Implementing low-cost landslide risk reduction: a pilot study in unplanned housing areas of the Caribbean

Landslides pose a serious physical and environmental threat to vulnerable communities living in areas of unplanned housing on steep slopes in the Caribbean. Some of these communities have, in the past, had to be relocated, at costs of millions of dollars, because of major slides triggered by tropical storm rainfall. Even so, evidence shows that: (1) risk reduction is a marginal activity; (2) there has been minimal uptake of hazard maps and vulnerability assessments and (3) there is little on-the-ground delivery of construction for risk reduction. This article directly addresses these issues by developing a low-cost approach to the identification of the potential pore pressure changes that trigger such slides we seek to address these three commentaries directly. A complex 45–60° slope site in St Lucia, West Indies was selected as a pilot for a modelling approach that uses numerical models (FLAC and CHASM) to verify the need for surface water management to effectively reduce landslide risk. Following the model confirmation, a series of drains were designed and constructed at the site. Post-construction evidence indicates the methodology to be sound, in that the site was stable in subsequent 1-in-1 to 1-in-4 year rainfall events. A critical feature of the approach is that it is community-based from data acquisition through to community members participating in construction.     

Annual landslide risk and effectiveness of risk reduction measures in Shihmen watershed,Taiwan

Landslide risk analysis procedures in this study could evaluate annual landslide risk, and assess the effectiveness of measures. Risk analysis encompassing landslide hazard, vulnerability, and resilience capacity was used to evaluate annual landslide risk. First, landslide spatial, temporal, and area probabilities were joined to estimate annual probability of landslides with an area exceeding a certain threshold in each slope unit. Second, different elements were assigned corresponding values and vulnerabilities to calculate the expected property and life losses. Third, the resilience capacities of communities were calculated based on the scores obtained through community checklists and the weights of items, including “the participation experience of disaster prevention drill,” “real-time monitoring mechanism of community,” “autonomous monitoring of residents,” and “disaster prevention volunteer.” Finally, the annual landslide probabilities, expected losses, and resilience capacities were combined to evaluate annual landslide risk in Shihmen watershed. In addition, annual risks before and after the implementation of measures were compared to determine the benefits of measures, and subsequently benefit–cost analysis was performed. Communities with high benefit–cost ratios included Hualing, Yisheng, Siouluan, and Gaoyi. The watershed as a whole had a benefit–cost ratio far greater than 1, indicating the effectiveness of measures was greater than the investment cost. The results of factor sensitivity analysis revealed changes in vulnerabilities and mortality rates would increase the uncertainty of risk, and that raise in annual interest rates or reduction in life cycle of measures would decrease the benefit–cost ratio. However, these changes did not reverse the cost-effective inference.     

An integrated GIS-based approach for geohazards risk assessment in coal mines

From the viewpoint of safety in underground coal mining, the most suitable mining panel is the one with minimum geological structures, the right machinery, and equipment selection, trained employee, and proficient stope management. Since the ground parameters are uncontrollable and inherent uncertainties exist, a high percent of risk will usually accompany the underground coal mining activities. The main purpose of this study is to present a geological–geotechnical risk assessment model for identification of high risk-prone areas in underground coal mines using an integrated GIS-geostatistics system. Tabas as the first mechanized and largest underground coal mine in Iran was selected as a case study in this study. Gas content of coal seam, Coal Mine Roof Rating (CMRR), initial in situ stress state, fault throw, and orientation were selected as hazard/risk factors. For estimating the amount of coal seam gas content, CMRR and initial in situ stress in unsampled areas and providing the prediction maps, geostatistics module in ArcGIS was used. Rock engineering system–interaction matrix method was used for attribute weight assignment. Next, the attribute layers were weighted, rated, and overlaid to create a final map of geohazards risk. The analysis results of final risk map indicate that about 45% of under study area is prone to high to very high geohazards risk. Comparison of the results with experiences obtained during the early part of the mine and mined-out panels showed generally good agreement with promising ideas. This highlights the potential application of the GIS-based approach for hazards detection and geohazards risk assessment in underground coal mines.     

