Debris Flow Sites Research Articles

Assessing the informativeness of a coupled surface–subsurface watershed model for understanding debris flow: a hydrological perspective

ABSTRACT Characterization of debris flow is critical to both risk assessment and hazard mitigation. Recent technologies enable onsite environmental monitoring sensors for geological disaster monitoring. However, the spatiotemporal understanding of debris flow in remote mountainous areas is still limited due to difficulties in observation networks and its complex driving conditions. Here we apply a coupled surface–subsurface hydrological model to examine the characteristics of the water movements near debris flow sites in southwest China. Our approach captured the temporal dynamics of infiltration, redistribution of soil moisture, groundwater storage, and lateral groundwater fluxes. The lateral groundwater flux and groundwater storage were informative indicators in identifying debris flow location. Such informativeness was only effective when hourly dynamics were analysed. Our findings provide new insight into quantifying debris flow susceptibility. This study suggests that the coupled surface–subsurface watershed modelling approach can be informative for preliminary monitoring, planning and management of debris flow.

Analyzing Debris Flow: Topographical Data and Discharge Rate Study

This study used an unmanned aerial vehicle (UAV) for aerial photogrammetry at the Seonseri debris flow site in Gokseong-gun, triggered by heavy rainfall in August 2020. Survey data facilitated the generation of orthographic images and high-resolution digital surface mode (DSM). Finite difference method (FDM) numerical analysis simulated debris flow, exploring the impact of discharge rate and topographic data among input variables. Applying the rational formula for determining debris flow discharge rate emphasized the significance of maximum rainfall intensity just before the event, with high estimated values for runoff coefficient and soil concentration. The study highlighted significant variations in debris flow simulation results based on topographical data accuracy, emphasizing the crucial role of precise site-specific topographical data.

A novel approach for quantifying similarities between different debris flow sites using field investigations and numerical modelling

AbstractDebris flows are geomorphological processes that affect the landscape evolution process of any region. In this study, an integrated methodology is proposed to identify the chance of further debris flows and quantify the similarities between debris flow locations, materials and rheology, using field and laboratory investigations and remote sensing data. The method was tested for four failure‐triggered debris flow sites in the Western Ghats of India, using dimensionless parametric similarity values ranging from 0 to 1. The maximum parametric similarity was observed as 0.84 when comparing the flow accumulation values of Sites 3 and 4, and the maximum overall site similarity was 0.68. The calibrated rheological parameters of one site were found to be satisfactory in modelling the shape of debris flow at all other sites. The findings can be used to identify similar hotspots in the region and to simulate debris flows for quantitative hazard assessment.

Categorization of Debris Flow And Its Prediction along The Highway Roadside of Duhok- Shekhan

Debris flow is caused by various triggers including intensive rainfall, snowmelt, and earthquakes. Quantifying the number, area, and volume of debris is critical to determine debris volume and its risks. Soil physical analysis in conjunction with laboratory geotechnical soil properties of some selected site along the highway roadsides of Duhok-Shekhan assisted in developing empirical models to predict debris flows volume from some input parameters like area, vegetation cover percent, and, the site slope. The debris flow volume was based on measuring (the length, width, and depth) of the individual debris flow sites. The results indicated that debris flows were significantly correlated with debris flow area. In contrast, it was poorly correlated with each of the vegetation cover percentages and site slope; Furthermore, it was shown that the debris flow can be predicted with reasonable accuracy at this stage of study by an exponential model based on debris flow area only. This will enable the responsible agents to take measures to mitigate the risk of a debris flow along the highway roadsides in the study area

Debris-Flow Susceptibility Assessment in China: A Comparison between Traditional Statistical and Machine Learning Methods

