Moderate Hazard Zones Research Articles

The Landslide Threat Evaluation and Zoning in The Birbir Mariam District, Gamo Highlands, Ethiopia Great Rift Valley Escarpment Using Slope Susceptibility Analysis and Geospatial Techniques

The current research focuses on landslide assessment and hazard zonation in the Birbir Mariam district of the Gamo Highlands. The study examined landslide causative factors and used the slope susceptibility evaluation parameter to create a landslide hazard zonation covering an area of 110 square kilometers. The landslide hazard zonation was classified using facet-wise observation. As a result, the intrinsic and external causal parameters of score schemes have been held responsible for slope instability. Inherent causative elements consist of slope geometry, slope material (rock or soil), structural discontinuities, land use or land cover, and groundwater conditions. Rainfall and human interest have seemed like external elements. The intrinsic and external triggering elements for every facet (a total of 106) were rated for their contribution to slope instability. Finally, an evaluated landslide hazard value was calculated and classified into three landslide hazard classes. According to the findings, the area has a high hazard zone of 18.87 percent (20.76 km2), a moderate hazard zone of 54.72 percent (60.19 km2), and a low hazard zone of 26.41 percent (29.05 km2). The methodology employed in this investigation, as well as the resulting landslip susceptibility zonation map, were both reliable and applicable to other places with similar geology and topographic circumstances. 
 Keywords: Landslide evaluation, Slope stability, Landslide, Hazard zonation, Ethiopia

Tunnel Stability Analysis Under Seismic Load Using Finite Element Method: A Case Study of Spillway Tunnel, Sidan Dam, Bali, Indonesia

The location of the Sidan Spillway Tunnel, as shown on the Earthquake Hazard Zone Map of Bali Island, is in a moderate hazard zone. The support system of the spillway tunnel of the Sidan Dam, Indonesia, was empirically designed based on rock mass classification systems. The objective of this research was to verify the performance of the proposed support system by a numerical method considering the uncertainty in using rock mass classification systems for designing a tunnel support system. In addition, being located in an active seismic region, the seismic load was not considered in the empirical tunnel support design. The proposed tunnel support design was numerically modeled in two dimensions using a finite element method and subjected to a seismic load obtained from probabilistic seismic hazard analysis. A numerical analysis without seismic load was also conducted for comparison. Phase2 software was used for the tunnel stability analysis. The input parameters in the numerical analysis were derived from field investigations (surface engineering geological mapping and evaluation of drilling cores) and laboratory tests. The spillway tunnel area consists of pyroclastic rocks, and the Generalized Hoek-Brown Failure Criterion was selected for the strength parameter of rocks. The suggested support designs are systematic rock bolts (20 mm diameter fully grouted), wired mesh, shotcrete, and steel ribs at specific locations. The numerical models determined that applying the proposed tunnel support system recommended based on the empirical method resulted in a roof strength factor of more than 1.5 under static load & 1.1 under seismic load and roof displacements lower than a 10 cm maximum displacement at every stage of construction. The results verify that the tunnel construction will be stable and fulfill the required safety standard, both under and without seismic loads.

Determining the effect of urbanization on flood hazard zones in Kahramanmaras, Turkey, using flood hazard index and multi-criteria decision analysis.

Floods are the most destructive natural hazard throughout the world. Identifying flood hazard zones is the first step in flood risk management. Land use changes, especially urbanization, is the key factor in the destructiveness of flood events and change in flood risk. Therefore, determining the effect of urbanization on the changes in flood hazard zones presents a valuable data for effective flood risk management and urban development planning. In this context, the aim of this study is to reveal the effect of urbanization on flood hazard zones in Kahramanmaras city. In this study, an index-based approach was used to identify the flood hazard zones. To calculate a flood hazard index, the susceptibility map was multiplied by the land use map by using the raster calculator tool in the ArcGIS. The susceptibility map was generated by combining the maps of flow accumulation, distance to stream, slope, and elevation parameters based on parameter weights obtained from the analytical hierarchy process (AHP) method. Two land use maps for the years 1990 and 2018 were separately overlaid with the susceptibility map to reveal the effects of urbanization on flood hazard zones. According to the results, it was found that very low, low, and moderate hazard zones decreased by 0.01%, 0.09%, and 1.2%, respectively whereas the high and very high zones increased by 3.30% and 0.58%, respectively due to urbanization. It was also determined that the main reason for the increase in the high zone was the expansion of urban areas into agricultural areas in the study area.