砂浆锚杆加固效果的等效数值模拟方法研究

针对常规数值模拟计算无法有效地反映锚杆对围岩的加固效果的缺陷,结合岩体变形在锚杆中产生的支护压力计算公式,提出了一种简单、有效的砂浆锚杆加固等效数值模拟方法。该方法首先在有锚杆支护隧道开挖的计算结果中提取每根锚杆的最大轴力;然后根据该轴力值按锚杆支护压力公式计算其所产生的等效均布力;最后将该均布力施加到相同计算工况下无锚杆支护的围岩表面进行模拟计算。将该方法应用于锦屏二级水电站地下厂房枢纽洞室及乌东德水电站4#导流洞0+ 550 m断面的开挖与支护计算,通过与现场实测数据对比,结果表明,该方法能较好地模拟锚杆支护对围岩的加固效果,其模拟结果可为隧洞的施工与支护设计提供可靠的参考依据。     

An acoustic emission landslide early warning system for communities in low-income and middle-income countries

Early warning systems for slope instability are needed to alert users of accelerating slope deformation behaviour, enable evacuation of vulnerable people, and conduct timely repair and maintenance of critical infrastructure. Communities exposed to landslide risk in low- and middle-income countries seldom currently instrument and monitor slopes to provide a warning of instability because existing techniques are complex and prohibitively expensive. Research and field trials have demonstrated conclusively that acoustic emission (AE) monitoring can be an effective approach to detect accelerating slope movements and to subsequently communicate warnings to users. The objective of this study was to develop and assess a simple, robust, low-cost AE monitoring system to warn of incipient landslides, which can be widely deployed and operated by communities globally to help protect vulnerable people. This paper describes a novel AE measurement sensor that has been designed and developed with the cost constrained to a few hundred dollars (US). Results are presented from physical model experiments that demonstrate performance of the AE system in measuring accelerating deformation behaviour, with quantifiable relationships between AE and displacement rates. Exceedance of a pre-determined trigger level of AE can be used to communicate an alarm to users in order to alert them of a slope failure. Use of this EWS approach by communities worldwide would reduce the number of fatalities caused by landslides.     

基于最小二乘三维表面匹配算法的滑坡变形测量

针对已有利用地面三维激光扫描(TLS)技术实施变形测量的局限性,如变形提取的一维性及对小变形的不敏感性。提出了一个基于重复扫描数据实施滑坡变形监测的新方法,该方法主要包括3个步骤：原始TLS数据的获取、TLS数据的总体配准以及基于子区域的变形计算。其核心是给出的一种三维表面匹配新算法（最小二乘2维图像匹配的泛化）。该方法可充分利用TLS数据的高冗余性,实现高精度的全三维变形测量,得到监测对象的位移量和旋转量,同时,在应用上具有高度的灵活性。通过模拟试验验证了该方法的性能。此外,利用该方法分析了一个滑坡变形监测实例,进一步证实了模拟试验的结果。该方法适用于变形监测,尤其是人员难以到达的面灾害监测领域。对促进变形监测从点测绘向形测绘的转变具有一定的实际意义。     

The role of faith-based institutions in urban disaster risk reduction for immigrant communities

Natural Hazards - Drawing on interviews with Cambodian and Thai communities in Auckland, New Zealand, this paper examines the role of Buddhist temples in disaster preparedness, response and...     

A multidisciplinary approach to evaluating impacts of shellfish aquaculture on benthic communities

The impact of suspended mussel culture (Mytilus edulis, M. trossulus) on the benthos of a small Nova Scotia cove (7 m depth) was assessed using meehods involving both benthic metabolism and community structure. Due to deposition of mussel feces and pseudofeces, sedimentation rate was higher under the mussel culture lines than at an adjacent reference site of similar sediment texture. Porewater profiles of sediment sulfate and sulfide indicated greater anaerobic metabolism at the mussel site than at the reference site, but sulfide was absent from the upper centimeters of sediments under the mussels. Seasonal measures of sediment oxygen demand showed little change between sites, but maximum rates of ammonium release at the mussel site were twice the highest rates measured at the reference site. Abundance of benthic macrofauna was higher at the reference site, but biomass was generally lower. Biomass at the mussel site was dominated by molluscs (Ilyanassa spp. andNucula tenuisulcata), that were attracted to mussels fallen from the culture and/or enriched organic matter due to biodeposition. Species diversity was lower at the reference site due to the dominance of the polychaeteNephtys neotena. Abundance-biomass comparisons (ABC method) of faunal analysis did not indicate any impact of biodeposition at this site: however, disturbance did not result in a typical assemblage of small opportunistic species anticipated with this method. Cluster analysis of macrofauna usually provided a clear separation between the sites. Since the contruction of a causeway (1968), foraminifera species composition showed a temporal response to temperature changes in the cove by shifting toward calcareous species, but assemblages downcore showed little or no relationship to aquaculture impacts. Although there is a shift toward anaerobic metabolism at the mussel lines, the impact of mussels falling to the sediments was more noticeable in benthic community structure than was any impact due to organic sedimentation or hypoxia. In general the impact of aquaculture on the benthos appeared to be minor. Furtyher assesment of these consequences may mandate both taxonomic and energetic approaches to impact assessment.     

