Multi-hazard risk mapping and assessment on an active volcano: the GRINP project at Mount Cameroon

To help improve the safety of its population faced with natural disasters, the Cameroon Government, with the support of the French Government, initiated a programme of geological risk analysis and mapping on Mount Cameroon. This active volcano is subject to a variety of hazards: volcanic eruptions, slope instability and earthquakes. Approximately 450,000 people live or work around this volcano, in an area which includes one of Cameroon’s main economic resources. An original methodology was used for obtaining the information to reply to questions raised by the authorities. It involves several stages: identifying the different geological hazard components, defining each phenomenon’s threat matrix by crossing intensity and frequency indices, mapping the hazards, listing and mapping the exposed elements, analysing their respective values in economic, functional and strategic terms, establishing typologies for the different element-at-risk groups and assessing their vulnerability to the various physical pressures produced by the hazard phenomena, and establishing risk maps for each of the major element-at-risk groups (population, infrastructures, vegetation, atmosphere). At the end of the study we were able (a) to identify the main critical points within the area, and (b) provide quantified orders of magnitude concerning the dimensions of the risk by producing a plausible eruption scenario. The results allowed us to put forward a number of recommendations to the Cameroon Government concerning risk prevention and management. The adopted approach corresponds to a first level of response to the authorities. Later developments should make it possible to refine the quality of the methodology.     

Flood risk management in Central Viet Nam: challenges and potentials

This article explores the impacts of floods on the economy, environment, and society and tries to clarify the rural community’s coping mechanism to flood disasters in Central Viet Nam. It focuses on the social aspects of flood risk perception that shapes the responses to floods. The research findings revealed that flooding is an essential element for a coastal population, whose livelihood depend on productive functions of cyclical floods. The findings also revealed that floods, causing losses and damages, often inhibited economic development. The surveyed communities appeared to have evolved coping mechanisms to reduce the negative impacts of the floods, yet these coping mechanisms are under pressure due to environmental degradation. Integrated flood risk management is considered as a suitable paradigm for coping with flood disasters.

考虑时间效应的滑坡风险评估和管理

提出了考虑时间效应的滑坡风险评估和管理方法。以香港地区近20年的16 000个切破的观测资料为基础,从统计学的角度提出了边坡的时变可靠性分析方法。推导了新建边坡在未来服役时间内的年失效概率的计算公式,并对现役边坡在未来服役时间内的年失效概率进行了预测。确定了基于年死亡人数的滑坡风险接受准则,并分析了基于滑坡时变风险的边坡加固时间。结果表明,考虑时间效应的滑坡风险评估和管理方法能够更加真实地反映滑坡随时间变化的特性。新建边坡的年失效概率随边坡服役时间逐渐增大,尤其是当边坡服役超过10年时,每年发生滑坡的概率急剧增大。现役边坡的年失效概率基本与继续服役时间呈线形关系。此外,香港斜坡维修指南规定的边坡加固时间能够有效地将滑坡风险降低到ALARP区或可接受的风险区。     

滑坡风险评价难点及方法综述

滑坡风险评价是从国外引进的新理念和新方法,国内目前对此的理解和应用,甚至概念都有混淆之处;同时又由于"风险"的本质是一种未来事件的不确定性,对其评价也有诸多困难。本文根据当今国际上通用的滑坡风险管理理论,得出风险评价要素,进而分析出进行滑坡风险评价的难点,从滑坡的空间预测、时间预测、滑移距离预测和强度预测四个方面,综述了国内外在这些难点上进行量化和评价的技术方法,并对各种方法的优缺点和适用性进行了评述。     

Drought risk assessment in the western part of Bangladesh

Though drought is a recurrent phenomenon in Bangladesh, very little attention has been so far paid to the mitigation and preparedness of droughts. This article presents a method for spatial assessment of drought risk in Bangladesh. A conceptual framework, which emphasizes the combined role of hazard and vulnerability in defining risk, is used for the study. Standardized precipitation index method in a GIS environment is used to map the spatial extents of drought hazards in different time steps. The key social and physical factors that define drought vulnerability in the context of Bangladesh are identified and corresponding thematic maps in district level are prepared. Composite drought vulnerability map is developed through the integration of those thematic maps. The risk is computed as the product of the hazard and vulnerability. The result shows that droughts pose highest risk to the northern and northwestern districts of Bangladesh.     