Preliminary Study of Landslide Hazard in Kutai Kartanegara Regency, East Kalimantan using Digital Elevation Model

The Kalimantan Island is part of the Sundaland crust, namely the Eurasian Continental Plate. The plate is moving to the southeast colliding with the Indo-Australian plate which is moving north. Whereas for Kutai Kartanegara Regency in the Kalimantan Island position is far from the collision zone, so it is relatively stable tectonically. This is important to research that is, due to tectonic processes that occurred earlier, resulting in the formation of geological structures, especially faults. The purpose of the study was to determine the morphotectonic and landslide hazards in the Kutai Kartanegara Regency, where this research was carried out quantitatively with data collection techniques, then analyse landslide hazards based on data; DEM (Digital Elevation Model) including the slope, slope direction, and slope length for vulnerability analysis, geological data from Regional Geological Maps, which include rock formations, distances from faults data and administrative boundary spatial data in the form of vector GIS for the preparation of landslide hazard maps. The result showing Kutai Kartanegara predominantly categorized as moderate to high hazard zone. The low hazard zone covering 9.88% area, moderate hazard zone covering 35.81% area, and 54.31% area is high hazard zone of landslide. The analysis showing that the hazard of the research area consist predominantly sedimentary rocks and controlled by structural geology identified as thrust fault, strike slip fault, and fold which include in Anticlinorium Samarinda. Those lithology and geological structure features along with the slope are identified as controlling factor to the landslide hazard in the research area.

Zonation of Landslide Hazards Based on Frequency Ratio Modeling at Coonoor and Kothagiri Taluks of Nilgiri District, Tamil Nadu, India

A frequency ratio model is developed within the framework of a Geographic Information System (GIS) to map landslide hazards in a mountainous environment. The Nilgiri Hills (Mountains) of Tamil Nadu are prone to landslides; these landslides are typically the result of the structural failure of thick laterite soils that have been saturated by heavy rains during the monsoon season. The GIS based analysis in the present work incorporates the frequency ratio values from the existing landslides. The landslide inventory of paleoscars was located by a collection of existing historical reports. Detailed field surveys have been carried out in the study area. In the observation, 118 landslide locations were identified and mapped by GIS; out of that, 83 (70 %) locations were randomly selected for the training data set and the remaining 35 (30 %) cases were used for the model validation purposes. For spatial modeling, the landslide triggering parameters include active-passive slope, concave-plain-convex slope, drainage density, dissected-undissected slope, geology, geomorphology, lineament density, lineament frequency, lineament intersection density, land use / land cover, rainfall, regolith cover, shallow-moderate-steep slope, soil and water level for landslide hazard zonation. This model has been used to spatially classify the study area into three zones viz; high, moderate and low landslide hazard zones. The frequency ratio model was validated with the existing landslide location data using R-index method. The validation of the results showed that the values is 1115.23 in R-index as high hazard zone when R-index increases with the level of susceptibility. The obtained results will provide a basis for planning, risk reduction strategies and various developmental activities in the Nilgiri area.

Landslide hazard zonation and evaluation around Debre Markos town, NW Ethiopia—a GIS-based bivariate statistical approach

The main purpose of this study was to perform landslide hazard zonation and evaluation around Debre Markos town, Northwest Ethiopia. This was achieved using a GIS-based bivariate statistical technique. Initially, a landslide inventory map containing information on past and active landslide locations was prepared. In this study, eight conditioning factors, including slope material (lithology and soil mass), elevation, aspect, slope, land use, land cover, curvature, distance to fault, and distance to drainage, were identified and integrated with the ArcGIS platform. Data were collected from field mapping, satellite images, and digital elevation models. All conditioning factors were statistically analyzed to determine their relationship to previous landslides. The hazard map revealed that 17.15% (40.60 km2) of the study area falls under no hazard zone, 25.53% (60.45 km2) in low hazard zone, 28.04% (66.39 km2) in moderate hazard zone, 18.93% (44.83 km2) in high hazard zone, and the remaining 10.36% (24.54 km2) in very high hazard zone. The validation of the landslide hazard zonation map shows that 94% of past landslides fall in high or very high hazard zones, while 3% fall in moderate hazard zone, 2% fall in low hazard zone, and 1% fall in no hazard zone. The validation of the LHZ map thus, reasonably showed that the adopted methodology produced satisfactory results. The delineated hazard zones may practically be applied for the regional planning and development of infrastructures in the area. The results also indicated that slope angle, distance to fault, distance to drainage, and slope material types were statistically significant in controlling the landslides.