Debris flows, triggered by dual interferences extrinsically and intrinsically, have been widespread in China. The debris-flow susceptibility (DFS) assessment is acknowledged as the benchmark for the mitigation and prevention of debris flow risks, but DFS assessments at the national level are lacking. The role of human activities in the DFS assessment has always been overlooked. On the basis of a detailed inventory of debris-flow sites and a large set of environmental and human-related characteristics, this research presents the comparative performance of the well-known information value (IV), logistic regression (LR) and random forest (RF) models for DFS assessments in China. Twelve causative factors, namely, elevation, slope, aspect, rainfall, the normalized difference vegetation index (NDVI), land use, landform, geology, distance to faults, density of villages, distance to rivers and distance to roads, were considered. Debris-flow susceptibility maps were then generated after the nonlinear relationship between the debris-flow occurrence and the causative factors was captured. Finally, the predictive performance of the three maps was evaluated through receiver operating characteristic (ROC) curves, and the validation results showed that areas under the ROC curves were 81.98%, 79.96% and 97.38% for the IV, LR and RF models, respectively, indicating that the RF model outperformed the other two traditional statistical methods. The importance ranking of the RF model also revealed that distance to roads, slope and rainfall dominated the spatial distribution of debris flows. This is the first experiment to compare between the traditional statistical and machine learning methods in DFS studies for the whole of China. Our results could provide some empirical support for China’s policymakers and local practitioners in their efforts to enable residents to be less vulnerable to disasters.

Mitigation measures of debris flow and landslide risk carried out in two mountain areas of North-Eastern Italy

The design of remediation works for the mitigation and prevention of the associated risk is needed where these geological hazards affect anthropized areas. Remedial measures for landslides commonly include slope reshaping, plumbing, drainage, retaining structures and internal slope reinforcement, while debris flow control works consist in open or closed control structures. The effectiveness of the remedial works implemented must be assessed by evaluating the reduction of the risk over time. The choice of the most appropriate and cost-effective intervention must consider the type of hazard and environmental issues, and selects, wherever possible, naturalistic engineering operations that are consequently implemented according to the environmental regulations or the design and specification standards imposed by the competent public administrations. The mitigation procedures consist of five basic steps: (a) acquisition of the knowledge of the hazard process; (b) risk assessment with identification of possible disaster scenarios; (c) planning and designing of specific remedial measures to reduce and/or eliminate the potential risk; (d) slope monitoring after application of remedial measures, (e) transfer of knowledge to the stakeholders. This paper presents two case studies describing the practice for the design of the mitigation measures adopted for debris flow and active landslide sites in North-Eastern Italy. The first case study is a debris flow site, for which, based on observation of past events and numerical simulations using the software FLOW-2D, the most suitable mitigation measures were found to be the construction of a debris basin, barriers and breakers. The second case study deals with an active landslide threatening a village. Based on the landslide kinematics and the results of numerical simulations performed with the code FLAC, hard engineering remedial works were planned to reduce the driving forces with benching and by increasing the available resisting forces using jet grout piles and deep drainage.

Fiber Bragg Grating–Based Flume Test to Study the Initiation of Landslide-Debris Flows Induced by Concentrated Runoff

Abstract In order to explore the initiation of landslide-debris flow caused by concentrated runoff, a flume test has been performed on soil samples taken from a debris flow site in Wenchuan earthquake area. The fiber Bragg grating (FBG) technology was used to measure the strain distribution information in the slope mass during erosion. Several hydrological sensors for monitoring pore water pressure and soil moisture were used to investigate their correlation with internal strain field. The test results show that the fiber optic sensing technique exhibited high sensitivity and precision in monitoring the slope deformation. The development of pore water pressures and soil moistures showed reasonable consistency with the dynamics of an infiltration. According to the strain measurements, there were four evolution stages during the initiation of landslide-debris induced by runoff, i.e., the water absorption stage, the deformation stage, the shear zone formation stage, and the fluidization stage. The results provide an improved insight into the mechanism of debris flow initiation and indicate the enormous potential of the FBG sensing technology in establishing an effective early warning system for landslides and debris flows.

BARSEM DEBRIS FLOW DISASTER IN THE PAMIRS IN 2015 AND ITS ANALOGUES IN THE CENTRAL CAUCASUS

we characterize specific features of formation and consequences of the debris flow disaster occurred on the Barsemdara River in the Gunt River valley (Barsem village, Gorno-Badakhshan Autonomous Region, Tajikistan) on July 16–24, 2015. The paper presents the data on debris flow events with similar formation mechanism that took place in the following river valleys: Adyr-Su in 1940, 1983 and 2011, Tyutyun-Su in 1953, Khaznidon in 1975 et al. A common feature of the considered debris flows is the confinedness of debris flow site to special glacial accumulation forms — moraine pedestals containing a large amount of buried ice. Due to large-scale and long-term debris flow processes moraine pedestals take the shape of gullies. The largest example of considered landform is the debris flow gully (1 km-length) situated in the upper reaches of the Tyutyun-Su River in the Cherek Balkarskiy River basin (Central Caucasus). Similar debris flow processes were also observed in other mountain areas (Zaas River valley (Switzerland) in 1987, valley of the Ishkoman River left tributary (Pakistan) in 2018). Volumes of debris flow material carried out from moraine pedestals reach 1–5 million m3. In 2015 part of the Barsem village territory became covered with debris flow deposits and a dam was formed on the Gunt River above which is the Barsemkul dammed lake now. Places of possible debris flows such as Barsem disasters can be determined on the basis of glacial accumulation form analysis and identification of moraine pedestals in which the debris flow incisions are not yet developed.