Integrated model for earthquake risk assessment using neural network and analytic hierarchy process:Aceh province,Indonesia

Catastrophic natural hazards,such as earthquake,pose serious threats to properties and human lives in urban areas.Therefore,earthquake risk assessment(ERA)is indispensable in disaster management.ERA is an integration of the extent of probability and vulnerability of assets.This study develops an integrated model by using the artificial neural network–analytic hierarchy process(ANN–AHP)model for constructing the ERA map.The aim of the study is to quantify urban population risk that may be caused by impending earthquakes.The model is applied to the city of Banda Aceh in Indonesia,a seismically active zone of Aceh province frequently affected by devastating earthquakes.ANN is used for probability mapping,whereas AHP is used to assess urban vulnerability after the hazard map is created with the aid of earthquake intensity variation thematic layering.The risk map is subsequently created by combining the probability,hazard,and vulnerability maps.Then,the risk levels of various zones are obtained.The validation process reveals that the proposed model can map the earthquake probability based on historical events with an accuracy of 84%.Furthermore,results show that the central and southeastern regions of the city have moderate to very high risk classifications,whereas the other parts of the city fall under low to very low earthquake risk classifications.The findings of this research are useful for government agencies and decision makers,particularly in estimating risk dimensions in urban areas and for the future studies to project the preparedness strategies for Banda Aceh.     

Landslide risk assessment and management by decision analytical procedure for Dereköy, Konya, Turkey

The Dereköy landslide threatening the town of Dereköy, Konya, Turkey is investigated in order to assess and manage the associated risk. Dereköy town, located 12 km west of Konya city center, which is the second largest city in central Anatolia, has been extending due to the demand for new settlement places in Konya for the last decade. As most of the town is situated on the slopes of Meram river valley, on which the slope movements are observed, the risk of landslide has been increasing due to these new settlements. In this study, the landslide risk in Dereköy is assessed by following the so-called decision analytical procedure. The risk is defined by multiplication of hazard and consequences of the hazard. The hazard, which is the probability of slope failure, is computed by using the first-order second-moment (FOSM) method. The possible consequences of a landslide in Dereköy are analyzed and their costs are assessed relative to each other. A decision tree for choosing among the possible alternatives for reducing the risk is constructed in order to manage the risk.     

滑坡风险评价的理论与方法研究

作为防灾减灾的重要措施之一,滑坡风险评价已经成为近年来国际上滑坡研究的热点,并形成了较为完备的滑坡风险管理体系。国内的滑坡风险研究则起步较晚,滑坡风险评价的关键支撑技术体系尚未建立。本文对滑坡风险评价中的关键理论和方法进行梳理,阐述了国际滑坡风险评价的理论框架和技术流程,介绍了国内外滑坡易发性、危险性和风险评价的最新进展,评述了滑坡易发性评价、扩展范围预测、频率分析以及承灾体易损性评价的主要方法,阐明了现阶段滑坡风险评价的重点领域和前沿科学问题,并对滑坡灾害的风险评价提出了三点展望。     

Landslides in Emilia-Romagna region (Italy): strategies for hazard assessment and risk management

In Emilia-Romagna, over 32,000 landslide bodies cover one-fifth of the hilly and mountainous territory. The majority of them originated as earth-flows after the last glacial maximum and grew during the rainiest periods of the Holocene through the superimposition of new earth-flows. Reactivation of these large landslides is the main problem the geologists of Emilia-Romagna are facing now. Intense and/or prolonged precipitation play a major role as triggering factors in reactivating landslide bodies, but also the importance of snowmelt is suggested by the monthly distribution of landslide events. Almost all the present-day landslide activity is due to the reactivation of pre-existing landslide bodies. Consequently, territorial planning and geo-thematic cartography are fundamental tools for the reduction of risk. The Emilia-Romagna geo-thematic cartography (1:10,000) is legally binding and regulates land use in regional, municipal and basin plans.     

Kinematics and 3-D internal deformation of granular slopes: Analogue models and natural landslides

This study uses results from a series of analogue models, and field observations, scanned data and sections of natural landslides to investigate the kinematics and internal deformation during the failure of an unstable slope. The models simulate collapse of granular slopes and focus on the spatial and temporal distribution of their internal structures. Using a series of systematically designed models, we have studied the effect of friction and deformability of the runout base on internal deformation within a granular slope. The results of these different models show that the collapse of granular slopes resulted in different-generation extensional faults at the back of the slope, and contractional structures (overturned folds, sheath folds and thrusts) at the toe of the slope. The failure surfaces and the volume of the failure mass changed both spatially and temporally. Younger failure surfaces formed in the back of the older ones by incorporating additional new material from the head of the slope. Our model results also show that the nature of the runout base has a significant influence on the runout distance, topography and internal deformation of a granular slope. Model results are compared with natural landslides where local profiles were dug in order to decipher the internal structures of the failure mass. The natural cases show similar structural distribution at the head and toe of the failure mass. As in model results, our field observations indicate the presence of at least two generations of failure surfaces where the older ones are steeper.     

