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Rainfall and landslides: Research into a critical precipitation coefficient in an area of Italy
Abstract
To compare phenomena in environments with similar geomorphologic features but with different rainfall tendency, we can use a precipitation coefficient PC which takes in consideration the daily rainfalls and the recurrent rainfalls obtained by statistical calculations. Landslides that occurred after important rainfalls in the last twenty years are examined in an area of Tuscany (Italy), making a statistical analysis of the rainfalls and computing the Critical Precipitation Coefficient by the above mentioned method. -from Authors
... where CARx n is the calibrated antecedent rainfall for landslidetriggering rainfall event x. The decay constant K, which typically ranges between 0.8 and 0.9, is an empirical value that depends on the drainage capacity of material and the hydrological properties of the area (Capecchi and Focardi 1988). In the current study, K = 0.9 was applied as a good assumption for a maximum of 20 antecedent days, making negligible rainfall occurred more than 20 days before a landslide occurrence after a few tentative trials, as in Marques et al. (2008) and Khan et al. (2012). ...
... The decay constant K = 0.9 derived from a few trials, as in several studies (Marques et al. 2008;Khan et al. 2012), was effectively used for decaying the antecedent rainfall conditions in our study, although this decay constant is not based on the physiographical conditions of South Korea. The constant K, which indicates a soil water recession rate, depends on geomorphic factors such as slope gradient, soil type, and vegetation cover (Glade et al. 2000), and thus on the hydrological characteristics (Capecchi and Focardi 1988) of the area. For this reason, Glade et al. (2000) used the physically derived recession coefficient based on flood hydrographs of each region to produce the antecedent rainfall index in three regions of New Zealand. ...
The intensity-duration (I-D) threshold is considered an effective indicator for landslides triggered by short-term high-intensity rainfall and long-term low-intensity rainfall. However, previous studies have not considered the influence of antecedent rainfall. Herein, we analyzed hourly rainfall data for 613 shallow landslides that occurred from 1963 to 2018 in South Korea to obtain rainfall thresholds and investigated the effect of antecedent rainfall conditions on threshold variations. The I-D and IMAP-D, which is normalized by dividing I by mean annual precipitation (MAP), thresholds were determined to be I = 10.40D–0.31 and IMAP = 0.006D–0.26 (4 ≤ D (h) ≤ 84), respectively, at the 2nd percentile level through quantile regression analysis. These thresholds were lower than other local thresholds (i.e., excluding global and regional thresholds), suggesting that the southern region of the Korean Peninsula was more susceptible to rainfall-induced landslides. Although the effective length of antecedent rainfall was not presented herein, the I-D threshold of landslide-triggering rainfall was confirmed to be low for the absolute and/or calibrated antecedent rainfalls greater than event cumulative rainfall at 5, 7, 10, and 20 days prior to the event. Such differences in I can be greater at shorter durations; however, these differences gradually decrease as D increases, suggesting that they lose their effect as soil water content increases. The results of the current study can improve the understanding of the effect of antecedent rainfall conditions on landslide occurrence and should be further tested with respect to the hydrologic response of hillslopes by considering regional climate and local site conditions.
... where CARx is the calibrated antecedent rainfall for day x; P1 is the daily rainfall for the day before x; Pn is the daily rainfall for the nth day before day x. The constant K is an empirical parameter (typical values range between 0.8 and 0.9) depending on the draining capacity and the hydrological characteristics of the area (Capecchi and Focardi, 1988). After a few tentative trials we have decided to assume in this study that K=0.9, making negligible precipitation occurred more than 30 days before a landslide event (Capecchi and Focardi, 1988). ...
... The constant K is an empirical parameter (typical values range between 0.8 and 0.9) depending on the draining capacity and the hydrological characteristics of the area (Capecchi and Focardi, 1988). After a few tentative trials we have decided to assume in this study that K=0.9, making negligible precipitation occurred more than 30 days before a landslide event (Capecchi and Focardi, 1988). The reconstruction of calibrated antecedent rainfall was performed for time periods of 3, 5, 10, 15 and 30 days. ...
Mt. Bawakaraeng Caldera has been affected by tens of destructive landslide and debris-flow in recent years, triggered by rainfall episodes, which were responsible for many deaths and very important economic losses. Among the instability causes, meteorological factors are of primary importance in the Jeneberan Watershed, South Sulawesi namely the high recurrence rate of rainfall triggering landslides and debris-flow. The cumulative rainfall method is used to reconstruct both absolute and calibrated antecedent rainfall associated with each major landslide and debris-flow event. The critical rainfall combination (amount duration) responsible for each landslide and debris-flow event was assessed and rainfall threshold for land slide and debris-flow was calculated. Rainfall-triggered landslides and debris-flow in the study area are ruled by the function I=86.517Dsup(-0.408), where I is the rainfall intensity in mm/day and D is the duration of rain fall in days. They are related both to short duration precipitation events (1-3 days) with high average, intensity between 82 and 90 mm/day) and long-lasting rainfall episodes (1-5 months) with a lower intensity between 10 and 15 mm/day).
... where CAR x is the calibrated antecedent rainfall for day x; P 1 is the daily rainfall for the day before x; P n is the daily rainfall for the nth day before day x. The constant K is an empirical parameter (typical values range between 0Ð8 and 0Ð9) depending on the draining capacity and the hydrological characteristics of the area (Capecchi and Focardi, 1988). After a few tentative trials we decided to assume in this study that K D 0Ð9, making negligible precipitation occurred more than 30 days before a landslide event (Capecchi and Focardi, 1988). ...
... The constant K is an empirical parameter (typical values range between 0Ð8 and 0Ð9) depending on the draining capacity and the hydrological characteristics of the area (Capecchi and Focardi, 1988). After a few tentative trials we decided to assume in this study that K D 0Ð9, making negligible precipitation occurred more than 30 days before a landslide event (Capecchi and Focardi, 1988). The reconstruction of calibrated antecedent rainfall was performed for time periods of 3, 5, 10, 15 and 30 days. ...
São Miguel Island (Azores) has been affected by hundreds of destructive landslide episodes in the last five centuries, triggered either by earthquakes, volcanic eruptions or rainfall episodes, which were responsible for many deaths and very important economic losses.
Among the instability causes, meteorological factors are of primary importance on Povoação County, namely the high recurrence rate of calamitous rainfall triggering landslides. The most recent catastrophic episode took place on the 31st October 1997 when almost 1000 soil slips and debris flows were triggered, and 29 people died in the Ribeira Quente village.
The role of rainfall on regional landslide activity was analysed applying cumulative rainfall methods. The method comprises the reconstruction of both absolute and calibrated antecedent rainfalls associated with each major landslide event. The critical rainfall combination (amount-duration) responsible for each landslide event was assessed and a rainfall critical threshold for landslide occurrence was calculated. Rainfall-triggered landslides in the study area are ruled by the function I = 144·06 D−0·5551, and they are related both to short duration precipitation events (1–3 days) with high average intensity (between 78 and 144 mm/day) and long-lasting rainfall episodes (1–5 months) with a lower intensity (between 9 and 22 mm/day).
The impact of the North Atlantic Oscillation (NAO) on the regional precipitation regime was evaluated. It is shown that the monthly precipitation of São Miguel is largely modulated by the NAO mode presenting a significant negative correlation with the NAO index. This result arises from the NAO control on the travelling latitude of most storm tracks that cross the Northern Atlantic Ocean. Copyright
... where CARx is the calibrated antecedent rainfall for day x; P 1 is the daily rainfall for the day before day x; P n is the daily rainfall for the n-th day before day x. The constant K is an empirical parameter usually considered between 0.8 and 0.9, depending on the draining capacity of the material and the hydrological characteristics of the area (Capecchi and Focardi, 1988). Following the work developed previously, in the present study it was assumed K=0.9 (Zêzere, 2000). ...