A systematic approach for the assessment of flooding hazard and risk associated with a landslide dam

Inundation caused by landslide dams may occur in the upstream and downstream of the dams. A proper flooding hazard assessment is required for reaction planning and decision-making to mitigate possible flooding hazards caused by landslide dams. Both quick and detailed procedures can be used to evaluate inundation hazards, depending on the available time and information. This paper presents a systematic approach for the assessment of inundation hazards and risks caused by landslide dam formation and breaches. The approach includes the evaluation of dam-breach probability, assessment of upstream inundation hazard, assessment of downstream inundation hazard, and the classification of flooding risk. The proposed assessment of upstream inundation estimates the potential region of inundation and predicts the overtopping time. The risk level of downstream flooding is evaluated using a joint consideration of the breach probability of a landslide dam and the level of flooding hazard, which is classified using a flooding hazard index that indicates the risk of potential inundation. This paper proposes both quick and detailed procedures for the assessments of inundation in both the upstream and downstream of a landslide dam. An example of a landslide dam case study in southern Taiwan was used to demonstrate the applicability of the systematic approach.     

Landslide catastrophes and disaster risk reduction: A GIS framework for landslide prevention and management

A detailed and accurate inventory map of landslides is crucial for quantitative hazard assessment and land planning. Traditional methods relying on change detection and object-oriented approaches have been criticized for their dependence on expert knowledge and subjective factors. Recent advancements in high-resolution satellite imagery, coupled with the rapid development of artificial intelligence, particularly data-driven deep learning algorithms (DL) such as convolutional neural networks (CNN), have provided rich feature indicators for landslide mapping, overcoming previous limitations. In this review paper, 77 representative DL-based landslide detection methods applied in various environments over the past seven years were examined. We analyze the structures of different DL networks, discuss on five main application scenarios, and assess both the advancements and limitations of DL in geological hazard analysis. The results indicated that the increasing number of articles per year reflects growing interest in landslide mapping by artificial intelligence, with U-Net-based structures gaining prominence due to their flexibility in feature extraction and generalization. Finally, we explored the hindrances of DL in landslide hazard research based on the above research content. Challenges such as black-box operations and sample dependence persist, warranting further theoretical research and future application of DL in landslide detection.     

An integrated approach for validating unsaturated soil parameters in seepage analyses

Soil–water characteristic curves (SWCCs) and soil permeability functions (SPFs) for a silty sand were validated based on soil suction and soil water content measurements in calibration box and constant-head seepage tests. Transient seepage analyses using finite element method (FEM) were performed to examine the accuracy of the derived SWCCs and SPFs, with a special focus on the wetting front propagation. Results show that the proposed new integrated system consisting of experimental and analytical techniques works well, in the sense that the soil moisture responses at specific depths of soil mimic those measured in constant-head seepage tests.     

An approach for GIS-based statistical landslide susceptibility zonation—with a case study in the Himalayas

Landslide susceptibility zonation (LSZ) is necessary for disaster management and planning development activities in mountainous regions. A number of methods, viz. landslide distribution, qualitative, statistical and distribution-free analyses have been used for the LSZ studies and they are again briefly reviewed here. In this work, two methods, the Information Value (InfoVal) and the Landslide Nominal Susceptibility Factor (LNSF) methods that are based on bivariate statistical analysis have been applied for LSZ mapping in a part of the Himalayas. Relevant thematic maps representing various factors (e.g., slope, aspect, relative relief, lithology, buffer zones along thrusts, faults and lineaments, drainage density and landcover) that are related to landslide activity, have been generated using remote sensing and GIS techniques. The LSZ derived from the LNSF method, has been compared with that produced from the InfoVal method and the result shows a more realistic LSZ map from the LNSF method which appears to conform to the heterogeneity of the terrain.     