Spatial data for landslide susceptibility, hazard, and vulnerability assessment: An overview

The aim of this paper is to discuss a number of issues related to the use of spatial information for landslide susceptibility, hazard, and vulnerability assessment. The paper centers around the types of spatial data needed for each of these components, and the methods for obtaining them. A number of concepts are illustrated using an extensive spatial data set for the city of Tegucigalpa in Honduras. The paper intends to supplement the information given in the “Guidelines for Landslide Susceptibility, Hazard and Risk Zoning for Land Use Planning” by the Joint ISSMGE, ISRM and IAEG Technical Committee on Landslides and Engineered Slopes (JTC-1). The last few decades have shown a very fast development in the application of digital tools such as Geographic Information Systems, Digital Image Processing, Digital Photogrammetry and Global Positioning Systems. Landslide inventory databases are becoming available to more countries and several are now also available through the internet. A comprehensive landslide inventory is a must in order to be able to quantify both landslide hazard and risk. With respect to the environmental factors used in landslide hazard assessment, there is a tendency to utilize those data layers that are easily obtainable from Digital Elevation Models and satellite imagery, whereas less emphasis is on those data layers that require detailed field investigations. A review is given of the trends in collecting spatial information on environmental factors with a focus on Digital Elevation Models, geology and soils, geomorphology, land use and elements at risk.     

Landslide risk assessment using concepts of danger pixels and fuzzy set theory in Darjeeling Himalayas

Landslide risk assessment (LRA) is a key component of landslide studies. The landslide risk can be defined as the potential for adverse consequences or loss to human population and property due to the occurrence of landslides. The LRA can be regional or site-specific in nature and is an important information for planning various developmental activities in the area. LRA is considered as a function of landslide potential (LP) and resource damage potential (RDP). The LP and RDP are typically characterized by the landslide susceptibility zonation map and the resource map (i.e., land use land cover map) of the area, respectively. Development of approaches for LRA has always been a challenge. In the present study, two approaches for LRA, one based on the concept of danger pixels and the other based on fuzzy set theory, have been developed and implemented to generate LRA maps of Darjeeling Himalayas, India. The LRA map based on the first approach indicates that 1,015 pixels of habitation and 921 pixels of road section are under risk due to landslides. The LRA map derived from fuzzy set theory based approach shows that a part of habitat area (2,496 pixels) is under very high risk due to landslides. Also, another part of habitat area and a portion of road network (7,204 pixels) are under high risk due to landslides. Thus, LRA map based on the concept of danger pixels gives the pixels under different resource categories at risk due to landslides whereas the LRA map based on the concept of fuzzy set theory further refines this result by defining the degree of severity of risk to these categories by putting these into high and low risk zones. Hence, the landslide risk assessment study carried out using two approaches in this paper can be considered in cohesion for assessing the risks due to landslides in a region.     

Comparative Analysis of Risk Assessment of Landslides and Debris Flows of China in 2000 and 2010

Landslides and debris flows occurr in China frequently and cause disastrous losses of life and property. The risk assessment of landslides and debris flows and their spatial variations were comparatively analyzed in this paper, which has great significance for disaster prevention. This article selected 1 km×1 km grid as the assessment unit and with support of GIS technique, analyzed landslide and debris-flow risk distribution and their spatial variations from 2000 to 2010. The research results indicated that the spatial distribution of risk classes in 2000 and 2010 was obviously discrepant. Overall, taking the Heihe-Tengchong population density line as the boundary, the west of the line is mainly low risk area; the east of the line is mainly high risk area. Compared with the risk of 2000, the risk values of 2010 increased, with the high risk area and low risk area enlarged, moderate risk area reduced. The moderate risk area is the most unstable and sensitive risk area, and its risk class variation is significant. However, China is not a region with the high risk of landslide and debris-flow hazard at present. In the following next 10 years, the risk of landslides and debris flows in China will continue to increase.     