... Following the work developed previously, in the present study it was assumed K=0.9 (Zêzere, 2000). This constant makes rainfall occurring more than 30 days before a landslide event to become negligible (Capecchi and Focardi, 1988). Therefore, the reconstitution of calibrated antecedent rainfall was only performed for durations of 3, 5, 10, 15 and 30 days.Table 3 summarizes results of calibrated antecedent rainfall for both shallow landslide episodes (Table 3a) and deep landslide episodes (Table 3b ). ...
The aim of this study is to assess the impact of the North Atlantic Oscillation (NAO) on both the winter precipitation and the temporal occurrence of different landslide types in Portugal. The analysis is applied to five sample areas located just north of Lisbon, the capital of Portugal. These sites are particularly relevant because actual dates of most of the recent landslide events are known but also because the landslides occurred in a suburban area with growing urbanization pressure.
Results show that the large inter-annual variability of winter precipitation observed in western Iberia, i.e. Portugal and parts of Spain, is largely modulated by the NAO mode. In particular, precipitation falling in Portugal between November and March presents a correlation coefficient of R =–0.66 with the NAO index. Precipitation distribution for the reference rain gauge in the study area reveals that the probability of a wet month to occur is much higher for low NAO index composites than for the corresponding high NAO index composite. It is shown that this control, exerted by NAO on the precipitation regime, is related to corresponding changes in the associated activity of North-Atlantic storm tracks that affect the western Iberia.
Landslide activity in the study area is related to both intense, short duration precipitation events (1–15 days) and long-lasting rainfall episodes (1–3 months). The former events trigger shallow translational slides while the later episodes are usually associated with deeper and larger slope movements. This second group of landslides is shown to be statistically associated with the 3-month average of the NAO index.
... The ancient Silk Road originated in 207 B.C. and has lasted for more than two thousand 38 years serving as a complex network that connects China with the trade centers of the eastern 39 Mediterranean and other regions (Frachetti et al., 2017;Guo, 2018). The Silk Road region 40 covers more than 100 countries that encompass nearly 66% of the world's population (Cui et (Capecchi, 1988). According to the characteristics of the lacks of an effective method for comprehensively combining the spatial distribution of 84 multiple hazards and a well-defined method for determining the boundaries of multiple 85 hazards limit the ability to identify major hazards. ...
Hazard identification is crucial for disaster risk reduction in areas featuring multiple co-occurring hazards and active internal and external dynamic geographical processes. Coupling the elements of external hazard-forming environments and the internal mechanisms inducing hazards, a novel multi-hazard integration zonation (MIZ) method has been developed in which a segmented multi-hazard identification function was constructed to identify the dominant hazard types and their boundaries in a region. Taking the ancient Silk Road as a case study, the major types and spatial zonation of multiple hazards have been identified, which are in accordance with the actual disaster situation. These sympatric multiple hazards present a widely spatial scattered distribution of individual hazards and a more concentrated distribution of multiple hazards in the ancient Silk Road area. These results, combined with the geomorphological features and the climatic zones of the analyzed area, reveal the spatial boundaries among these major hazards at the macro- and microscales. These findings suggest that the proposed MIZ methodology can provide scientific support for rational engineering layouts and regional planning and may serve as pertinent guidance for multi-hazard identification in ancient Silk Road area and beyond.
... The constant K is an empirical parameter that accounts for the decreasing effect of a particular rainy event over time, usually considered between 0.8 and 0.9 depending on the draining capacity of the material and the hydrological characteristics of the area. This constant makes rainfall occurring more than 30 days before a landslide event to become negligible (Capecchi and Focardi, 1988). Therefore, this formula allow considering a maximum of 30-day period of antecedent rainfall. ...
Modeling landslide hazard is among the forecast activities of the Civil Protection system. Usually, scientific literature that aims to determine rainfall thresholds for the possible occurrence of landslides, tends to rely on two main separate approaches: empirical and physical models. This research contributes to such debate by adopting both the approaches, after integrating some of the each other features. This novel methodology has been applied to the landslides affecting the eastward Esino River Valley, located in the Marche region (central Italy). Post-orogenic quaternary sediments, with approximatively similar hydrogeological properties and prone to rainfall-induced shallow landslides, characterize this 550 km2 wide area.
This volume is divided in four sections focusing on: i) the validation of the correlation between historical landslides and rainfall series; ii) the application of empirical models, namely the cumulative event – duration, the maximum intensity – duration, the mean intensity – duration, and the Bayesian methods; iii) the application of the US Geological Survey’s Transient Rainfall Infiltration and Grid-based Regional Slope-stability (TRIGRS) physical model; iv) the testing of all the above models, during a rainfall event that affected the study area on 2-4 May 2014 and triggered several landslides.
Results of this research are proposed as possible decision support tools for landslide warning.
... where CAR x is the calibrated antecedent rainfall for day x, and K is an empirical parameter depending on characteristics of the draining capacity and hydrology of an area (Capecchi and Focardi 1988). In general, the K value ranges between 0.8 and 0.9. ...
Antecedent rainfall plays an important role in rainfall-induced mass movements. However, it is difficult to define the appropriate period of antecedent rainfall for mass movement assessment. To solve this problem, this study provides a simple approach that combines calibrated antecedent rainfall (CAR) and 24-h rainfall for 283 mass movements that occurred in Taiwan from 2006 to 2013. The 24-h rainfall at the time of each mass movement was compared with the total cumulative rainfall for various periods preceding the event. The lowest correlation was found for the total cumulative rainfall from 15 to 20 days before a mass movement day. The 24-h rainfall was compared with the cumulative CAR values for various days of antecedent rainfall. The effect of cumulative CAR on mass movements increased from 22.0 to 39.7% when the number of days considered was increased from 3 to 30 days. However, the increase became gradual after 15–18 days. In addition, the critical antecedent rainfall conditions occurred within 18 days before mass movements in all cases. These results suggest that the antecedent rainfall of 15–18 days is useful for mass movement assessment in Taiwan. This study also established a critical antecedent rainfall threshold for mass movements in Taiwan that is useful for early warnings: Ia = 28.7 D a −1.24 , where Ia is critical mean rainfall intensity during the antecedent rainfall period up to 18 days (mm/day) and Da is the length of the antecedent rainfall period. According to the relationship between 24-h rainfall and the critical antecedent rainfall conditions, low antecedent rainfall intensity that continues for a long time leads to a gradual increase in soil moisture such that a small amount of 24-h rainfall can trigger mass movements. On the other hand, high antecedent rainfall intensity for a short time is not enough to increase soil moisture, and a large amount of 24-h rainfall is needed to flush surface materials and cause mass movements.
... Landslide hazard and susceptibility zonation mapping have been carried out by using various methods and techniques using different scales based on the requirement of the end user and the rationale of the investigation [26]. Different landslide hazards and susceptibility mapping methods described by Mantovani et al. [39] include distribution analysis [16,22,78], qualitative analysis [17,41,43], statistical analysis [53,55,67], deterministic analysis [1,6,44,68], landslide frequency analysis [12,32,40,42], and distribution-free methods such as fuzzy logic [34,36,[52][53][54]69] and artificial neural network (ANN) models [13,15,51,80]. Many researchers adopted the Bureau of Indian Standard [BIS 14496 (Part 2): 1998] guidelines to prepare the landslide hazard zonation mapping [5]. ...
In the present study, the macro landslide hazard zonation (LHZ) mapping and slope stability analyses of selected rock slope (RS) sections were carried out along Kuppanur–Yercaud ghat road section. The macro LHZ map was prepared on 1:50,000 scale using landslide hazard evaluation factor (LHEF) rating scheme proposed by Bureau of Indian Standard IS 14496 (Part-2) 1998. The study incorporated predefined ratings for different
causative factors viz. lithology, structure, slope morphometry, relative relief, land use and land cover, and hydrogeological condition as well as triggering factors like seismicity and rainfall. The total estimated hazard (TEHD) was evaluated by adding ratings of all the causative factors. On the basis of TEHD values, the facet 3 with TEHD value 6.25 was classified as high hazard zone (HHZ). The facet 2 and 4 with TEHD values 5.50 and
5.40 respectively was classified as moderate hazard zones (MHZ). The facet 1 and 5 with TEHD values 2.20 and 3.15 was categorized as very low hazard zone (VLHZ). The slope stability analyses were carried out in six RS sections using rock mass rating (RMR) and slope mass rating (SMR) systems and the factor of safety (FOS) was evaluated for critical discontinuity sets. The results of RMR show that RS sections 1, 2, 4, 5, and 6 fall in
class-III fair rock category, whereas the RS section 3 falls in class-IV poor rock category. The SMR method involves field measurement of slope and discontinuity orientation. These structural values were plotted in the stereonet and identified possible direction and mode of failure. The results of SMR show that the rock sections 1, 2, 4, 5, and 6 falls under partially stable condition, while the rock section 3 comes under unstable
condition. The FOS of the critical discontinuity sections was evaluated for planar as well as wedge failure modes. The results based on planar failure analysis, the RS-2 and RS-3 having FOS < 1 are more unstable for slope failure. The wedge failure analysis shows that all the RS sections having FOS > 1 fall in safe conditions.
