Landslide Hazard Evaluation Research Articles

Rainfall triggering soil slips in the southern Apuan Alps (Tuscany, Italy)

Abstract. The Apuan Alps are characterized by frequent heavy rainfall. In several cases this triggered many shallow landslides (soil slips). With the aim of contributing to the landslide hazard evaluation of the southern Apuan Alps (upper Versilian area), a detailed analysis of the main pluviometric events was carried out. Data recorded at the main raingauge of the area from 1975 to 2002 were analysed and compared with the occurrence of soil slips, in order to examine the relationship between soil slip initiation and rainfall. Some thresholds for soil slip-debris flow activity in terms of mean intensity, duration and mean annual precipitation (MAP) were defined for the study area.

Reservoir sedimentation associated with landsliding, Atrak watershed, Iran

The Barezoo dam on the Gholjogh River, a branch of the Atrak River with a catchment area of 491.7 km 2 , is located about 18 km north of Shirvan city in NE Iran. Landslides are an important natural hazard in the Atrak watershed and cause serious problems for the maintenance of the Barezoo reservoir. Landslide occurrence is controlled by lithology, slope of the terrain, and natural and human actions that may either add to the operating gravitational stresses or reduce the resistance to sliding of the soils forming the slope. The interaction between local geology and climatic conditions in this area has resulted in landforms with varying degrees of susceptibility to landsliding. Dammed watersheds in NE Iran experience numerous landslide and sedimentation problems. A quantitative approach based on a numerical rating scheme called the landslide hazard evaluation factor rating scheme was used to evaluate and describe landslides and their resultingsedimentation in the Gholjogh watershed.

Systems theory for risk evaluation of landslide hazard

Systems theory for risk evaluation of landslide hazard

Integration of spatial and temporal data for the definition of different landslide hazard scenarios in the area north of Lisbon (Portugal)

Abstract. A general methodology for the probabilistic evaluation of landslide hazard is applied, taking in account both the landslide susceptibility and the instability triggering factors, mainly rainfall. The method is applied in the Fanhões-Trancão test site (north of Lisbon, Portugal) where 100 shallow translational slides were mapped and integrated into a GIS database. For the landslide susceptibility assessment it is assumed that future landslides can be predicted by statistical relationships between past landslides and the spatial data set of the predisposing factors (slope angle, slope aspect, transversal slope profile, lithology, superficial deposits, geomorphology, and land use). Susceptibility is evaluated using algorithms based on statistical/probabilistic analysis (Bayesian model) over unique-condition terrain units in a raster basis. The landslide susceptibility map is prepared by sorting all pixels according to the pixel susceptibility value in descending order. In order to validate the results of the susceptibility ana- lysis, the landslide data set is divided in two parts, using a temporal criterion. The first subset is used for obtaining a prediction image and the second subset is compared with the prediction results for validation. The obtained prediction-rate curve is used for the quantitative interpretation of the initial susceptibility map. Landslides in the study area are triggered by rainfall. The integration of triggering information in hazard assessment includes (i) the definition of thresholds of rainfall (quantity-duration) responsible for past landslide events; (ii) the calculation of the relevant return periods; (iii) the assumption that the same rainfall patterns (quantity/duration) which produced slope instability in the past will produce the same effects in the future (i.e. same types of landslides and same total affected area). The landslide hazard is present as the probability of each pixel to be affected by a slope movement, and results from the coupling between the susceptibility map, the prediction-rate curve, and the return periods of critical rainfall events, on a scenario basis. Using this methodology, different hazard scenarios were assessed, corresponding to different rain paths with different return periods.

Probability of Failure Occurrence and Recurrence in Rock Slopes Stability Analysis

The paper illustrates the procedures for computing the probability of failure occurrence that represents the potential that a slope can undergo failure due to both the spatial variability of the structural and geomechanical aspects of the joint sets and the existing boundary conditions. The presented approach to a global probabilistic assessment of the rock slopes stability conditions is based on the analysis of the spatial variability of structural aspects of the rock mass, of the uncertainty in geomechanical properties, and of the occurrence probabilities of certain values of seismic forces and rainfall intensities. Finally, the probability of failure recurrence is computed taking into account occurrences, in time, of the external acting forces, so providing an evaluation of the rock slope landslide hazard, that is the probability that an instability event with a given intensity may occur within a reference time period.