Application of Elastic Wave Velocity for Estimation of Soil Depth

Because soil depth is a crucial factor for predicting the stability at landslide and debris flow sites, various techniques have been developed to determine soil depth. The objective of this study is to suggest the graphical bilinear method to estimate soil depth through seismic wave velocity. Seismic wave velocity rapidly changes at the interface of two different layers due to the change in material type, packing type, and contact force of particles and thus, it is possible to pick the soil depth based on seismic wave velocity. An area, which is susceptible to debris flow, was selected, and an aerial survey was performed to obtain a topographic map and digital elevation model. In addition, a seismic survey and a dynamic cone penetration test were performed in this study. The comparison between the soil depth based on dynamic cone tests and the graphical bilinear method shows good agreement, indicating that the newly suggested soil depth estimating method may be usefully applied to predict soil depth.

Assessing the effect of a major storm on 10BE concentrations and inferred basin-averaged denudation rates

Abstract 10Be concentrations in stream sediments are commonly employed to calculate basin-averaged denudation rates. Such calculations assume that denudation is steady in time and that quartz is uniformly distributed in the watershed. The 10Be concentrations in stream sediments are assumed to represent a spatially and temporally averaged concentration, and therefore should not be affected by a discrete erosion event. The effect of such events on 10Be concentrations has been modeled, but has not been previously field-tested following a large precipitation event. In this study, we resampled stream sediments that had been previously analyzed to deduce basin averaged erosion rates in small, tributary basins in the Colorado Front Range following an extreme precipitation event in 2013. Most of our sample sites show no significant change between pre- and post-flood concentrations, and hence no change in the denudation rates inferred from them. The sample locations include a partially burned site, a debris flow site, and sites with very small drainage areas. A notable exception exists at lower Gordon Gulch, within the Boulder Creek Critical Zone Observatory; here, local 10Be data indicate that a large portion of flood-deposited sediment is likely derived from deep soils in fans, terraces, and fills, that are predominantly located on the north-facing toe slope. Overall, the reproducibility of denudation rates deduced from pre- and post-storm samples indicates that the uncertainty associated with 10Be-derived denudation rates is likely less than 15% in this setting.

A Strategic Approach to Debris Flow Risk Reduction on the Road Network

Rainfall-induced debris flows frequently cause disruption to the Scottish road network. A regional assessment of debris flow hazard and risk allows risk reduction actions to be targeted effectively. To this end a strategic approach to landslide risk reduction, which incorporates a classification scheme for landslide management and mitigation has been developed, in order to provide a common lexicon (or group of words) that can be used to describe goals, outcomes, approaches and processes related to risk reduction, and to allow a clear focus on those goals, outcomes and approaches. The focus is thus first on the desired outcome from risk reduction: whether the exposure, or vulnerability, of the at-risk infrastructure and people (and their associated socio-economic activities, which may be impacted over significant areas) is to be targeted for reduction or whether the hazard itself is to be reduced (either directly or by affecting the physical elements at risk). This paper describes the strategic approach in the context of perhaps Scotland's most active debris flow site, the Rest and be Thankful on the A83 strategic road.