... where CARXn is the calibrated antecedent rainfall for day x; P1 is daily rainfall for the day before x; Pn is the daily rainfall for nth day before x. The constant K is an empirical parameter (typical value range between 0.8 and 0.9) depending on the draining capacity and hydrological characteristics of the area (Capecchi and Focardi, 1988). After a few tentative trials we have decided to assume in this study that K= 0.9, making negligible precipitation occurred 30 days before a shallow landslide event. ...
Land cover is an important factor affecting the occurrence of shallow landslides triggered by high intensity rainfall. The objectives of this study are the analyses of the influences of land use and rainfall on shallow landslides using the normalized difference vegetation index (NDVI) and antecedent rainfall threshold. This research was conducted in Tanralili sub-watershed, South Sulawesi Province, Indonesia. The analysis of NDVI using Landsat time series data of 2000, 2003, 2006, 2009, 2011 and 2013. The result indicated that in the course of 14 years high vegetation density land cover (81% to 100%) has lost around 24.21% or 6219 ha. The vegetation density decrease is caused mainly by land use change, especially the conversion of shrubs and forests into mixed dryland farming. 76.67% of shallow landslides occurred are concentrated in mixed dryland farming on the low vegetation density (0 to 40%). The analysis of the absolute and calibrated antecedent rainfall associated with each major shallow landslide event showed that shallow landslides occurred in short duration (1 day) with a high intensity 225 mm/day and longer duration (1 month) with a lower intensity 13 mm/day. The rainfall threshold for shallow landslides in the study area are ruled by the function I = 25.5D-1.10, where I is the average rainfall intensity in mm/day and D is duration of rainfall in days.
... The method of mapping and its scale depends on the necessities of the end user and the purpose of the investigation (Guzzetti et al. 1999). The various landslide susceptibility assessment methods given by Mantovani et al. (1996) include distribution analysis (Wieczorek 1984), qualitative analysis (McKean et al. 1991), statistical analysis Ayalew et al. 2004), deterministic analysis (Mostyn and Fell 1997;Singh et al. 2013;Ahmad et al. 2013), landslide frequency analysis (Capecchi and Focardi 1988), distribution-free methods such as fuzzy logic (Vijith and Madhu 2008;Kanungo et al. 2009;Pradhan et al. 2009;Srivastava et al. 2010;Ramesh and Anbazhagan 2015;Kumar and Anbazhagan 2015;Ramesh et al. 2016), and artificial neural network (ANN) models (Yilmaz 2009;Poudyal et al. 2010;Chauhan et al. 2010;Choi et al. 2012). Many landslide studies have been conducted using probabilistic models such as frequency ratio (Lee and Pradhan 2006;Yilmaz and Keskin 2009;Ehret et al. 2010;Intarawichian and Dasananda 2011;Kannan et al. 2013;Sujatha et al. 2013) and logistic regression (Lee 2005;Akgun and Bulut 2007;Nandi and Shakoor 2008;Tunusluoglu et al. 2008;Sujatha et al. 2011;Xu et al. 2013;Regmi et al. 2014). ...
The hilly region of Manipur especially along the NH-39 road, which is the
lifeline of the State, is prone to landslides every year particularly during the monsoon
season. Anthropological factors, such as excessive deforestation, unsystematic changes in
land use and land cover pattern and slope cultivation, etc. are indirectly initiate the process
of landslides. In the present study, landslide susceptibility mapping was carried out using
frequency ratio and fuzzy gamma operator models with the help of geomatics techniques.
The landslide susceptibility mapping was prepared using landslide inventory data and nine
landslide causative factors, i.e. lithology, land use and land cover, geomorphology, drainage
density, lineament density, slope gradient, slope aspect, curvature, and elevation.
These causative factors were prepared with the help of toposheet, high resolution IRS P6
LISS IV satellite imagery, cartosat DEM data and extensive field work. The landslide
susceptibility maps were prepared by calculating the relationship between the landslide
causative parameters with landslide areas using a frequency ratio model. To get the fuzzy
membership values, the frequency ratio values were normalized between the ranges of 0
and 1. The landslide susceptibility maps were compared and prediction accuracy of both
the models was derived using the area under curve (AUC) method. The success rate curves
were obtained using both training and all landslide inventory dataset. For training landslide
inventory dataset, the AUC value of the success rate curve for the frequency ratio
model was found to be 0.8056, whereas for the fuzzy gamma operator (using c = 0.99)
model, it was calculated as 0.9150. In the case of all landslide inventory dataset, the AUC
value of the success rate curve for the frequency ratio model and the fuzzy gamma operator
model were 0.7921 and 0.8188, respectively. The landslide susceptibility index was also
compared with the landslide validation inventory dataset to obtain the prediction rate
curves. The AUC value of the prediction rate curve for the frequency ratio model was
0.5681, whereas in the case of the fuzzy gamma operator model, it was 0.6721.
... In the eastern area landslides can occur even with small amounts of rainfall because of rather steep terrain. Capecchi & Focardi (1988): The most important cause of the landslide is the pressure exerted by water in the ground. Since the extent of this pressure is regulated by the water which filters in to the soil the landslides due to natural causes usually occur after a period of heavy rainfall. ...
This research focuses on the development of a practical applicable hazard zonation for a 4.43 sq. km large area in the Canton of Lucerne, Switzerland. The area is known to produce significant debris in the main Hohwaeldibach torrent due to large scale mass movements and a significant number of soil slips. The geology of the area consists of flysch (marl, limestone, and claystone), molasse (predominant Hilferen-sandstone, partially with pudding stone layers) and includes a cover layer of colluvium of considerable thickness. In the southern part of the research area, the Northern Helvetic Nappes (limestone, calcarious marl, and sandstone) are outcropping. Small-scale old, as well as fresh sheet and rotational slides, lateral erosion along the channels are main instability indicators and debris producer. Large-scale mass movements of different depth are covering significant parts of the research area and contributing to the accumulation of mobile materials in the torrents. Intensive field work was carried out and various geotechnical site factors were taken into account to analyze the field situation. The collected field data was transferred using Arc View 3.2a to create a landslide inventory map. Large-scale landslides were classified according to their
estimated depth and the estimated long-term mean velocity of the movements. These procedures led to the production of a primary landslide hazard map of the area. Rock fall potential of the areas was marked as per field observation. The final hazard map for the catchment area was then set up. Different re-occurrence periods of extreme events were assumed to estimate hazard and the affected areas were delineated and classified accordingly. With the data collected during field visit, amount of debris, which can be mobilized during heavy-rainfall events, were estimated and one-dimensional simulation was performed to see the effect on alluvial fan downstream.
... 1995). Empirical (Zika et al. 1988) and monitoring revision accepted: 11 March 2009 approaches (Capecchi and Focardi 1988) need continuous long-term information on the landslides and their causal factors for a similar environmental condition or for the same site and these are often not available. The geo-environmental factors which control the stability of slope like lithology, slope morphometry, structure, relative relief, landuse and land cover and hydro-geological condition are generally considered as indexes for parameters included in the safety factor and can be quantified by statistical analysis (Gupta and Joshi 1990, Carrara et al. 1991, Pachauri and Pant 1992, Anbalagan 1992, Jade and Sarkar 1993, Gupta et al. 1993, Naithani et al. 1997, Yin and Yan 1988, Dhakal et al. 1999, Jeganathan and Chauniyal, 2000, Joshi et al. 2003, Sarkar and Gupta 2005, Pachauri 2007, Naithani 2007. ...