Landslide Hazard Evaluation: The Landslide Hazard Curves

This paper presents an innovative, practical methodology to establish priorities for slope monitoring and the planning of stabilization works in large hilly areas. The study is based on the analysis of geological and geomorphological maps, identification of catchment areas, and the division of catchment areas into primary (with main stream) and secondary (without main stream) sub-basins. Attention was focused on secondary sub-basins and their characteristics: lithology; an ad hoc parameter \iq (related to the average rainfall, the size of the basin, and the width of the toe section), and the average slope inclination \ii. The technique presented enables the “landslide hazard curve,” unique for a given formation in homogenous areas with similar rainfall conditions and seismicity, to be drawn in a chart which features \iq and \ii. All the ascertained and assumed unstable areas represented in the chart are located above the landslide hazard curve. The study was carried out scientifically by taking into account engineering aspects (geological, geomorphological, hydrological, and geotechnical), which influence slope stability. Groundwater levels, important in mapping out landslide prone areas, were considered in the study by means of the parameter \iq.

Landslide hazard evaluation in and around the Ilam Hydropower Project, Eastern Nepal Himalaya

The paper describes the results of the engineering geological and landslide hazard evaluation studies carried out in and around the Ilam Hydropower Project, eastern Nepal. Various types of mass wasting phenomena such as gully erosion, bank undercutting, and landslides are observed along the Mai Khola, Puwa Khola and road corridors. Gully erosion and bank undercutting are common on the slopes adjacent to streams and gullies. Most of the landslides are located on the slopes of 25° to 40° whereas large rock falls are found on the slopes, which are steeper than 40°. South-facing dip slopes contain large landslides while north-facing slopes seem to be relatively stable. The population of translational slide is dominant in the study area and is found mostly on soil having a depth of 3-6 m. Most of the rock falls are confined in schistose gneiss and highly fractured quartzite. Generally, three sets of joints govern the failure pattern of rockslides. The main triggering factors for mass movement of the area are high intensity of rainfall, rock discontinuities, steep topography, poor vegetation and river scouring. Land use pattern of the area has also equally contributed to initiate the mass movements in the area. The high hazard zones for rock slopes were confined to the steep dip slopes with highly fractured rocks whereas soil slope hazard is confined to fault zones and south facing slope. The soil slope was found to be more hazardous than the rock slope. The main causative factors for the landslide hazard in the study area are steep slope, rock discontinuity, land use pattern, soil depth and rainfall.

A geomorphological approach to the estimation of landslide hazards and risks in Umbria, Central Italy

Abstract. We present a geomorphological method to evaluate landslide hazard and risk. The method is based on the recognition of existing and past landslides, on the scrutiny of the local geological and morphological setting, and on the study of site-specific and historical information on past landslide events. For each study area a multi-temporal landslide inventory map has been prepared through the interpretation of various sets of stereoscopic aerial photographs taken over the period 1941–1999, field mapping carried out in the years 2000 and 2001, and the critical review of site-specific investigations completed to solve local instability problems. The multi-temporal landslide map portrays the distribution of the existing and past landslides and their observed changes over a period of about 60 years. Changes in the distribution and pattern of landslides allow one to infer the possible evolution of slopes, the most probable type of failures, and their expected frequency of occurrence and intensity. This information is used to evaluate landslide hazard, and to estimate the associated risk. The methodology is not straightforward and requires experienced geomorphologists, trained in the recognition and analysis of slope processes. Levels of landslide hazard and risk are expressed using an index that conveys, in a simple and compact format, information on the landslide frequency, the landslide intensity, and the likely damage caused by the expected failure. The methodology was tested in 79 towns, villages, and individual dwellings in the Umbria Region of central Italy.

The Saguenay Fjord, Quebec, Canada: integrating marine geotechnical and geophysical data for spatial seismic slope stability and hazard assessment

In 1996 a major flood occurred in the Saguenay region, Quebec, Canada, delivering several km 3 of sediment to the Saguenay Fjord. Such sediments covered large areas of the, until then, largely contaminated fjord bottom, thus providing a natural capping layer. Recent swath bathymetry data have also shown that sediment landslides are widely present in the upper section of the Saguenay Fjord, and therefore, should a new event occur, it would probably expose the old contaminated sediments. Landslides in the Upper Saguenay Fjord are most probably due to earthquakes given its proximity to the Charlevoix seismic region and to that of the 1988 Saguenay earthquake. In consequence, this study tries to characterize the permanent ground deformations induced by different earthquake scenarios from which shallow sediment landslides could be triggered. The study follows a Newmark analysis in which, firstly, the seismic slope performance is assessed, secondly, the seismic hazard analyzed, and finally an evaluation of the seismic landslide hazard is made. The study is based on slope gradients obtained from EM1000 multibeam bathymetry data as well as water content and undrained shear strength measurements made in box and gravity cores. Ground motions integrating local site conditions were simulated using synthetic time histories. The study assumes the region of the 1988 Saguenay earthquake as the most likely source area for earthquakes capable of inducing large ground motions in the Upper Saguenay region. Accordingly, we have analyzed several shaking intensities to deduce that generalized sediment displacements will begin to occur when moment magnitudes exceed 6. Major displacements, failure, and subsequent landslides could occur only from earthquake moment magnitudes exceeding 6.75.