Characteristics of debris flows from the lower part of the Lotru River basin (South Carpathians, Romania)

This paper focuses on characteristics of debris flows from the lower part of the Lotru River basin (South Carpathians, Romania). The damage produced by these debris flows has included burial of agricultural land, roads covered by debris flows, and even the obstruction of the Lotru River. Simple statistical analysis has been used to emphasize the characteristics of the debris flow sites. The collected data show that heavy rainfall is the main triggering mechanism of debris flow events in the Lotru hydrographic basin. The daily rainfall data for this region show that important debris flow events generally occur when rainfall exceeds 40 mm in 24 h, while rainfall levels between 25 and 40 mm in 24 h result in hyperconcentrated flows. For 11 of 14 studied debris flow sites, the fan area is greater than the source area, probably due to the thickness of the regolith, which is up to 5–10 m deep. Both source area and deposition area are very dynamic. The retreat rate calculated for five debris flow sites ranges from 5 to 30 m in 30 years (from 1975 to 2005). Channel cross section measurements on one of the debris flows show that velocity values vary from 1.31 to 2.64 m/s; corresponding discharge values vary from 4 to 10.03 m3/s.

DB구축을 통한 강원지역 토석류 유형 분석

최근 우리나라에서는 2002년 태풍 루사, 2003년 태풍 매미, 2006년 태풍 에위니아와 집중호우로 인하여 산지가 약 90%를 차지하고 있는 강원지역의 주택, 도로, 농지가 큰 피해를 입었다. 이로 인한 경제적 손실과 사망자의 대부분은 홍수와 토석류가 발생된 산지 계곡부와 시내에 집중되었다. 본 연구에서는 기존에 강원지역에서 발생된 토석류 발생지에 대한 현장조사를 실시하여 총 180개소의 토석류에 대한 데이터베이스를 구축하였다. 구축된 자료에 대한 분석결과, 강원지역에서 발생된 토석류는 대부분 소규모 사면파괴로부터 시작하였으며, <TEX>$34.3^{\circ}$</TEX>의 비교적 가파른 경사에서 발생하여 평균 <TEX>$18.1^{\circ}$</TEX> 정도의 완만한 경사를 따라 420 m 정도의 비교적 짧은 거리를 이동하는 것으로 나타났다. 또한, 토석류 발생 당일의 강우도 중요하지만 발생 이전의 장기강우가 토석류 발생과 밀접한 관련이 있는 것으로 나타났다. In recent years in Korea, Typhoon Rusa (2002), Typhoon Maemi (2003), and the localized extreme rainfall followed by Typhoon Ewiniar in 2006 devastated residential areas, roads, and agricultural lands in Gangwon province where 90% of the area is in mountainous regions. Most of the economic losses and casualties were concentrated in the area near the mountain valleys and creeks due to the floods and debris flows. In this study, DATABASE, which includes a total 180 debris flow events in the Gangwon area, was created by collecting the hazard records and field investigations of existing debris flow sites. Analysis results showed that the most of the debris flows in Gangwon province initiated from the small slope failure with relatively steep slope of <TEX>$18.1^{\circ}$</TEX>. And they flowed short distances about 420 m in gentle slope with the average angle of <TEX>$18.1^{\circ}$</TEX>. In addition, rainfall condition was important for the triggering of debris flow not only at the day of debris flow but also extended period of rainfall before debris flow.

항공 라이다 자료를 이용한 토석류 발생지역의 지형복원기법 개발

항공 LiDAR 측량으로 토석류 발생 전 후의 지형자료를 취득하는 경우 토석류로 인하여 유출된 토사량을 알 수 있다. 그러나 토석류 발생지를 미리 예측하여 촬영하기가 힘들고, 토석류 발생 지역의 과거 항공 LiDAR 자료는 존재가능성이 낮아 토석류 발생이전 지형자료를 이용하는 것은 어렵다. 따라서 본 연구에서는 토석류 발생지역의 토사량 추정을 위해 발생전 지형을 복원하고, 토사유출의 공간적 범위를 파악할 수 있는 지형복원기법을 개발하였다. 지형복원기법은 토석류 발생지역에서 추출한 선형 및 비선형 횡단면을 가우시안혼합모델로 수식화하고 중심점 추정방법과 근사정확도로 근사결과를 평가하여 토석류 발생이전의 지형을 복원한다. 지형복원기법은 토석류 발생 전 후의 항공 LiDAR 자료를 이용하여 두 가지 방법으로 검증하였다. 먼저 토석류 발생구간에서 추출한 각 횡단면을 지형복원하여 발생전 항공 LiDAR 자료와 비교하였다. 또한 토석류 발생지역에 지형복원기법을 적용한 뒤 지형자료를 제작하여 토석류 발생전 항공 LiDAR DEM과 비교하여 검증하였다. 지형복원기법의 검증한 결과 전반적으로 근사정확도가 0.5m에 가까운 높은 정확도를 나타냈다. The flowed soil is able to be estimated from topographic data of before and after the debris flow. However, it is often difficult to obtain airborne LiDAR data before the debris flow area. Thus, this study tries to develop a topographic restoration method that can provide spatial distribution of flowed soil and reconstruct the topography before the debris flow using airborne LiDAR data. The topographic restoration method can express a numerical formula induced from a Gaussian mixture model after extracting the cross sections of linear or non-linear in debris flowed area. The topographic restoration method was verified by two ways using airborne LiDAR data of before and after the debris flow. First, each cross section extracted from the debris flow sites to restore the topography was compared with airborne LiDAR data of before the debris flow. Also, the topographic data produced after the topographic restoration method applied to the debris flow sites was verified by airborne LiDAR DEM. Verifying the results of the topographic restoration method, overall fitting accuracy showed high accuracy close to 0.5m.

