into the main river quickly, which causes river-blocking or diversion and leads to considerable losses in alpine regions. The research on the deposition characteristics of debris flow at the confluence with the mainstream channel is significant to understanding the riverbed evolution. However, the deposition mechanisms and morphology of debris flow at the confluence with the mainstream channel are not clear. This paper analyzes 80 debris flow cases at the Minjiang basin confluence in the Wenchuan earthquake area according to this phenomenon. It is found that the frequency of debris flows increases sharply after the earthquake. Moreover, the debris flow has the characteristics of sudden and mass occurrence. The deposition morphology of debris flow is also discussed with satellite images. Compared with the surface debris flow, the depositional fan at the confluence is mainly diffused along the flow direction of the main river and often presents an asymmetric broom shape because of the erosion of the main river. The relationship between the possibility of river-blocking and the properties of debris flows is also discussed. Results reveal that the river-blocking is closely related to the discharge and topography of the confluence. Furthermore, debris flow with high discharge (>200 m3/s), large density (>1.8 t/m3), and high velocity (>10 m3/s) easily trigger river-blocking. On this basis, a dimensionless parameter representing the characteristics of debris flow and mainstream hydrodynamic conditions is established, which can be used to measure the characteristics of regional river-blocking. Thus, the discriminant formula of the runout distance and the deposition morphology of debris flows are obtained. This paper studies the interaction between mainstream and debris flow and provides scientific methods for preventing and treating debris flow.

Early identification and monitoring of hidden debris flow in low mountain red bed area based on InSAR and optical remote sensing technology——A case study of Wenjiagou debris flow in the Eastern New District of Chengdu

Because of the typical geological environment and climate conditions, the number of debris flow geological disasters in low mountain red bed area is small, and most of them have high concealment. Identifying and monitoring debris flow under this kind of special disaster pregnant background has a certain significance for the prevention and control of geological disasters. Taking Wenjiagou debris flow in Danjing street, Eastern New District of Chengdu as an example, this paper uses InSAR technology and optical remote sensing technology to identify and monitor Wenjiagou debris flow by multi-period, multi-source and multi-means method. Combined with the geological environment conditions of red bed area, this paper comprehensively analyzes the causes and development characteristics of Wenjiagou debris flow. Research shows:1) The debris flow in Wenjiagou is very hidden. The source of landslide in the early stage can be detected by using InSAR technology, which has certain deformation characteristics. 2) Using multi- period optical remote sensing images, the partial slope deformation can be identified in the study area, and the debris flow can be effectively identified in the early stage. 3) The provenance of Wenjiagou debris flow is mainly controlled by geological structure and stratum lithology. Finally, combined with the results of remote sensing interpretation and ground survey, the paper puts forward the targeted prevention and control suggestions of “Stable material source + Combination of blocking and drainage + Ecological restoration” for Wenjiagou debris flow, which has a certain guiding role for the development and planning of the Eastern New District of Chengdu.

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.

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.