Debris Flow Disaster Research Articles

Emergency responses to debris flow disaster at Serizawa, Nikko-city triggered by the 2015 torrential rains in the Kanto and Tohoku region

Emergency responses to debris flow disaster at Serizawa, Nikko-city triggered by the 2015 torrential rains in the Kanto and Tohoku region

다중회귀분석을 이용한 토석류 재해 분석의 주요 인자인 연행증가율 추정

최근 지구 온난화에 의한 기후변화와 함께, 우리나라의 집중호우 및 태풍에 의한 토사재해의 강도가 심화되고 있다. 토석류는 산사태에서 발전된 형태로 많은 강수량으로 인해 경사가 급한 산지나 계곡에서 물과 토석이 혼합되어 빠르게 흐르는 현상으로 정의할 수 있다. 토석류로 인한 피해를 방지하기 위해서는 토석류 발생 유무 및 토석류 확산 경로 및 흐름 방향 등을 정량적으로 예측할 필요성이 있다. 이를 정량적으로 고려할 수 있는 다양한 수치 모델이 개발되었으며 이 중 DAN3D로 불리는 모델이 연속체 다이나믹 수치 모델로서 국내의 토석류 거동을 보다 정확히 모사하는 것으로 알려져 있다. DAN3D는 기존 토석류 해석 모델이 고려하지 못하는 토석류의 유하 과정에서의 침식에 의한 연행작용으로 인한 부피증가 현상을 모델에 반영하고 있는데, 문제는 토석류 발생이 예측된 지점에서 연행증가율을 결정할 수 있는 방법이 아직까지 존재하고 있지 않다. 따라서 본 연구에서는 실제 토석류가 발생했던 국내 35개 지점에 대해 토석류 연행작용에 영향을 끼치는 것으로 알려진 13개의 독립변수와 평균 연행증가율에 대한 데이터베이스를 구축하였으며 이를 근거로 다중회귀분석을 수행하여 연행증가율을 제시하였다. 다중회귀분석 결과 모든 통계적 조건들을 충족하였으며 82.4%의 결정계수 값을 나타냈다. Recently, landslide and debris-flow disasters caused by severe rain storms have frequently occurred. Landslides can be mobilized into debris-flows, and then they transport downwards with huge volumes of sediments in an extreme rainfall condition. It is necessary to analyze flow direction and route of debris-flow for the prevention of debris-flow disaster. Many numerical models have been developed to consider these properties of debris-flow, and DAN3D which is a continuum dynamic runout model is known to simulate real events of debris-flow in Korea. DAN3D considers volume increase of various sediments induced by an entrainment mechanism. However, it uses several user-prescribed parameters, and there is no clear method to determine the parameter values. Therefore, this research analyzed 35 previous debris-flow events in Korea and collected values of dependent and independent variables to decide the growth rate. Besides, a multiple regression analysis was conducted and an empirical solution with an <TEX>$R^2$</TEX> value of 0.824 was suggested for the prediction of growth rate. In the solution, all statistical assumptions for the multiple regression analysis were satisfied.

Historical analyses of debris flow disaster occurrences and of their scientific investigation in Brazil

Considering the debris flow as highly-destructive flow of water and sediment mixture in a way where it is a gravity-governed continuous flow, the present paper conducted a Web survey of technical-scientific studies that treated these phenomena which occurred in Brazil during the period 1900-2014. Although the increase of occurrence from the 1990s caused the increase in the number of publication, there are still a small number of publications, especially in scientific journals. A historical analysis about Brazilian studies demonstrates an actual situation in Brazil and confirms various necessary and urgent actions. Among them, the more important actions are: (1) establishment of terminology and concept about debris flow in Brazil; (2) systematization of hydrometeorological monitoring and topographic survey; (3) registration of occurrences and data-base construction; and (4) development of woody debris flow researches.

산사태 위험지도와 연계된 도심지 토사재해 취약성 평가: 부산광역시 적용

In this study, an urban mud and debris flow disaster vulnerability assessment model based on landslide risk map being used by Korea forest service is proposed. In order to examine the vulnerability of urban areas, the assessment model is configured to reflect the exposure intensity, sensitivity level, and the ability to adapt to landslides. The proposed model consists of one zoning and three detailed indicators which are a buffer zone derived by landslide hazard map, an indicator of personal injury, an indicator to cause secondary damage, and an indicator of disaster preparedness and response capability. Three detailed indicators have six, five, and six agencyrelated variables, respectively. The weights among detailed indicators and those among surrogates that make up each detailed indicator are setting by the AHP survey technique. The developed model is applied to Busan, and the vulnerability of urban mud and debris flow disaster is evaluated.