A characterisation of the physical properties of soil and the implications for landslide occurrence on the slopes of Mount Elgon, Eastern Uganda

Soil properties of major landslides that occurred recently on the mid-altitude slopes of Mount Elgon, eastern Uganda were analysed. A mudflow, located at the Kitati protected forest site, and two deep debris flows on the Nametsi and Buwabwala deforested steep slopes (36°–58°) were surveyed. In order to test the hypothesis that ‘soils at the landslide sites are particularly ‘problem soils’ and thus prone to landslides’, the following analyses were undertaken: particle size distribution, Atterberg limits, shear strength and factor of safety (Fs). Soils at the Kitati and Buwabwala sites exhibited expansive potential, owing to clay contents well above 20%. A clay content exceeding 32% was identified at the Nametsi debris flow site implying an extremely high expansive potential of the soil. High liquid limits (LLs) at Kitati (59%) and Buwabwala (53%) meant that the soils qualified as vertisols susceptible to landslides. High plasticity indices (PIs) (averaging 33%) also confirmed the vertic nature of soils at the Nametsi debris flow site. Whereas the value of Fs 1). Despite this finding, the stable sites could be described as only conditionally stable because of the interplay of various physical, pedological and anthropogenic factors. The results point to the fact that soils at the landslide sites are inherently ‘problem soils’ where slope failure can occur even without human intervention. Therefore, the hypothesis that soils at three landslide sites are inherently ‘problem soils’ and prone to landslides, is accepted.

Biological and water quality responses to hydrologic disturbances in third‐order forested streams

AbstractWe compared stream ecosystem responses to two types of disturbances: flood and debris flows. A large storm in February 1996 disturbed four similarly sized sub‐watersheds of the Calapooia River, in the Cascade Mountains of Oregon, USA. All sub‐watersheds had flood and in two, 31 and 81% of the perennial channel, a debris flow affected the channel. For 8 years, we used a suite of approaches: stream temperature, nutrient regime, periphyton and macroinvertebrate assemblages, and resident trout abundance and habitat to evaluate the persistence of instream impacts. Differences in stream temperatures and nitrate‐nitrogen concentrations were evident, probably, due to the removal of vegetation and modification of riparian soils at the debris flow sites. Instream biological responses varied. After the event, fish, including trout, were rare with no fish at the debris flow sites. Within 6 years, trout densities (Oncorhynchus mykiss and Oncorhynchus clarki) were similar and young‐of‐the‐year trouts were common. In contrast, periphyton and macroinvertebrate assemblages differed. Periphyton biomass was lower and nitrogen‐fixing periphyton was more abundant at the debris flow sites. Macroinvertebrate assemblage diversity was higher at the debris flow sites due to fewer dominant taxa. Macroinvertebrate functional feeding groups also differed with fewer gatherers and more scrapers at the debris flow sites. Debris flow impacts related to loss of riparian canopy will probably persist until mature red alder stands are re‐established along stream‐reaches affected by debris flows to provide nitrogen input and shade. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Controls on fan depositional processes in the schist ranges of the Southern Alps, New Zealand, and implications for debris-flow hazard assessment