Hydrogeological monitoring and image analysis of a mudslide in Southern Italy

This paper describes a methodological example of a data-integration procedure to improve the knowledge of landslide hazard related to a seismic area in the southern Apennine (Italy). Attention is focused on remote sensing data. The analysis is validated using detailed topographical, geophysical, geotechnical and hydrogeological data as ground truth. The investigated phenomenon, which started at the end of 1993, is an earthflow. The presented methodology recommends the combined use of DEM, multi-temporal panchromatic visible aerial photographs and thermal infrared images. The integration between these data and multidisciplinary monitoring data proved useful. The main hydrogeological pattern, the geological and geomorphological framework and the areas of latent instability can be clearly determined. Insight can be gained through the synoptic slope view in the relative short time needed to carry out the analysis. The proposed approach can be regarded as a useful contribution to the evaluation of landslide hazard, particularly during emergency periods.

Landslide hazards in eastern Himalayas

The Himalayas, with extreme variations in relief, are characterised by very steep slopes, harsh (i.e. cold and humid) climate and a dynamic geotectonic setting. These characteristics appear responsible for widespread slope failures and mass movements, which are often accentuated by various human activities. The importance and severity of landslide phenomenon was not recognised until recently because of sparse habitation, remoteness of its occurrence, and limited sphere of influence of the individual slides. During the last few decades, increasing developmental activities, such as unplanned urbanization, communication, dam construction, deforestation, and agriculture, have substantially affected the geo-environment and aggravated the landslide hazard in the eastern Himalayas.
 Three sample areas: i) along the National Highway 31 A (the East Sikkim District), ii) in the area of the Rarnmarn Hydroelectric Project Stage II (the Darjeeling District), and iii) in the Kalimpong Municipal area (the Darjeeling District), all within the inner tectonic belt of the Lesser Himalaya, were investigated for preparing LHZ maps on 1:25,000 scale. Landslide hazard evaluation factors (LHEF) were rated for each of the major causative factors, namely lithology, structure, slope morphometry, relative relief, land use, and drainage density, and summed up to obtain the total estimated hazard (TEHD) values for each slope facet. The TEHD values from 0 to 10 were classified into live zones of increasing relative hazard.

Landslide hazard evaluation: a review of current techniques and their application in a multi-scale study, Central Italy

In recent years, growing population and expansion of settlements and life-lines over hazardous areas have largely increased the impact of natural disasters both in industrialized and developing countries. Third world countries have difficulty meeting the high costs of controlling natural hazards through major engineering works and rational land-use planning. Industrialized societies are increasingly reluctant to invest money in structural measures that can reduce natural risks. Hence, the new issue is to implement warning systems and land utilization regulations aimed at minimizing the loss of lives and property without investing in long-term, costly projects of ground stabilization. Government and research institutions worldwide have long attempted to assess landslide hazard and risks and to portray its spatial distribution in maps. Several different methods for assessing landslide hazard were proposed or implemented. The reliability of these maps and the criteria behind these hazard evaluations are ill-formalized or poorly documented. Geomorphological information remains largely descriptive and subjective. It is, hence, somewhat unsuitable to engineers, policy-makers or developers when planning land resources and mitigating the effects of geological hazards. In the Umbria and Marche Regions of Central Italy, attempts at testing the proficiency and limitations of multivariate statistical techniques and of different methodologies for dividing the territory into suitable areas for landslide hazard assessment have been completed, or are in progress, at various scales. These experiments showed that, despite the operational and conceptual limitations, landslide hazard assessment may indeed constitute a suitable, cost-effective aid to land-use planning. Within this framework, engineering geomorphology may play a renewed role in assessing areas at high landslide hazard, and helping mitigate the associated risk.