Landslide hazard zonation mapping of Tapovan - Helong area of Garhwal Himalaya, where a hydropower scheme of 520 MW is proposed on Dhauli Ganga was carried out. The study area lies in the Main Central Thrust (MCT) zone, which receives majority of the southwest summer Monsoon. The study area belongs to Central Crystalline zone consisting of medium to high grade-quartz-plagioclase-muscovite-biotite-garnet-kyanite and sillimanite bearing crystalline rocks. In the present study statistical analysis of various geo-environmental factors such as the lithology, slope, structure, relative relief, landuse and hydro-geological conditions were used. For preparing the landslide hazard zonation map a quantitative approach called landslide hazard evaluation factors (LHEF) rating has been used. The study indicates that structures, peri-glacial material resting on steeper angle of hill slopes and rainfall plays major role in triggering landslides in this part of the Himalaya. The main aim of this study was to select the best locations for the construction of barrage and sedimentation tank, selections of sites for the tunnels portal and the switchyard area and finally appropriate slope stabilization measures were also suggested. The study further suggests that in the investigation stage for river valley projects, landslide hazard evaluation factor (LHEF) rating scheme can provide rapid hazard assessment in a mountainous terrain.
... In addition to the previous methods, landslide frequency analysis methods have also been reported for site specific studies on landslides. These are indirect methods in which earthquakes and/or rainfall records or hydrological models are used for correlation with known landslide dates to obtain threshold values with a certain frequency (Capecchi and Forcardi, 1988;Jibson et al., 1998). ...
Among the various natural hazards, mass movements (MM) are probably the most damaging to the natural and human environment in the Mediterranean countries, including Lebanon which represents a good case study of mountainous landscape. Although affecting vast areas in the country, the phenomenon was not studied at regional scale, and related maps are still lacking. Therefore, this research deals with the use of remote sensing and geographic information system (GIS) techniques in studying MM in Lebanon. In this context, the first part reviews existing knowledge on the topics of mass movements (MM) specifically in the Mediterranean region, and defines research gaps. It exposes the diverse types of MM, their magnitudes, the causative agents and their bad consequences. It clarifies confusions related to MM-terms (hazard, susceptibility, risk, etc.), and compares the efficiencies of the most used methods for MM susceptibility/hazard zonation. It includes also a statement on remote sensing and GIS benefits and constraints in mass movement studies, pointing out possible ways of research. The second part is dedicated to the detailed description of the study area "the Mediteranean slopes of central to north Lebanon" within Lebanon. Physical/morphodynamic and socioeconomic characteristics of the area are exposed, as well as the natural hazards, MM events, their socio-economic impacts and mitigation measures. All previous studies about MM hazard in Lebanon are reviewed. The studied area, extending from the Mediterranean coast to around 3000 m elevation, covers ~36% of the total area of Lebanon. It represents the geoenvironmental diversity of this country in terms of geology, soil, hydrography, land cover and climate. It is characterized by problematic human activities (e.g., chaotic urban expansion, artificial recharge of groundwater, overgrazing, forest fire) enhancing environmental decline and inducing MM, with minimal government control. The third part compares the applicability of different satellite sensors (Landsat TM, IRS, SPOT4) and preferred image processing techniques (False Color Composite "FCC", Pansharpen, Principal component analysis "PCA", Anaglyph) for the mapping of MM recognized as landslides, rock/debris falls and earth flows. Results from the imagery have been validated by field surveys and analysis of IKONOS imagery (1 m) acquired in some locations witnessing major MM during long periods. Then, levels of accuracies of detected MM from satellite imageries were plotted. This study has demonstrated that the anaglyph produced from the two panchromatic stereo-pairs SPOT4 images remains the most effective tool setting the needed 3-D properties for visual interpretation and showing maximum accuracy of 69%. The PCA pan-sharpen Landsat TM-IRS image gave better results in detecting MM, among other processing techniques, with maximum accuracy level of 62%. The errors in interpretation fluctuate not only according to the processing technique, but also due to the difference in MM type. They are minimal once 3D anaglyph SPOT4 is considered, varying between 31% (landslides), 36% (rock and debris falls) and reaching 46% in the case of earth and debris flows. The fourth part explores relationships between MM occurrence and different factor terrain parameters. Parameters expressed by: 1- preconditioning factors, like: elevation, slope gradient, slope aspect, slope curvature, lithology, proximity to fault line, karst type, distance to quarries, soil type, distance to drainage line, distance to water sources, land cover/use, and proximity to roads, and 2- triggering MM factors, like: rainfall quantity, seismic events,floods and forest fires, were correlated with MM using GIS-approaches. This study indicates, depending on bivariate remote sensing and GIS statistical correlations (Kendall Tau-b correlation), that lithology is the most influencing on MM occurrence, having the highest correlation with other parameters (i.e. 7 times correlated at 1% level of significance and 3 times at 5%). It also shows that statistical correlations to mass movements exist best between parameters at the following decreasing order of importance: soil type/distance to water sources (acting similarly on MM occurrence), karst/distance to quarries/land cover-use, proximity to faults, slope gradient/proximity to roads/floods, seismic events, elevation/slope aspect/forest fires. These correlations were verified and checked through field observations and explained using univariate statistical correlations. Therefore, they could be extrapolated to other Mediterranean countries having similar geoenvironmental conditions. The fifth part proposes a mathematical decision making method - Valuing Analytical Bi- Univariate (VABU) that considers two-level weights for mapping MM susceptibility/hazard (1:50,000 cartographic scale) within the study area. The reliability of this method is examined through field surveys and depending on a GIS comparison with other statistical methods - Valuing accumulation Area (VAA) (depending on one weight level) and Information Value (InfoVal) (requiring detailed measurements of MM areas). Three susceptibility maps were derived using preconditioning parameters, while hazard maps were produced from triggering ones. The coincidence values of overlapping susceptibility maps were found to be equal to 47.5% (VABU/VAA), 54% (VABU/InfoVal) and 38% (VAA/InfoVal). The agreement between hazard maps showed closer values than susceptibility ones, oscillating between 36.5% (VAA/InfoVal), 39% (VABU/VAA), and 44 % (VABU/InfoVal). Field verification indicates that the total precision of the produced susceptibility maps ranges from 52.5% (VAA method), 67.5% (InfoVal method) and 77.5% (VABU method). This demonstrates the efficiency of our method, which consequently can be adopted for predictive mapping of MM susceptibility/hazard in other areas in Lebanon and may be easily extrapolated using the functional capacities of GIS. The sixth part predicts the geographic distribution and volume of block falls (m3) across the study area using GIS decision-tree modelling. Such mapping was unavailable in Lebanon, but also in many other countries putting effort on landslide research rather than other types of MM. Several decision-tree models were developed using (1) all terrain parameters, (2) topographic parameters only, (3) geologic parameters only, and adopting various processing techniques (pruned and unpruned trees). The best regression tree model combined all parameters and explained 80% of the variability in field blocks falls' measurements. The unpruned model built using four geological parameters (lithology, soil type, proximity to fault line, and karst type) seems also interesting, classifying 68% of block falls and referring to a small amount of input data (4 parameters). The produced predictive quantitative block falls' map at 1:50,000 appears extremely useful for decision-making, helping adoption of mitigation measures to reduce the occurrence of harmful block falls. The seventh part focuses on monitoring MM activity through integrating space borne radar data and Global Positioning System (GPS) techniques. ERS radar imageries were processed using InSAR and permanent scatters techniques. The analysis showed difficulties in detecting ground deformations due to MM. Nevertheless, the analysis is still in its preliminary stage and future planned work will take into consideration other manipulating procedures for detecting the displacements. On the other hand, a GPS installation in Hammana area; one of the Lebanese villages lying in a major landslide, was conducted. Two campaigns were raised, but results are still lacking since there is not enough data accumulation. More observations are still needed to build up a comprehensive picture on the direction and velocity of the movement.