Groundwater contamination: risk management and assessment for landfills in Mar del Plata, Argentina

 This study presents a program for risk management in the contamination of groundwater resulting from leachate in landfills at Mar del Plata (Argentina). The program includes prediction, prevention, monitory observation and mitigation as actions that must be taken prior to, during, and after contamination occurs. This routine aids in the identification of weak points and failures of the program for those who are in charge of making decisions, and will allow better use of limited financial and technical resources based on planning, thus minimizing disconnected determinations. Results of the prediction stage were confirmed through monitoring. The presence of a plume of contamination more than 100 m from the landfill was shown, thus proving that implementation of a monitoring plan to follow the development of the contaminated plume must be implemented, particularly in populated areas which depend on residential wells for their water supply. Received: 8 May 2000 · Accepted: 14 August 2000     

Geology as a control on landslides on the Isle of Wight: an overview

The Cretaceous and Palaeogene sedimentary rocks that crop out on the Isle of Wight are highly prone to landsliding and the island offers an important field laboratory wherein to investigate a number of the different types of failure. Many of these landslides represent a significant engineering hazard, with several urban areas requiring remedial work and planning constraints (e.g. The Undercliff and Seagrove Bay) to aid development. Previous studies have thoroughly investigated the major landslides in the Undercliff area around Ventnor and presented a mechanism for that massive failure. This overview of the landslides throughout the Isle of Wight by the British Geological Survey was completed as part of the multidisciplinary survey of the surface geology, structure, geophysical response and offshore interpretations of the island between 2007 and 2010. The survey has collected new observational data on the extensive coastal landslides, as well as the distribution, nature and mechanism of failure of the lesser-studied inland examples.     

遥感在滑坡灾害研究中的应用进展

在对常用的光学遥感卫星影像、InSAR,LiDAR等遥感技术方法介绍的基础上,综述了这些方法在滑坡研究中的最新应用进展,从滑坡风险评估中的基础地形数据获取、滑坡编录与制图、监测、滑坡因素制图、承灾体制图等5个方面阐述遥感技术在滑坡风险中的支撑技术作用与应用前景。从遥感影像在滑坡风险评估中的作用、解译能力、影响解译的因素、精度评价和遥感数据源选择等角度阐述了常用遥感技术在滑坡风险评估应用中存在的问题,认为: ① 遥感技术在滑坡风险评估中的主要作用为数据、信息的获取与更新;② 滑坡的遥感影像解译能力取决于影像空间分辨率与待识别滑坡大小的相对关系,影像的时间分辨率、滑坡与其周边环境的对比度、立体影像的获取能力是利用遥感影像开展滑坡探测、识别与制图的关键要素;解译方法和解译员的专业素质是滑坡遥感解译的重要影响因素;③ 遥感影像与GIS空间分析、3D可视化的综合可有效增强滑坡识别与制图的效率和精度;④ 对于遥感解译滑坡的精度评价应针对具体影像的可解译性从有效解译,错误解译和遗漏解译三个方面予以客观评价;⑤ 滑坡风险评估应针对具体应用,从成本效益比的角度,本着“够用为止”原则合理选用遥感数据源。     

Resilient capacity assessment for geological failure areas: examples from communities affected by debris flow disaster

This study establishes a novel method for assessing the community resilient capacity of debris flow disasters with appropriate parameters, such as responding, monitoring and communication capabilities. This study adopts eight communities in Taiwan, namely Nangang, Tongfu, Jhongyang, Laiyuan, Chingfu, Sinsheng, Shangan and Jyunkeng, as examples. First, the Analytic Hierarchy Process was applied to establish the framework of the community resiliency capacity, including the community’s resources for disaster resilience and resident capabilities. The community’s resources for disaster resilience are identified by surveying the community leaders via checklists. Resident capabilities are determined using questionnaires. The community resilient capacity refers to the sum of the results from these two investigations. The two investigations have similar weights, indicating that they are equally significant when evaluating community resilient capacity. Second, FLO-2D software is utilized for hazard analysis by simulation results of deposited areas for debris flows, and then these areas were categorized according to hazard degrees. Finally, the vulnerability of communities is classified based on the land use type. In summary, the values of capacity, hazard and vulnerability are integrated to determine the risk of debris flow for each community. A risk map is then generated.     

Landslide hazards and mitigation measures at Gangtok, Sikkim Himalaya

Landslides and other mass movements are serious geo-environmental hazards in the Himalayas. Massive landslides killing tens of thousands of people with catastrophic damages have occurred in the Eastern Himalayan State of Sikkim, which shares common borders with Tibet, Nepal, and Bhutan. This paper describes the investigations carried out on recent landslides in Gangtok, Sikkim, India, with emphasis on the triggering mechanisms that have contributed to the release and creep of natural slopes in the region. It is believed that the intense rainfall in the region not only contributes to rapid erosion and weathering of the rock mass, but also increases the groundwater level that leads to reduction in the stability of natural slopes. A landslide instrumentation programme that includes placement of settlement pillars and piezometers is underway to predict the behaviour of landslides in the area.