Mobile Healthcare System for Health Checkups and Telemedicine in Post-Disaster Situations.

Portable Healthcare Clinic (PHC) is a mobile healthcare system comprising of medical sensors and health assessment criteria. It has been applied in Bangladesh for the last two years as a pilot program to identify non-communicable diseases. In this study, we adapted PHC to fit post-disaster conditions. The PHC health assessment criteria are redesigned to deal with emergency cases and healthcare worker insufficiency. A new algorithm makes an initial assessment of age, symptoms, and whether the person is seeing a doctor. These changes will make the turn-around time shorter and will enable reaching the most affected patients better. We tested the operability and turn-around time of the adapted system at the debris flow disaster shelters in Hiroshima, Japan. Changing the PHC health assessment criteria and other solutions such as a list of medicine preparation makes the PHC system switch into an emergency mode more smoothly following a natural disaster.

통계 분석을 통한 산사태 토석류 전이규준 모델

최근 들어 집중호우로 인한 산사태 및 토석류 피해가 종종 발생하고 있다. 이에 따라 산사태 재해 예측에 관한 연구 중 산사태 민감도 분석과 토석류 위험도 분석 관련 연구는 활발하게 진행되어 왔지만, 사면 지역에 적용하기 적합한 전이 분석 관련 연구는 부족한 실정이다. 본 연구에서는 판별분석과 로지스틱 회귀 분석과 같은 통계적 방법을 이용하여 실제 토석류가 발생했던 지역에서 추출한 지형학적 인자, 지질학적 인자 등을 토대로 토석류 전이규준을 제시하였다. 10개의 지형학적 및 지질학적 인자가 독립변수로 사용되었으며 실제 466개소(비전이: 228개소, 전이: 238개소)의 토석류 비전이 및 전이 데이터가 수집되었다. 우선, Fisher의 판별 분석이 수행되었으며, 수행 결과 실제경우와 91.6%의 분류 정확도를 보였다. 하지만 전이와 비전이 두 그룹간의 공분산 동질성이 만족되지 않았으며 또한 독립변수들이 정규분포를 보이지도 않았다. 두 번째로 이항 로지스틱 회귀분석이 수행되었으며, 분석 결과 92.3%의 분류 정확도를 나타냈으며 모든 통계적 조건들도 유의하게 나타났다. 따라서 이항 로지스틱 회귀 분석을 이용한 전이 규준은 토석류 재해 발생 여부를 예측하는데 효과적으로 사용될 수 있을 것으로 판단된다. Recently, landslide and debris-flow disasters caused by severe rain storms have frequently occurred. Many researches related to landslide susceptibility analysis and debris-flow hazard analysis have been conducted, but there are not many researches related to mobilization analysis for landslides transforming into debris-flow in slope areas. In this study, statistical analyses such as discriminant analysis and logistic regression analysis were conducted to develop a mobilization criterion using geomorphological and geological factors. Ten parameters of geomorphological and geological factors were used as independent variables, and 466 cases (228 non-mobilization cases and 238 mobilization cases) were investigated for the statistical analyses. First of all, Fisher's discriminant function was used for the mobilization criterion. It showed 91.6 percent in the accuracy of actual mobilization cases, but homogeneity condition of variance and covariance between non-mobilization and mobilization groups was not satisfied, and independent variables did not follow normal distribution, either. Second, binomial logistic analysis was conducted for the mobilization criterion. The result showed 92.3 percent in the accuracy of actual mobilization cases, and all assumptions for the logistic analysis were satisfied. Therefore, it can be concluded that the mobilization criterion for debris-flow using binomial logistic regression analysis can be effectively applied for the prediction of debris-flow hazard analysis.