Landslide Hazard Assessment and Zonation by using Slope Susceptibility Evaluation Parameter (SSEP) Rating Scheme- a Case from Debre Sina, Northern Ethiopia

Rainfall-induced landslides of different types and sizes frequently affect the hilly and mountainous terrains of the highlands of Ethiopia. The principal objective of the proposed research study was intended to prepare a landslide hazard zonation map of the area, particularly for hazardous zones. In the present study, the Slope Susceptibility Evaluation Parameter rating scheme has been implemented as a relevant approach to map the landslide hazard of the Debresina area, which has experienced slope failure problems for a long period of time. The geology of the area includes quaternary sediments, ignimbrite, rhyolite, different kinds of basalts, and tuff deposits, which are highly weathered and changed into unconsolidated sediments at some localities. Locally observed geological structures such as joints, dykes, and other discontinuities have a considerable role in the initiation of landslide hazards. As a general methodology, a facet map was prepared from a topographic map (1:50,000) and rating values were assigned to each causative parameter (both intrinsic and external) based on its severity in triggering landslide hazard. The study area was classified into three hazard classes, of which 25 % of the slopes fall into a moderate hazard zone, while 58 % and 17 %were found to be high and very high hazard zones, respectively. Validation of the landslide hazard zonation map with past landslide activities suggests the rationality of the considered governing parameters, the adopted technique, tools, and procedures in developing the study area's landslide hazard map. Further, in order to validate the landslide hazard map prepared during the present study, active landslide activities and potential instability areas, delineated through inventory mapping, were overlaid on it, which yielded promising results.

Reducing sea cliffs hazards in pocket beaches through beach nourishment on the Barlavento Coast (Algarve, Portugal)

Tourism based on “sun and beach” is the main economic activity in the Algarve region. A considerable part of the beaches of the Barlavento coast corresponds to embedded sand accumulated along the irregular lacework-like coastline of rocky cliffs cut into Miocene calcarenites. The pattern of touristic occupation in the Algarve and the geodynamics of the rocky sea cliffs, characterized by discontinuous and intermittent occurrence of slope mass movements, result in a high level of risk to beach users along pocket beaches. In order to mitigate the risk associated with the cliff geodynamics, artificial beach nourishment was performed in Castelo and Coelha pocket beaches on the Barlavento Coast, in 2014, increasing the beach area by 3.5 times. The effects of the beach nourishment on the occupation patterns of those beaches along the 2006-2016 decade, before and after the beach nourishment, are herein presented and discussed. Occupancy data were obtained covering different seasons along the year, by counting the number of beach users, regardless of age, using periodic and systematic photographs taken at strategic points that provide full coverage of the beach areas. Before the beach nourishments the area of dry sand outside high and moderate hazard zones, measured at half-tide under average summer wave conditions was 500 m2 at Coelha beach and 800 m2 at Castelo beach. After beach nourishment the same area increased to 6700 m2 at Coelha beach and 7100 m2 at Castelo beach. Results show that, following the beach fill, beach occupation by recreational users naturally shifted seaward, moving out from the cliff hazard areas. After the intervention, the occupation of high and moderate hazard areas reduced significantly, from 37 % to 11 % in Castelo beach and from 59 % to 27 % in Coelha beach. Keywords: beach nourishment; hazard; rocky cliffs; Algarve; Portugal.

ASSESSMENT OF VULNERABILITY IN AGRICULTURAL LAND IN FLOOD PRONE AREAS AND APPLICATION OF MOBILE SMART PHONE IN PROVIDING FLOOD HAZARD INFORMATION IN LAM RIVER BASIN (VIETNAM)

Floods are considered to be one of the most costly natural hazards in the Lam river basin causing infrastructure damages as well as devastating the affected area and relatively high death toll. So prevention is necessary for shielding lives and properties. The flood management on the Lam River basin has been considering for many years to minimize damages caused by flooding. The flood hazard zoning map is one of the indispensable tools to provide information about hazard and risk levels in a particular area and to perform the necessary preventive and preparedness procedures. The multicriteria decision analysis based on geographic information systems is used to build a flood hazard map of the study area. The analytic hierarchy process is applied to extract the weights of six criteria affecting the areas where are prone to flooding hazards, including rainfall, slope, relative slope length, soil, land cover, and drainage density. The results showed in 91.32 % (20103.83 km2) of the basin located in the moderate hazard zones to very high hazard zones. Accordingly, this study also determined 4 vulnerability levels to agricultural land including low, medium, high, and very high. About 94% of the total area of agricultural land in the basin are classified into moderate to the very high hazard of flood vulnerability. The paper presents a method that allows flood risk areas in the Lam River basin to receive information about flood risks on a smartphone, making them more aware.