... The methods of landslide hazard and susceptibility assessment techniques by Mantovani et al. (1996) includes distribution analysis (Wieczorek 1984), qualitative analysis (Kienholz et al. 1984;McKean et al. 1991), statistical analysis (Yin and Yan 1988;Gupta and Joshi 1990;Carrara et al. 1991;Wang and Unwin 1992;Pachauri and Pant 1992;Sarkar et al. 1995;Mark and Ellen 1995;Chung and Fabbri 1999;Lee et al. 2002;Ayalew et al. 2004), deterministic analysis (Skempton and Delory 1957;Okimura 1982;Okimura and Kawatani 1986;Mostyn and Fell 1997;Singh et al. 2013a, b;Ahmad et al. 2013), landslide frequency analysis (Capecchi and Focardi 1988), and distribution-free methods such as fuzzy and ANN. Several studies have been carried out for estimating the spatial probability of landslide occurrences using GIS technique. ...
This article emphasizes landslide susceptibility mapping along Ghat road of Kolli hills, Tamil Nadu, India, using frequency ratio, relative effect and fuzzy gamma operator models with the help of remote sensing data and GIS technique. The purpose of the study is to generate, compare and validate landslide susceptibility zones. Landslide inventory was done with data collected from the State Highways department. There are nine landslide-influencing parameters such as slope gradient, slope aspect, slope curvature, relief, lithology, land use and land cover, proximity to road, proximity to drainage, and proximity to lineament, analyzed with help of topo map, existing geology map and satellite data to produce landslide susceptibility maps. Landslide susceptibility maps were generated by calculating relationship between the landslide-influencing factors with past landslide locations using frequency ratio, relative effect and fuzzy gamma operator models. These landslide susceptibility maps were verified and compared using the existing landslide inventory data. The prediction accuracy of frequency ratio model was 87.93 %, for fuzzy gamma operator model was 87.33 %, and for relative effect model it was 85.26 %. Out of which, the frequency ratio model provide maximum prediction accuracy on landslide susceptibility.
... where CAR x is calibrated antecedent rainfall for day x; K is an empirical (constant) parameter that depends on the draining capacity and hydrological properties of the study area (Capecchi and Focardi 1988). Generally, K ranges from a value between 0.8 and 0.9. ...
The major landslide events that occurred in Chittagong City in 2007 and 2008 have caused the death of about 140 people and incurred a considerable amount of property loss. At least ten landslide events occurred during the period of 2000–2009, with mainly rainfall as the triggering factor. The critical rainfall condition of the landslide events was analyzed with Gumbel’s extreme value distribution using the historical rainfall–landslide data. The antecedent rainfalls were used for Gumbel’s distribution for the critical rainfall intensity–durations of each historical landslide event. Landslides were correlated with the monthly average as well as the percentile rank of monthly median rainfall. The regression relationship between 30 days of absolute antecedent rainfall intensity (I) and corresponding duration (D) of rainfall responsible for the landslides in the study area was found as I = −15.8ln(D) + 60.49. The calibrated antecedent rainfall analysis showed a relation between I and D as I = −40.5ln(D) + 162.5. The major recent landslide events were related to the extreme rainfall intensities (>40 mm/day) having short period of time (2–7 days). All the major landslide events occurred at much higher rainfall amount compared to the monthly average. However, these rainfall thresholds were statistically based and were not defined hydrological response of rainfall to the soil, as well as other geological conditions associated with slopes.
... Thus the frequency distributions of the rainfall threshold in landsliding areas need to be exploited to provide a hazards assessment tool in order to foresee and prevent the landslide risk. These insights into landslides within sediments with medium-low permeability constitute a working hypothesis in which long time series of cumulated rains are evaluated (Galliani et al. 2001, Santaloia et al. 2001, Polemio & Sdao 1999, Pasuto & Silvano 1998, Wasowski 1998, Parise et al. 1997, D'Ecclesis et al. 1991, Capecchi et al. 1988, Cascini & Versace 1988, 1986, Canuti et al. 1985, Govi et al. 1985). To define the " threshold value " of landslide events there is a clear need for a better understanding of the spatial distribution in deposits characterized by medium-high permeability of the shallow landslides induced by extreme and small rain events (Belloni & Martini 1997, Mortara et al. 1994, Cannon & Ellen 1988, Wieczorek & Sarmento 1988, Keefer et al. 1987, Wieczorek 1987, Cancelli & Nova 1985, Moser & Hohensin 1983, Govi & Soriana 1980, Caine, 1980). ...
Most of the important historical towns in Umbria are built on Plio-Pleistocene sediments. This lithological complex is affected by landslide hazard (earth slides and earth slumps) as a consequence of its geological structure, in particular where clays percentage is significant. Rainfalls prolonged over time are studied to detect the minimum amounts necessary for generating critical conditions in the subsoil.
... Shallow, rapid landslides typically occur on steep slopes and are often triggered by individual rainstorm events (O'Loughlin et al., 1982;Sidle and Swanston, 1982;Tsukamoto et al., 1982). Rainstorm characteristics that have been empirically related to shallow groundwater response and associated landslide occurrence include storm mean and maximum hourly intensity, storm duration, rainfall amount, and antecedent rainfall (Caine, 1980;Sidle and Swanston, 1982;Sidle 1984aSidle , 1986Canuti et al., 1985;Wieczorek, 1987;Capecchi and Focardi, 1988;Dhakal, 1995;Finlay et al., 1997). During such major rainstorms the pore water pressure builds up in the soil mantle, usually just above the lithic contact or other hydrologic impeding layer (e.g. ...
A physically based distributed slope stability model is described that utilizes a combined surface–subsurface kinematic wave module to assess groundwater fluctuations related to slope stability. A total of 82 major rainstorms from 1972 to 1990 in Carnation Creek, British Columbia, were examined to determine the influence of different characteristics of rainstorms (such as mean and maximum hourly intensity, duration, and rainfall amount) on the slope stability. These rainstorms vary in mean intensity from 1·6 to 11·2 mm h−1, storm duration from 11 to 93 h, and maximum hourly intensity from 3·4 to 35 mm h−1. Four synthetic ‘uniform intensity’ rainstorms were also tested against real storms to assess the effect of short‐term hourly rainfall intensity peaks on landslide occurrence. Altogether, 602 simulations were conducted. The combined influence of mean and maximum hourly intensity, duration, and total rainfall amount of rainstorms were important in generating landslides. The temporal distribution of short‐term intensity also influenced the landslide occurrence. When saturated hydraulic conductivity of the soil was lowered or soil depth was raised, most rainstorms produced larger numbers of landslides. For the most part, actual rainstorms produced less stable conditions than their synthetic ‘uniform intensity’ counterparts. For all landslide‐producing storms, slope failure usually occurred after some threshold of cumulative rainfall and maximum hourly rainfall intensity. These simulations provide insights into the distributed behaviour of landslide occurrence during large rainstorms with varying characteristics. Copyright © 2004 John Wiley & Sons, Ltd.
... , 1987a ; Tatizana et al . , 1987b ; Capecchi e Focardi , 1988 ; Almeida e Nakazawa , 1991 ; Pedrosa , 1994 ; D ' Órsi et al . , 1997 ) . ...