Lake outburst and debris flow disaster at Kedarnath, June 2013: hydrometeorological triggering and topographic predisposition

Heavy rainfall in June 2013 triggered flash flooding and landslides throughout the Indian Himalayan state of Uttarakhand, killing more than 6000 people. The vast majority of fatalities and destruction resulted directly from a lake outburst and debris flow disaster originating from above the village of Kedarnath on June 16 and 17. Here, we provide a systematic analysis of the contributing factors leading to the Kedarnath disaster, both in terms of hydrometeorological triggering and topographic predisposition. Topographic characteristics of the lake watershed above Kedarnath are compared with other glacial lakes across the north-western Himalayan states of Uttarakhand and Himachal Pradesh, and implications for glacier lake outburst hazard assessment in a changing climate are discussed. Our analysis suggests that the early onset of heavy monsoon rainfall (390 mm, June 10–17) immediately following a 4-week period of unusually rapid snow cover depletion and elevated streamflow was the crucial hydrometeorological factor, resulting in slope saturation and significant run-off into the small seasonal glacial lake. Between mid-May and mid-June 2013, snow-covered area above Kedarnath decreased by around 50 %. The unusual situation of the lake being dammed in a steep, unstable paraglacial environment but fed entirely from snowmelt and rainfall within a fluvial dominated watershed is important in the context of this disaster. A simple scheme enabling large-scale recognition of such an unfavourable topographic setting is introduced. In view of projected 21st century changes in monsoon timing and heavy precipitation in South Asia, more emphasis should be given to potential hydrometeorological triggering of lake outburst and debris flow disasters in the Himalaya.

가능 최대강수량에 의한 토석류 범람 예측

In recent years, debris flow disaster has occurred in multiple locations between high and low mountainous areas simultaneously with a flooding disaster in urban areas caused by heavy and torrential rainfall due to the changing global climate and environment. As a result, these disasters frequently lead to large-scale destruction of infrastructures or individual properties and cause psychological harm or human death. In order to mitigate these disasters more effectively, it is necessary to investigate what causes the damage with an integrated model of both disasters at once. The objectives of this study are to analyze the mechanism of debris flow for real basin, to determine the PMP and run-off discharge due to the DAD analysis, and to estimate the influence range of debris flow for fan area according to the scenario. To analyse the characteristics of debris flow at the real basin, the parameters such as the deposition pattern, deposit thickness, approaching velocity, occurrence of sediment volume and travel length are estimated from DAD analysis. As a results, the peak time precipitation is estimated by 135 mm/hr as torrential rainfall and maximum total amount of rainfall is estimated by 544 mm as typhoon related rainfall.

インドネシア・メラピ山 2010年噴火以降の土石流災害報告

インドネシア・メラピ山 2010年噴火以降の土石流災害報告

Risk Assessment of the Debris Flow Gully in Tibet Southeast

Risk assessment of debris flow is the core content and decision-making basis for debris flow disaster forecasting and the disaster prevention work. It is a comprehensive analysis for the geological, climate, rainfall, historical disaster activities and human engineering activities in some certain areas which may be in danger conditions, so as to determine the occurrence probability of debris flow. In this study, risk assessment model of the debris flow gully in Tibet southeast area is established. According to the correlation ratio of risk assessment indexes and the debris flow occurrence, the assessment indexes can be divided into three levels and defined with some certain values according to the correlation of debris flow occurrence. Finally, the risk assessment of debris flow gully in Tibet southeast area is conducted, and model outputs achieve a good result.

Applying a Method for Assessing Deep-Seated Rapid Landslide Susceptibility in Jember District, East Java Province, Indonesia

A deep-seated rapid (catastrophic) landslide is a phenomenon that may cause serious damage due to the large amount of sediment movement, such as the formation of a landslide dam and debris flows. In Japan, a method for estimating deep-seated rapid (catastrophic) landslide susceptibilities for many small catchments (ca. 1 km2) over relatively large areas (ca. hundreds of km2) was proposed in 2008. In the present study, we applied the Japanese method to the northern part of Jember, East Java, Indonesia, where a debris flow disaster occurred due to the collapse of a landslide dam formed by a deep-seated rapid (catastrophic) landslide in 2004. Although there were several limitations related to data availability, we successfully assessed susceptibility to deep-seated rapid landslides.