Impact of Land use Changes on Landslides Occurrence in Urban Area: The Case of the Constantine City (NE Algeria)

The city of Constantine (NE Algeria), the third largest city of the country (2.374 inhabitants/km2) is facing frequent damaging landslides that constitute a constraint to future development and land use planning. The main goals of this study are to evaluate the effect of land use changes on the spatial distribution of landslide hazard occurrence and give an example of landslide hazard assessment as useful tool within the context of long-term land use planning in the urban area of Constantine. For this purpose, the adopted methodology requires four steps: (i) Data collection and construction of a spatial database related to the historical landslides, land use, building and population inventory; (ii) landslide inventory and land use mapping for the period of 1970 to 2011 based on the analysis of aerial photographs, high resolution satellite images, historical records verified and completed by extensive field observations, (iii) analysis of the effects of land use changes on the spatial distribution of landslide occurrence for different periods 1970 and 2011; (iv) landslide hazard map, obtained by using the frequency ration (FR) under GIS and (v) evaluate the impact of human-induced land use changes on hazard occurrence. For that, we, firstly, compared the landslide inventory map with land use maps of different periods of 1970 and 2011 that showed that since 1970, the density of landslides increases with increasing of urban areas. In 2011, the high landslide density is concentrated on the following four layers: the urban area layer (41%), the agriculture land layer (39%), the grass area layer (15%) and the forest land layer (5%). The effect of the expansion of urban zone in agriculture, grass and pasture area have increase landslide densities over time. Secondly, we compared the landslide hazard map to these land use maps and we found that 40% of the high hazard zones and 50% of the moderate hazard zones fall in the urbanized area. The obtained results show a clear impact of the changed land use where human action is an important triggering and/or accelerating factor of landslides in the urban area of Constantine. Nowadays, about 72,749 inhabitants and 25,255 buildings are located in landslides threatened area. Therefore, landslide hazard maps should, always, guide the land use and urbanization in landslides prone areas.

Flood Hazard Mapping and Assessment on the Angkor World Heritage Site, Cambodia

World Heritage sites in general are exposed to the impacts of natural hazards, which threaten their integrity and may compromise their value. Floods are a severe threat to the Angkor World Heritage site. Studies of regional floods and flood hazard zoning have played an increasingly important role in ensuring sustainability of the Angkor site. This study developed a flood hazard index (FHI) model based on a geographic information system (GIS) and used synthetic aperture radar (SAR) data to extract historical floods at Angkor from 2007 to 2013. Four indices (flood affected frequency, absolute elevation, elevation standard deviation, drainage density) were used to identify flood-prone areas. The Analytic Hierarchy Process (AHP) and the Delphi method were employed to determine the weight of each index. The weighted indices were then used to develop a distribution map of flood hazards at Angkor. The results show that 9 monuments are at risk by potential floods among the 52 components of the Angkor monuments. The high hazard and moderate-to-high hazard areas in the core zone are mainly located surrounding the West Baray but will not bring direct risk impact on the monuments located in the core archaeological zone. The moderate hazard areas are located on both sides of the Siem Reap and Roluos rivers and in the flooded area of the Tonle Sap Lake in the core archaeological zone. These areas cover 19.4 km2, accounting for 9.13% of the total area of the core zone. This moderate hazard zone poses a greater flood threat to the core zone and must be given higher attention. The buffer zone is a small area with fewer sites. As such, flooding has a low impact on the buffer zone. The methods used in this study can be applied to flood hazard assessments of other heritage sites in Southeast Asia.

Determination of Veld Fire Hazard Zones in Multiple Tenure Systems in Zimbabwe: Implications for Intervention

The study determined fire hazard zones in multiple tenure systems from 2001 to 2013 in Mazowe district, Zimbabwe, using Landsat 7 and 8 30m resolution images, a fire hazard model and weighted sum of burnt area. The model divided the district into high, moderate and low fire hazard zones across five tenure systems that obtain. Most of the district (50%) was in the high hazard zone. Fire events superimposed onto the zones confirmed that most of the fire events (60%) occurred in the high hazard zone. The weighted sum of burnt area revealed that 47% of the study area was not burnt. The level of fire risk in terms of pasture per livestock unit was substantially high. At 1% of land burnt four times in A2 and Communal systems involved losses of 2784 and 1682 livestock units' worth of pasture respectively. The hazard zones show hotspots needing monitoring, fire problem occurring irrespective of tenure and that the problem could be addressed. The study recommends setting up a fire command centre, involving all parties, urgent attention to the fire problem across tenure and adoption practices such as law enforcement, hierarchical structures and participation of grassroots communities in addressing the fire problem.