Deslizamentos são episódios de extrema importância, resultantes da atuação de processos geomorfológicos nas mais diversas escalas temporais causando, em geral, enormes prejuízos à sociedade. Dentre os diversos fatores condicionantes destacam-se os parâmetros morfológicos do terreno, os quais controlam diretamente o equilíbrio das forças e, indiretamente, a dinâmica hidrológica dos solos. Embora muitos estudos tenham voltado a atenção para a descrição de eventos e para o monitoramento de campo, pouco ainda se sabe sobre a previsão de ocorrência destes fenômenos. Acredita-se aqui que a combinação de mapeamentos e monitoramentos de campo, através de modelos matemáticos baseados em processos, tenha muito a contribuir nessa direção. Neste sentido, diversos estudos de campo vêm sendo realizados nas bacias dos rios Quitite e Papagaio no sentido de caracterizar o papel desempenhado pelos diversos parâmetros topográficos no condicionamento dos deslizamentos ali ocorridos em 1996. A partir do modelo digital de terreno das bacias, com uma resolução de 4m2, combinado com vários mapeamentos ali realizados, foi definido o potencial de deslizamento para as diversas classes de cada atributo topográfico. Paralelamente, foram realizados ensaios de campo com o permeâmetro de Guelph e simulações com o modelo matemático SHALSTAB, voltado para a previsão de áreas instáveis, de modo a englobar os mais diferentes cenários. Os resultados atestam o importante papel desempenhado pelos parâmetros topográficos forma da encosta e área de contribuição, geralmente desprezados pelas metodologias de previsão de áreas susceptíveis a deslizamentos.
... Neural networks and neuro-fuzzy methods, which do not depend on distributional assumptions of the data. Here, the weights are computed in an objective manner Arora et al. (2004), Elias and Bandis (2000) 5. Deterministic analysis Indirect methods in which parameters are combined in slope stability calculation Okimura and Kawatani (1986) 6. Landslide frequency analysis Indirect methods in which earthquakes and/or rainfall records or hydrological models are used for correlation with known landslide dates to obtain threshold values with a certain frequency Capecchi and Focardi (1988) Data layer preparation A number of thematic maps (referred to as data layers in GIS) on specific factors or parameters related to the occurrence of landslides, viz. slope, aspect, relative relief, tectonic structures, lithology, landcover and drainage density have been generated. ...
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.
... Therefore, landslide prediction is closely related to the probability of exceeding given precipitation threshold values. There is a vast body of literature on this topic, which has yielded important results in the past two decades (e.g., Keefer et al., 1987;Cannon, 1988;Capecchi and Focardi, 1988;Finlay et al., 1997;Au, 1998;Glade, 1998;Reichenbach et al., 1998;Domínguez Cuesta et al., 1999;Polemio and Sdao, 1999;Chleborad, 2000;Waltham and Dixon, 2000;Dai and Lee, 2001;Ibsen and Casagli, 2004;Luino, 2005;Claessens et al., 2006). ...
This study proposes a modification of the conventional threshold model for assessing the probability of rainfall-induced landslide reactivation. The modification is based on the consideration that exceedance of a pre-determined rainfall threshold is a necessary but not sufficient condition to reactivate a landslide. The proposed method calculates the probability of reactivation as a function of the probability of exceedance of a pre-determined rainfall threshold, as well as the probability of occurrence of a landslide after such exceedance. The data for the calculation were obtained from historical records of landslides and rainfall.
... Because of the high permeability of the Campania pyroclastic cover and the steep hill slopes, positive pore pressure would rapidly decrease after each storm. For other areas (Capecchi and Focardi, 1988;Crozier, 1999;Wilson and Wiezoreck, 1995), this decrease has been proposed to be approximated analytically with an exponential time function. ...
A combination of empirical and physically based hydrological models has been used to analyze historical data on rainfall and debris-flow occurrence in western Campania, to examine the correlation between rainfall and debris-flow events.Rainfall data from major storms recorded in recent decades in western Campania were compiled, including daily series from several rain gauges located inside landslide areas, supplemented by hourly rainfall data from some of the principal storms.A two-phase approach is proposed. During phase 1, soil moisture levels have been modelled as the hydrological balance between precipitation and evapotranspiration, on a daily scale, using the method of Thornthwaite [Geograph. Rev. 38 (1948) 55].Phase 2 is related to the accumulation of surplus moisture from intense rainfall, leading to the development of positive pore pressures. These interactions take place on an hourly time scale by the “leaky barrel” (LB) model described by Wilson and Wiezoreck [Env. Eng. Geoscience, 1 (1995) 11]. In combination with hourly rainfall records, the LB model has been used to compare hydrological effects of different storms. The critical level of retained rain water has been fixed by the timing of debris-flow activity, related to recorded storm events.New rainfall intensity–duration thresholds for debris-flow initiation in western Campania are proposed. These thresholds are related to individual rain gauge and assume a previously satisfied field capacity condition. The new thresholds are somewhat higher than those plotted by previous authors, but are thought to be more accurate and thus need less conservatism.
... The precipitation coefficient of Canuti et al. (1985) was taken into consideration for assessing the role of the climate in promoting shallow landslides. The original formula was, however, modified by removing the normalization factor from Eq. (2) and by giving to the k parameter a constant value of 0.9, which is suitable for fragmented sandstone rocks with high water conductivity (Capecchi and Focardi, 1988; Focardi, 1988). Thus, Eq. (2) becomes PC n ¼ X n i¼1 ...
A pluviometrical data analysis was carried out for 292 Italian weather stations in order to identify an index able to classify the climatic aggressiveness with respect to some instability phenomena (quick flows, soil erosion and shallow landslides). Several climatic variables were calculated such as the average annual rainfall, the two-year return time maximum rainfall amount for 6-, 24-h, 1-, 5-day and monthly durations, the occurrence probabilities of potentially erosive phenomena, Canuti’s precipitation coefficient relative to landslide triggering and the Fournier index calculated either in the original form or with the modification proposed by Arnoldus. The latter was elaborated from the mean monthly rainfalls over the whole observation period (MFI) and as average of the individual indices calculated from the monthly dataset of each year (MFIavg). The study of the relationships among the analyzed quantities outlined the high versatility of Fournier index, particularly the modified form, which appeared closely related to all the investigated variables; therefore it may be used as a suitable synthetic way to describe different features of the pluviometric regime of a given location. A classification framework based on two threshold values of MFIavg and of the corresponding MFI is also proposed.
... In this case the significant effect of no recent rainfall was reasonably linked to the groundwater recharge of the landslide body. Moreover, decay factors were successfully used when a single type of phenomenon involved homogenous lithological areas, as is the case for the landslides described by Capecchi and Focardi (1988) . The use of decay factors is extremely complex wherever various lithologies are involved, as was shown in a study on landslides of a wide region in which Avigliano is located (Naden et al., 1993 ). ...
Landslides, floods and secondary floods (hereinafter called phenomena) triggered by rainfall and causing extensive damage are reviewed in this paper. Damaging Hydrogeological Events (DHEs) are defined as the occurrence of one or more simultaneous aforementioned phenomena. A method for the characterisation of DHEs based upon historic data is proposed. The method is aimed at assessing DHE-related hazard in terms of recurrence, severity, damage, and extent of the affected area. Using GIS, the DHEs historical and climatic data collection, the geomorphological and hydrogeological characterisation of the hit areas, the characterisation of induced damage, the evaluation of triggering rainfall return period and critical duration of each DHE were carried out. The approach was applied to a test site in Southern Italy (Calabria) for validation purposes. A database was set up including data from 24 events which have occurred during an 80-year period. The spatial distribution of phenomena was analysed together with the return period of cumulative rainfall. The trend of the occurred phenomena was also compared with the climatic trend. Four main types of Damaging Hydrogeological Events were identified in the study area. Published 17-30 JCR Journal
Moisture-driven landslides (MDL), mainly caused by rain, seriously threaten lives and property, resulting in catastrophic damages and considerable economic losses. In areas with steep topography, the temporal and spatial clustering of long-duration, moderate-to-short-duration high-intensity rainfall contributes to landslides. Shifting precipitation patterns due to climate change, alterations to sub-surface conditions, such as pore-water pressures, retreating glaciers, and permafrost, further increase the risk of landslides. This synthesis apprises the physical drivers associated with MDLs and their complex interplay in triggering MDLs. The added value of this synthesis is multifaceted: (1) to uncover moisture-driven landslide trends and associated cascading hazards across the high-mountain areas of the globe (2) To explore the probability of rain-driven landslide-related mortality rate across different continents using the archived landslide information. (3) To present a systematic review of available physical and statistical tools to identify MDL triggers and highlight the need for updating rain thresholds using observed and projected climate information to address nonstationarities related to climate change and climate variability. Our analysis of archived rainfall-triggered landslides of the global landslide catalogue between 2007 and 2022 shows that global precipitation contributes to more than 60% of landslides. Further, our observational assessments of the fatality versus landslide frequency curves show that high-mountain Asia experiences the most frequent landslides, and its populations are especially vulnerable to such catastrophic events. The contribution of this synthesis paper is to inform scientists and practitioners of the latest developments in MDLs, aiding the translation of scientific understanding into developing resilience policies and adaptation efforts.