Recognition, opinion and evaluation of sabo by the residents around debris flow disaster stricken area in Miyake Island

Recognition, opinion and evaluation of sabo by the residents around debris flow disaster stricken area in Miyake Island

1A1-U04 土石流災害を防ぐための火山表面観測手段の検討

1A1-U04 土石流災害を防ぐための火山表面観測手段の検討

Experimental Study on Dynamic Responses of a New Type of Debris Flow Dam under Solid Impact Load

Dams can effectively alleviate great debris flow hazards to downstream regions, so they has been widely applied to prevention and control engineering of debris flow disaster now. A kind of steel-concrete combined structure with steel braces was presented based on conventional gravity dams, and the superiority of the new structure in terms of impact resistance was verified contrastively by means of model experiments under solid impact. The results show that braces can restrain cracks and reduce their width, thus the extent of damage in impact areas is alleviated effectively. Compared with the conventional dam, the dynamic strains and acceleration peak values of the dam with braces both observably reduce, and the highest reduction ranges of them may be up to 69.2% and 47.8% respectively, so the deformation and vibration are limited by the braces. The dynamic displacement peak values of the new-type dam are significantly less than the conventional dam, and the average reduction range of this index can reach to about 46%, so the structural stiffness has been enhanced by a large margin.

An Approach to the Forecasting of Debris Flow Hazard by Storms from Large Waste-Dump at Open Pit Mines

In order to explore the impact of debris flow in large waste-dump which under the situation of rainstorm could cause disasters to the downstream region of the life and property; the research project has chosen a large waste-dump as the engineering background in Jiuzhaigou, Sichuan. According to the theory of the debris flow motion, we have made a deep analysis about the possibilities that waste-dump could cause debris flow disaster under the different frequency of rainstorm; and carried on the forecast analysis about the scope and degree of the calamity in the downstream which caused by the debris flow. The results can provide a reference for debris flow control in the lower reaches.

Countermeasures and Scheme in Preventing Zhaohe River Debris Flow Disaster in Erlong Town, Zhenping County in Henan Province

Zhaohe debris flow gully is located in the south foothill of Funiu Moutain, serious debris flow disasters occurred here. Now it is still threatening downstream villagers’ life and property safety directly. The geology, landform, climate and other natural environment conditions of Zhaohe valley were analyzed. It shows that Zhao He have debris flow formation conditions. A comprehensive treatment scheme including fending dikes, cleaning river, suppressing foot engineering and biological measures, was put forward based on the hazard characteristic.

Combined impacts of antecedent earthquakes and droughts on disastrous debris flows

This paper describes a study on the combined impacts of antecedent earthquakes and droughts on disastrous debris flows. This is a novel attempt in quantifying such impacts using the effective peak acceleration (EPA) (to represent earthquakes) and standardized precipitation index (SPI) (to represent droughts). The study is based on the analysis of 116 disastrous debris flow events occurred in Mainland China in the last 100 years covering a wide spectrum of climate types and landforms. It has been found that the combined impacts from earthquakes and droughts on disastrous debris flows do exist and vary from low to very high according to different climate conditions and terrains. The impacts from earthquakes increase with the increased terrain relief, and the impacts from droughts are strongest in semi-humid climate condition (with reduced impacts in humid and semi-arid /arid climate conditions). Hypothetical explanations on the study discoveries have been proposed. This study reveals the possible reasons for the disastrous debris flow distributions around the world and has significant implications in paleo-climate-seismic analysis and disastrous debris flow risk management.

A regional-scale method of forecasting debris flow events based on water-soil coupling mechanism

A debris flow forecast model based on a water-soil coupling mechanism that takes the debris-flow watershed as a basic forecast unit was established here for the prediction of disasters at the watershed scale. This was achieved through advances in our understanding of the formation mechanism of debris flow. To expand the applicable spatial scale of this forecasting model, a method of identifying potential debris flow watersheds was used to locate areas vulnerable to debris flow within a forecast region. Using these watersheds as forecasting units and a prediction method based on the water-soil coupling mechanism, a new forecasting method of debris flow at the regional scale was established. In order to test the prediction ability of this new forecasting method, the Sichuan province, China was selected as a study zone and the large-scale debris flow disasters attributable to heavy rainfall in this region on July 9, 2013 were taken as the study case. According to debris flow disaster data on July 9, 2013 which were provided by the geo-environmental monitoring station of Sichuan province, there were 252 watersheds in which debris flow events actually occurred. The current model predicted that 265 watersheds were likely to experience a debris flow event. Among these, 43 towns including 204 debris-flow watersheds were successfully forecasted and 24 towns including 48 watersheds failed. The false prediction rate and failure prediction rate of this forecast model were 23% and 19%, respectively. The results show that this method is more accurate and more applicable than traditional methods.