Landslide Activity Maps for Landslide Hazard Evaluation: Three Case Studies from Southern Italy

This paper focuses on the application of landslideactivity maps for evaluating the mass movementhazard in selected areas of the Southern Apenninesof Italy: Bisaccia, Calitri, and Buoninventre. Theavailability of multi-year aerial photo coveragehelped to assess the morphological changes whichoccurred in the last 40 years. This information,integrated with historical data on slope instabilityand field checks, were used to produce landslideactivity maps. These maps represent a short-cut inthe assessment of mass movement hazard, because theyfocus on the effects of slope instability ratherthan on the causative conditions and processes;however, if kept simple and prepared at large scale,they may help the local administrators and land-useplanners to reduce the socio-economic costs oflandslides. Furthermore, the comparative study oflandslide activity represents a relativelyinexpensive and quick method for evaluating theperformance of the engineering control efforts.The quantification of landslide activity in terms ofareal frequency can represent an additional step,useful to determine the relative landslide hazard(zonation in more or less hazardous areas). Forexample, the estimates of areal frequency of activelandsliding for the last 40 years demonstrated thegreat influence of the 1980 Irpinia earthquake(Ms = 6.9) on the stability of slopes situatedclose to its epicenter (within a radius of about20 km).

Landslide hazard evaluation and zonation mapping in mountainous terrain : Anbalagan, R Engng GeolV32, N4, July 1992, P269–277

Landslide hazard evaluation and zonation mapping in mountainous terrain : Anbalagan, R Engng GeolV32, N4, July 1992, P269–277

Landslide hazard evaluation and zonation mapping in mountainous terrain

Landslide hazard zonation (LHZ) maps are of great help to planners and field engineers for selecting suitable locations to implement development schemes in mountainous terrain, as well as, for adopting appropriate mitigation measures in unstable hazard-prone areas. A new quantitative approach has been evolved, based on major causative factors of slope instability. A case study of landslide hazard zonation in the Himalaya, adopting a landslide- hazard evaluation factor (LHEF) rating scheme, has been presented.

GIS techniques and statistical models in evaluating landslide hazard : Carrara, A; Cardinali, M; Detti, R; Guzetti, F; Pasqui, V; Reichenbach, P Earth Surf Process LandV16, N5, Aug 1991, P427–445

GIS techniques and statistical models in evaluating landslide hazard : Carrara, A; Cardinali, M; Detti, R; Guzetti, F; Pasqui, V; Reichenbach, P Earth Surf Process LandV16, N5, Aug 1991, P427–445

GIS techniques and statistical models in evaluating landslide hazard

AbstractGeographical Information Systems (GIS) and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard.From a small drainage basin located in Central Italy, relevant geological and geomorphological factors were collected and processed by applying GIS technology. In particular, modules were used which both generate high‐fidelity digital terrain models and automatically partition the terrain into main slope‐units. The resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope‐unit. Although not lacking drawbacks, the method proved to be a feasible and cost‐effective approach to landslide susceptibility assessment and mapping.

Landslide analysis concepts for management of forest lands on residual and colluvial soils : Prellwitz, R W; Howard, T R; Wilson, W D Transp Res RecN919, 1983, P27–36

A forest land management analysis scheme is discussed for dealing with landslides that occur in residual and colluvial soils. No one geotechnical or statistical model can be expected to apply to all levels of land management where an assessment of the potential for landslide is vital to a rational decision-making process. The U.S. Department of Agriculture Forest Service in cooperation with the University of Idaho is developing a scheme for evaluating soil-mantle landslide potential to provide information at three levels of land management activities: (a) resource planning; i.e., relative landslide hazard evaluation for resource allocation; (b) project planning; i.e., evaluation of management impacts for comparing alternate transportation routes and timber harvest techniques; and (c) road design and landslide stabilization; i.e., evaluation of alternate road stabilization techniques at a specific critical site. Both geotechnical and statistical analysis techniques are advocated so that the information can be in geotechnical form (factor of safety against failure or critical height of slope) or in statistical form (probability of landslide occurrence) with landslide inventories used as a link between the two. A hypothetical example of the three-level analysis is given. (Author)

Multivariate models for landslide hazard evaluation

As part of a long-term project aimed at a better understanding of the geological and geomorphological factors that control slope instability phenomena in Southern Italy, multivariate models for assessing landslide incidence hazard were developed and tested in two Calabrian sample areas characterized by different geological-geomorphological conditions. Discriminant analysis, based on a large set of mappable geological and geomorphical variables, is able to discriminate rather successfully between stable and unstable areas or slope units. Multiple regression analysis has also proved to be a useful tool in predicting actual and potential landslide hazard. Consequently, geomathematical models may provide a feasible approach to environmental hazard assessment, particularly when applied within the framework of a wider multidisciplinary project for land evaluation and planning.