Aerial photographs and GIS were applied for assessing landslide hazard, producing landslide hazard maps, and evaluating these maps, in the Kulekhani watershed (124 km²), located in the central region of Nepal. A landslide distribution map was produced from aerial photo interpretation and field checking. Eight factors, slope gradient, slope aspect, elevation, drainage basin order, distance from ridge, distance from valley, geology, and land use/cover, were analyzed by a multivariate statistical (discriminant) method, to determine the factors and classes influencing landsliding. Using a GIS, three different sets of samples from non-landslide group, and one set of samples from landslide group were generated from the unaligned stratified random and simple random sampling methods, respectively. Three different combinations were then used to examine the effects of the sampling methods on the critical factors and classes, and on the hazard maps produced from the results of the analysis. Each hazard map was produced with four levels of hazard classes: high; moderate; less; and least. The geology was found to be the most important factor to landsliding. Other important factors include elevation, land use/cover and slope aspect. Combinations of different samples did not yield substantial difference in the critical factors and classes, implying that the unaligned stratified random sampling is the appropriate sampling technique for generating the non-landslide group. The accuracies of three hazard maps were found to be acceptable for their practical use in hazard mitigation and watershed management planning.
A study is presented of the application of GIS to landslide hazard mapping. Two methods of statistical analysis are employed: the failure rate (FR) and quantification scaling type II (Q-S II). The study area is the Kulekhani watershed $(124\ {\rm km}^{2})$ , located in central Nepal. A map showing the distribution of landslides was produced from air photograph interpretation and field checking. This was used to analyze the important terrain factors influencing landslide initiation. The factors employed were slope gradient, slope aspect, elevation, geology, land-use/cover, proximity to fault lines, and drainage density. Each factor was divided into several classes. The influencing factors were first determined from the FR analysis and were then considered for the Q-S II analysis. Also, two of the influencing factors were overlaid in turn to produce combined-factor layers (consisting of combined-classes). This was used as the basis for another FR analysis. Geology was found to be the most important factor influencing landslide activity. Other important factors were elevation and land use/cover. Based on the results of the three analyses, three hazard maps were produced each with four levels of hazard classes: high; moderate; less; and least. The area occupied by the different hazard classes do not show substantial variation from map to map. In general, about four percent of the study area fell into the "high hazard class." The "moderate," "less," and "least" hazard classes occupied about a quarter, a half, and a fifth of the total study area, respectively.
The literature contains many examples, which demonstrates the importance of climatic conditions, particularly of rainfall but also temperature, on landslide activation. Normally landslides occur during specific hydrologic conditions; the relative importance of each factor will however vary with the landslide type.
Heavy rains are one of the main natural factors producing landslides as they may cause pore pressure to increase on slopes or can create adverse seepage conditions, modify the slope's geometry as a result of erosion and originate swelling and softening processes in clay soils.
According to their different behaviour, it is necessary to distinguish shallow or deep-seated landslides, first-time or reactivated landslides, the nature of landslide body (terrain or rock) as well as the hydrogeological nature of soils.
Shallow landslides in soils and weathered rocks are often generated on steep slopes during the most intense part of a storm (lasting from minutes to several hours). The higher permeability of the outermost portion of the slope, compared to the bedrock below, allows for the creation of a temporary perched water-table, inducing the progressive increase of pore-water pressure.
On the other hand, deep-seated landslides can be mobilised as a consequence of moderate intensity rainfalls lasting several days, owing to the longer recharging time required for ground-water level to rise and cause a significant build up in pore-water pressure.
Pioneer studies, concerning landslides triggered by rainfalls, go back to '30s. Were selected 138 papers and key information was collected in a database. Nearly 82 % of all records are local investigations carried out in 23 countries. Italy provides the largest sample as for author’s nationality and widespread proneness to landslides; followed by United States (15 %), Hong Kong (8 %), Japan and United Kingdom.
Two main approaches have been used to investigate rainfall-induced landslides:
-empirical or semi-empirical relationships, using statistical correlation and forecasting techniques;
-deterministic modelling of groundwater recharge and pore-water pressure changes.
Studies concerning the first type of approach have reached interesting results about combination of antecedent rainfall and rainstorms intensity able to trigger widespread soilslip activation in specific geological, morphological and climatic settings.
Relationships between rainfall intensities and duration associated with shallow landslides and debris flows activation has also been found and they are often used for warning purposes.
For the activation of widespread mass movements, some authors underline the role of an effective rainfall period ended by a pronounced increased of rainfall intensity; in this situations hazard precursors may be considered as a combination of cumulate rainfall and rainfall intensity.
The second approach requires the development of a clear picture of the modes of water flow on and below the ground surface: where groundwater flow is concerned, attention is focused on both the saturated and the unsaturated zones and complete hydrological models of slopes must be defined.
The present paper is a critical overview of recent international research activity on this subject. Methods and experiences are compared and classified. Some author's direct experiences are utilised for these purposes.
The Mediterranean has been subject to changing human settlement and land use patterns for millennia, and has a history of human exploitation in an inherently unstable landscape. Environmental Issues in the Mediterranean reviews both physical and social aspects of this region, in relation to its environment. Ideal for students who are studying a range of environmental issues, but want to see them linked within one regional context. The book begins with an introduction to the Mediterranean region, its history, physical and human geography and its environmental problems. It then goes on to examine: The Dynamic Environment - climate variables and fluctuations, vegetation, the hydrological cycle of the basin and its watershed, processes of erosion, fire and the Mediterranean Sea. The Human Impact on the Environment - prehistoric and historic land use, traditional agriculture, rural and urban settlement and use of mineral resources. The Mediterranean Environment Under Increasing Pressure - the present human landscape, changes in agriculture in the 20th century, the impact of depopulation, pollution, water resources, desertification and potential climatic change. It then concludes with a discussion of the region's on-going environmental issues of water resources, land degradation, agricultural intensification and tourism, and considers how these can be approached using management techniques and national and regional policies. © 2004 John Wainwright and John B. Thornes. All rights reserved.
A distributed shallow groundwater model related to slope stability is described to assess the spatial distribution of pore water pressure in steep forested terrain in British Columbia. Additionally, effects of timber harvesting and roads on measured changes in pressure head during rainstorms were evaluated for the first time to assess the need for incorporating different hydrological components in the event-driven distributed model. Although explicit spatial quantification of pore water pressure requires many measurements for accurate prediction, model performance using average parameter values was reasonable when compared with pressure heads measured at nine spatially distributed sites. Increases in maximum pressure head (varying from 9 to 28 cm) between preharvesting (after road construction) and postharvesting rainstorm events were observed in seven of nine sites. The remaining two sites showed either a small decrease (~5 cm) or similar peak pressure heads following harvesting. Peak pressure head evaluated at one piezometer located 46 m downslope of the road decreased substantially (~50 cm) after road construction during moderate rainstorms and then recovered following harvesting. Piezometric responses in sites upslope of the road were not affected by road construction but did increase after harvesting. Moderate storms caused the largest relative increases in pressure head between preharvesting (after roads) and postharvesting conditions; such increases were small during large storms, lending support to the idea that timber harvesting in temperate forests enhances hydrologic response only during small and moderate storms. Since landslides in coastal Pacific Northwest are typically caused by large winter rainstorms, it appears more justified to include better spatial representation of soil physical and engineering parameters in the distributed shallow groundwater model compared to specifying evapotranspiration; road hydrology may, however, need to be included.