토석류에 의한 건물의 물리적 취약함수 특성

2011년 7월과 8월 사이에 발생한 총 8개 토석류 재해 지역에 대한 재해이력 사례를 분석하여 각 재해지역의 토석류 물리적 특성을 파악하였다. 또한 각 재해지역에서 피해를 입은 15개 건물에 대한 손상 특성 분석을 수행하였다. 토석류의 물리적 특성과 건물 손상정도를 바탕으로 토석류의 높이, 속도 및 충격압력으로 구성된 취약함수를 구하였다. 또한 보강 콘크리트 구조와 비 콘크리트 구조와 같은 건물의 구조 형식에 따른 취약함수를 각각 산출하였다. 비 콘크리트 건물의 경우 토석류 충격압이 30 kpa 이상일 때 완전 파괴, 15~30 kPa일 때 심각한 손상, 0~15 kPa일 때 경미한 손상이 발생하는 것으로 분석되었다. 이에 비해 보강 콘크리트 건물의 경우 100 kPa 이상에서 심각한 손상, 35~100 kpa일 때 보통 손상, 0~35 kPa일 때 경미한 손상을 입는 것으로 파악되었다. 콘크리트 건물의 경미한 손상에 대응하는 토석류 충격압은 비 콘크리트 건물에서는 완전 파괴에 해당되는 손상을 가져다 줄 수 있음을 의미한다. 건물 구조형식과 토석류 물리적 특성에 따른 취약곡선을 비선형 회귀분석을 수행하여 함수형태로 나타내었다. 이러한 토석류 취약함수는 토석류 재해로 피해가 발생할 가능성이 있는 지역의 건물손상 정도를 정량적으로 평가하는 방법으로 이용할 수 있다. The physical characteristics of debris flows were analyzed from a total of 8 cases of debris flow disasters occurred in between July and August, 2011. 15 buildings damaged in these events were also investigated in detail to study the characteristics and patterns of building damages by debris flows. Physical vulnerability was obtained from the relationship of the degree of building damage and the physical characteristics of debris flow. Three different empirical vulnerability curves were obtained, which were functions of debris flow height, flow velocity and impact pressure, respectively. Furthermore, the vulnerability function was characterized according to the structural types of the building. In the case of non-concrete building, a complete destruction occurred at the impact pressure of more than 30 kPa, an extensive damage at the impact pressure between 15 and 30 kPa, a slight damage at the impact pressure below 15 kPa. In the case of reinforced-concrete buildings, an extensive damage occurred at the impact pressure of more than 100 kPa, a moderate damage at the impact pressure between 35 and 100 kPa, a slight damage at the impact pressure below 35 kPa. The impact pressure of debris flow corresponding to a slight damage to the reinforced-concrete building produced a complete damage for the case of non-concrete building, Nonlinear regression analysis was performed according to the physical characteristics of debris flow and the building structural type. The proposed physical vulnerability curves could be used as a quantitative assessment of the structural resistance of buildings affected by a debris flow event.

Engineering measures for debris flow hazard mitigation in the Wenchuan earthquake area

Avalanches and landslides caused by the Wenchuan earthquake in the Longmen Mountains area provide abundant loose solids for debris flows, and a large number of debris flows have occurred during the period 2008–2012. The engineering measures in certain gullies failed, causing serious damage and loss of life. Judging from the debris flow characteristics in the Wenchuan earthquake area, engineering measures should be better constructed after the active period of debris flows in severely affected areas. To reduce debris flow disasters, this paper proposes a mitigation method and design principle based on the transport capacity of the main river. A series of check dams with various opening sizes was designed by investigating and analyzing existing cases. Furthermore, a new type of drainage channel with prefabricated reinforced concrete boxes is proposed. Finally, a case study of the Xiaogangjian Gully, which is a typical debris flow gully in the Wenchuan earthquake area, is presented. This system of engineering measures is based on the main river's transport capacity and consists of five check dams with various opening sizes, a drainage channel with sidewalls constructed of prefabricated reinforced concrete boxes, and a debris flow basin at the base of the main gully. The debris flow mitigation measures constructed in the Xiaogangjian Gully effectively resisted a debris flow with a 50-year return period that was triggered by rainfall on July 26, 2012. Specifically, these measures effectively protected a highway and minimized debris flow damage. Thus, the layout and engineered structures involved in this new engineering technique can provide a reference design for debris flow hazard mitigation.