Sixteen morphometric and vegetation cover variables associated with 32 debris-flow and 28 fluvial fans and their basins in the schist ranges of the Southern Alps of New Zealand are examined. The results show statistically significant differences in the area, length, planimetric shape, relief ratio, Melton's ruggedness ( R), and forest and total vegetation cover between debris-flow and fluvial basins, and in the apex and toe elevations, area, and upper and average axial gradients between debris-flow and fluvial fans. All of these variables except the apex and toe elevations of the fans reflect differences between debris-flow and fluvial processes and environmental controls on them. Discriminant analysis indicates that the relief ratio and Melton's R of the basin and upper and average gradients of the fan axis are able to correctly classify debris-flow and fluvial fans, with almost equally good results obtained by employing only a pair of variables: either basin relief ratio and upper fan gradient or basin Melton's R and basin shape. The lower thresholds at debris-flow sites and upper thresholds at fluvial sites for the relief ratio and Melton's R of the basin and upper and average gradients of the fan are identified, and these as well as the mean values of these variables show significant differences from fans in nearby sedimentary ranges of the Southern Alps with important implications for the assessment of debris-flow hazard on fans. Fan gradient is found to be closely associated with basin size (area and length) at debris-flow sites, but with basin ruggedness (relief ratio) at fluvial sites. Both fan types show a weak association between their size and the size of the contributing basin.

Geologic, geomorphic, and meteorological aspects of debris flows triggered by Hurricanes Frances and Ivan during September 2004 in the Southern Appalachian Mountains of Macon County, North Carolina (southeastern USA)

In September 2004, rain from the remnants of Hurricanes Frances and Ivan triggered at least 155 landslides in the Blue Ridge Mountains of North Carolina. At least 33 debris flows occurred in Macon County, causing 5 deaths, destroying 16 homes, and damaging infrastructure. We mapped debris flows and debris deposits using a light-detecting and ranging digital elevation model, remote imagery and field studies integrated in a geographic information system. Evidence of past debris flows was found at all recent debris flow sites. Orographic rainfall enhancement along topographic escarpments influenced debris flow frequency at higher elevations. A possible trigger for the Wayah and fatal Peeks Creek debris flows was a spiral rain band within Ivan that moved across the area with short duration rainfall rates of 150–230 mm/h. Intersecting bedrock structures in polydeformed metamorphic rock influence the formation of catchments within structural–geomorphic domains where debris flows originate.

Relationships between debris flows and earth surface factors in Southwest China

Southwest China, including the Provinces of Yunnan, Guizhou, Sichuan and Chongqing, is a region with serious debris flow hazards, where 7,561 debris flow sites have been identified. Based on the data from these sites, the distribution regularity of debris flows was analyzed. Earth surface factors that may influence the formation of debris flows were analyzed from the viewpoints of energy and material conditions. Four major earth surface factors were selected: relative relief, stratigraphy, fault density and land-use conditions. With the support of GIS, the research region was divided into 125,177 grid cells and for each cell data for the four factors were collected. Based on this information, the distribution of quantity and the occurrence probability of debris flows and the role of each factor were statistically analyzed. The results should be helpful for the assessment of debris flow hazards and debris flow forecasting in the research region.

A great disastrous debris flow on 11 July 2003 in Shuikazi valley, Danba County, western Sichuan, China

A debris flow burst on July 11, 2003, in Shuikazi valley of Danba County, western Sichuan Province (Fig. 1), which took 51 lives and caused extensive property damage. This disastrous debris flow tops the world in 2003 due to death toll. In this short note, the characteristics of debris flow were introduced and the conflux process was analyzed based on our work. To remedy this, we should know the characteristics of the debris flow very well, and we should analyze its mechanics after the field investigation. There are about ten family houses and some village gardens built in the Qiongshan debris fan near Bade village, 28 km away from Danba County. That night a group of local youngsters sang and danced in honor of four Shanghai tourists in a village garden. But At 23:20 the debris flow burst and arrived at the ravine mouth. Because the loud, happy music weakened the people s sentience to the vibration sound of the oncoming debris flow, almost all the youngsters in that village were swallowed up by the debris flow. This tragedy shocked the local government, and we are invited to explore the debris flow site. It was found that in addition to the causalities, about 73,136 m2 of woodlands, and farmlands were eroded (Fig. 2), and ten houses were damaged or destroyed (Fig. 3). The main stream was blocked for a few minutes, and its bed rose up. This debris flow damaged a 500-m highway and generated some potential hazards. For the occurrence of the debris flow, the “Beauty Valley” was renamed as “Horrible Valley.”