Rainfall is the most common cause of landslides. The cost of Rainfall Triggered Landslides (RTL) is not well documented and often unobtainable. In areas where they do not pose a threat to life, great damage is caused to farmland and communication infrastructures and pasture bio-mass production is heavily reduced (Table 1). In Japan more than 10,000 RTL are reported every year which claim the lives of some 400 persons (Fukuoka, 1980); A single event has killed 100 persons and inflicted property damages estimated at 300 billion yen Shimizu (1988).
Given the importance of the topic, some 138 papers dealing with RTL were selected and key information was collected in a database. Nearly 82 % of all records are local investigations carried out in 23 countries. Italy provides the largest sample as for authors' nationality and widespread proneness to landslides; followed by United States (15 %), Hong Kong (8 %), Japan and United Kingdom. About 21 % of all selected papers are methodological research or syntheses and comparisons of different methodologies. Investigations refer to widespread landsliding (69 % of AD) (that is the Available Data number for each database field), the remainder corresponds to single or few landslides. A landslide classification proposed by Hutchinsons (1995) and based on the maximum depth of failure (Vm), is adopted in this work. About 40 % of AD are intermediate or deep-seated landslides (Vm > 10 m), that include all reactivations, the rest are shallow or superficial landslides, generally first-time movements. The most frequent types are: flows, translational and rotational slides, slips, avalanches and creep, decreasing order (Cruden & Varnes 1996) with soil or debris generally constituting the landslide bodies. Daily (54 % of AD), hourly (28 %), monthly (15 %) and yearly (4 %) rainfalls are used as input. Roughly 49 % consider cumulative rainfall (a rain water height obtained adding regularly monitored rainfall) of different duration. The prevalent approach is empirical, statistical or hydrological-qualitative; one out of four is partially physical and often uses numerical modelling. About 10 % combine rainfall effect characterisation with geotechnical stability analysis. The results of research in progress have been summarised.
The distribution of slide rate in time and space in an active landslide in varved clays in the French Alps are presented. Convergent flow of the sliding mass and increase of slide rate downslope appeared from geodetic measurements. By means of a mass balance it is shown that the convergence is compensated by the increased slide rate hence the depth of the sliding mass is constant throughout the slide. In the eight years of recording, variations in the precipitation totals in the period accumulated masses forms an additional explanation.
On February 6, 1994, a large debris flow developed because of intense rains in a 800-m-high mountain range called Serra do
Cubatão, the local name for the Serra do Mar, located along the coast of the state of São Paulo, Brazil. It affected the Presidente
Bernardes Refinery, owned by Petrobrás, in Cubatão. The damages amounted to about US 40 million because of the muck cleaning, repairs, and 3-week interruption of the operations. This prompted Petrobrás to conduct studies, carried out by the authors, to develop protection works, which were done at a cost of approximately US40 million because of the muck cleaning,
repairs, and 3-week interruption of the operations. This prompted Petrobrás to conduct studies, carried out by the authors,
to develop protection works, which were done at a cost of approximately US 12 million. The paper describes the studies conducted
on debris flow mechanics. A new criteria to define rainfall intensities that trigger debris flows is presented, as well as
a correlation of slipped area with soil porosity and rain intensity. Also presented are (a) an actual grain size distribution
of a deposited material, determined by laboratory and a large-scale field test, and (b) the size distribution of large boulders
along the river bed. Based on theory, empirical experience and back-analysis of the events, the main parameters as the front
velocity, the peak discharge and the volume of the transported sediments were determined in a rational basis for the design
of the protection works. Finally, the paper describes the set of the protection works built, emphasizing their concept and
function. They also included some low-cost innovative works.
Mass movements varying in type and size, some of which are periodically reactivated, affect the urban area of Avigliano. The disturbed and remoulded masses consist of sandy–silty or silty–clayey plastic material interbedded with stone fragments and conglomerate blocks. Five landslides that were markedly liable to rainfall-associated instability phenomena were selected.The relationships between landslides and rainfall were investigated using a hydrological and statistical model based on long-term series of daily rainfall data. The model was used to determine the return period of cumulative daily rainfall over 1–180 days. The resulting hydrological and statistical findings are discussed with the aim of identifying the rainfall duration most critical to landslides.The concept of a precipitation threshold was generalized by defining some probability classes of cumulative rainfall. These classes indicate the thresholds beyond which reactivation is likely to occur. The probability classes are defined according to the return period of the cumulative rainfall concomitant with landslide reactivation.
An inventory is presented of researches concerning the use of remote sensing for landslide studies and hazard zonation as mainly carried out in the countries belonging to the European Community. An overview is given of the applicability of remote sensing in the following phases of landslide studies: 1. (1) Detection and classification of landslides. Special emphasis is given to the types of imagery required at different scales of analysis.2. (2) Monitoring the activity of existing landslides using G.P.S., photogrammetrical techniques and radar interferometry.3. (3) Analysis and prediction in space and time of slope failures. The different factors required in a landslide hazard study are evaluated, and the optimum remote sensing imagery for obtaining each of these factors is indicated.Examples are given of research work carried out in these three phases from EC countries. Finally an evaluation is given of the aspects of uncertainty associated with the use of remote sensing data, and conclusions are given as to the incorporation of remote sensing techniques within the overall framework of techniques.
Research into the climatic causes behind the triggering and reactivation of landslides has been carried out in two basins in the Southern French Alps, where a great many landslides have occurred over more than a century. Correlations between landslides and climate are sometimes precise and closely related in time, at other times imprecise and more distant. The better known the type of landslide and the date of its occurrence, the greater the correlation may appear. Be this as it may, climate is never the sole cause. This paper deals with the limits of the effects of climate.
The literature contains many examples, which demonstrates the importance of climatic conditions, particularly of rainfall but also temperature, on landslide activation. Normally landslides occur during specific hydrologic conditions; the relative importance of each factor will however vary with the landslide type. Heavy rains are one of the main natural factors producing landslides as they may cause pore pressure to increase on slopes or can create adverse seepage conditions, modify the slope's geometry as a result of erosion and originate swelling and softening processes in clay soils. According to their different behaviour, it is necessary to distinguish shallow or deep-seated landslides, first-time or reactivated landslides, the nature of landslide body (terrain or rock) as well as the hydrogeological nature of soils. Shallow landslides in soils and weathered rocks are often generated on steep slopes during the most intense part of a storm (lasting from minutes to several hours). The higher permeability of the outermost portion of the slope, compared to the bedrock below, allows for the creation of a temporary perched water-table, inducing the progressive increase of pore-water pressure. On the other hand, deep-seated landslides can be mobilised as a consequence of moderate intensity rainfalls lasting several days, owing to the longer recharging time required for ground-water level to rise and cause a significant build up in pore-water pressure. Pioneer studies, concerning landslides triggered by rainfalls, go back to '30s. Were selected 138 papers and key information was collected in a database. Nearly 82 % of all records are local investigations carried out in 23 countries. Italy provides the largest sample as for author’s nationality and widespread proneness to landslides; followed by United States (15 %), Hong Kong (8 %), Japan and United Kingdom. Two main approaches have been used to investigate rainfall-induced landslides: -empirical or semi-empirical relationships, using statistical correlation and forecasting techniques; -deterministic modelling of groundwater recharge and pore-water pressure changes. Studies concerning the first type of approach have reached interesting results about combination of antecedent rainfall and rainstorms intensity able to trigger widespread soilslip activation in specific geological, morphological and climatic settings. Relationships between rainfall intensities and duration associated with shallow landslides and debris flows activation has also been found and they are often used for warning purposes. For the activation of widespread mass movements, some authors underline the role of an effective rainfall period ended by a pronounced increased of rainfall intensity; in this situations hazard precursors may be considered as a combination of cumulate rainfall and rainfall intensity. The second approach requires the development of a clear picture of the modes of water flow on and below the ground surface: where groundwater flow is concerned, attention is focused on both the saturated and the unsaturated zones and complete hydrological models of slopes must be defined. The present paper is a critical overview of recent international research activity on this subject. Methods and experiences are compared and classified. Some author's direct experiences are utilised for these purposes. Published Roma
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