Evaluation of drainage tunnel effectiveness in landslide control

Infiltration of rainfall into hillslopes is often an important factor in triggering landslides. Using underground water drainage works together with anti-slide piles has been an effective method of landslide control, yet their effectiveness is inadequately discussed in the literature. This paper studies the influence of rainfall on the change in the underground water level beneath a slope by real-time and synchronic monitoring of the rainfall, the underground water level in the boreholes, and the flow rate of the underground drainage tunnel. The effectiveness of the underground drainage tunnel in preventing the rise of the underground water level of the slope is discussed. The researchers also study the deformation behavior of the anti-slide piles by monitoring the lateral displacement of the piles and analyzing the thrust that the anti-slide piles bear by numerical inversion techniques. The results indicate that there is an apparent relationship between the lag in the rising of the underground water level caused by a rainfall and that caused by the immediately previous rainfall. When there is a rainfall accumulation before the occurrence of a heavy rain, this particular heavy rainfall will cause a rapid rise of the underground water level beneath the slope. The monitoring data analysis shows that the flow rate of the underground drainage tunnel increases first, and then the underground water level of the slope rises after a rainfall. In other words, the flow rate of the underground drainage tunnel increases at a rate faster than that of the rise of the underground water level. Hence, the underground drainage tunnel can effectively lower the rise of the underground water level induced by a rainfall. Besides, based on the monitoring data of the lateral displacement of the anti-slide piles and subsequent analysis, the working state of the anti-slide piles is justified. It thus indirectly validates the benefits of using underground drainage tunnel in landslide control.     

综合测井在滑坡勘查中的应用

综合四川省汉源县城后山的滑坡勘查工作,介绍了采用综合测井方法在确定滑坡滑面位置和滑体厚度中的应用,取得了较好的效果。     

An improved approach for evaluating the time-dependent stability of colluvial landslides during intense rainfall

The paper presents an improved analytical approach for evaluating the time-dependent stability of colluvial landslides during intense rainfall infiltration. The approach comprises two steps: first to simulate rainfall infiltration and then to compute the safety factor. In terms of the irregularity of the natural landslide surface in implementation of the method, the landslide is divided into several soil slices with approximately straight sides. Each single slice is regarded as a finite slope so that the infiltration formula and safety factor can be deduced. The infiltration formula is derived with combination of the Green–Ampt model and mass conservation law considering seepage perpendicular and parallel to slope surface simultaneously. In the modified infiltration model, both size effect and angle effect are vividly observed in the process of rainfall infiltration into the finite slope, while the former of which is not presented in the original Green–Ampt model. The safety factor is computed using the limit equilibrium method, with the influence of infiltrating water on the shear strength, gravity and seepage force of soil slices considered. By case study of the Shuping landslide in Three Gorges, decline in the safety factor and the decrease in the tendency are definite. Specifically under the rainfall intensity of 50 mm/h, the failure of Shuping landslide is most likely to occur at the time of 102 h. In addition, the results highlight shallow failure along the wetting front under intense rainfall.     

Assessment of the influence of physical and seismotectonic parameters on landslide occurrence: an integrated geoinformatic approach

Natural Hazards - Landslide is a devastating natural hazard, which causes significant losses of human lives and properties. The landslide occurrences are the perennial problem in Himalayan region...     

An integrated flood risk assessment model for property insurance industry in Taiwan

Taiwan is located in an area affected by Northwest Pacific typhoons, which are also one of the most important sources of rainfall to the island. Unfortunately, the abundant rainfall brought by typhoons frequently produces hazards. In recent years, typhoons and floods have caused serious damage, especially Typhoon Morakot in 2009. In this study, a probabilistic model is developed based on historical events which can be used to assess flood risk in Taiwan. There are 4 separate modules in this model, including a rainfall event module, a hydraulic module, a vulnerability module, and a financial loss module. Local data obtained from the Taiwan government are used to construct this model. Historical rainfall data for typhoon and flood events that have occurred since 1960, obtained from the Central Weather Bureau, are used for computing the maximum daily rainfall for each basin. In addition, the latest flood maps from the Water Resources Agency are collected to assess the probable inundation depth. A case study using the local data is carried out. Assessment is made to predict possible economic loss from different financial perspectives such as the total loss, insured loss, and loss exceeding probabilities. The assessment results can be used as a reference for making effective flood risk management strategies in Taiwan.