Landslide hazard zonation mapping on meso-scale in SH-37 ghat section, Nadugani, Gudalur, the Nilgiris, India

Landslide is the most common natural disaster in mountainous regions. It causes damages to life and properties. The study area, Calicut–Nilampur–Gudalurghat section (SH37) falls under the Survey of India toposheet 58A-7/NE (1:25,000). The present study was carried out with landslide hazard zonation mapping on meso-scale. This paper explains how meso-zonation of landslide hazards (facet-wise) was made from investigations as per the norms given in Bureau of Indian Standard IS 14496:1998. Remote sensing and geographic information system (GIS) was utilized for the preparation of thematic maps on 1:10,000 scale. The present study evaluates more detailed related factors of inherent causative factors (lithology, structure, slope gradient, relative relief, land use/land cover, and hydrogeology) involved in landslides. This method also incorporates effects of external causative factors like seismicity and rainfall as corrected rating. In the study area, 10 different facets have been identified. This area falling in facets 3, 4, 6, 7, and 10 come under high hazardous zone, the slopes falling in the facets 1 and 5 fall in the moderate hazardous zone, facet 2 in low hazard zone and other facets 8 and 9 show very high hazardous zone. Details of this work are presented in this paper. The landslide inventory points were collected with the help GPS in this ghat section. The inventory percentage 3.3% comes in low hazard zone, 18% present in moderate hazard zone, 57.4% in high hazard zone, and 21.3% under very high hazard zone.

Landslide hazard zonation mapping and cut slope stability analyses along Yercaud ghat road (Kuppanur\u2013Yercaud) section, Tamil Nadu, India

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.

Population Based Binary Reclassification of Indian Standard Landslide Hazard Model

ABSTRACT GIS complemented statistical classification techniques yield good result in predicting landslide hazards. Indian standard landslide hazard model follows guidelines formulated by the Bureau of Indian Standards (BIS, 1998), in which the study area is divided into five categories, ranging from very low hazard zone to very high hazard zone on fixed numerical ratings. For land use planners, “moderate hazard zone” proves vague and indecisive. In the present study, BIS based landslide hazard zones are demarcated for 140 sq. km area for a road corridor in East and North Sikkim that shows 21.96%, 53.14%, 22.80% and 2.10% for ‘Low Hazard Zone’, ‘Moderate Hazard Zone’, ‘High Hazard Zone’ and ‘Very High Hazard Zone’ respectively. This classification scheme has been reclassified to binary system based on population distribution and defining the cut-off by evaluation techniques of the ROC. The reclassification eliminates “moderate hazard zone”, minimizing the Type-II error and becomes more acceptable for future land use planning.

Potential landslide susceptibility mapping using weighted overlay model (WOM)

Present study presented a methodology for landslide susceptibility mapping using an integrated geospatial technology and ground based observation. IRS LISS-III satellite data, drainage, slope, aspect, geology, geomorphology and land use were integrated into GIS platform to delineate landslide susceptibility zone based on weighted index overlay method. The resulting landslide susceptibility map identified five zones of susceptibility of landslide hazards, viz very high hazard zone (10 %), high hazard zone (23 %), moderate hazard zone (25 %), low hazard zone (32 %), and very low hazard zone (15 %). The outcome was confirmed by relating with the landslide occurrences in different classes.

Soil gas radon mapping of Muzaffarabad city, Pakistan

Soil-based radon investigations are of value in correlating radon production and its transportation into buildings through the processes of convection and diffusion. Such studies can help in identifying land areas that pose special concerns. We present preliminary results of soil radon gas measurements at 60 different locations in an attempt to map out the geohazard zone of the city of Muzaffarabad. The seismic geohazard microzonation for the area includes five microzones based on different hazard parameters: a very high hazard zone, a high hazard zone, a moderate hazard zone, a low hazard zone, and a safe zone. Measurements were taken with an active radon monitoring system at the depths of 30, 40, 50, and 60 cm below the ground surface. The results obtained were explained by the lithology of the area. Average soil radon gas concentrations were correlated with the depth from the ground surface and indoor radon values for the study area. No significant correlation was found between soil radon gas and meteorological parameters, however soil radon gas increases as the depth from the surface of the ground grows. The results showed a linear relation between soil radon concentrations with depth from ground surface (R2 = 0.9577). The minimum soil radon concentration (68.5 Bq/m3) was found at a depth of 30 cm in the very high hazard zone, the maximum value (53.300 Bq/m3) at a depth of 60 cm in the seismically safe zone. Measured soil gas radon concentrations at depths of 30, 40, 50, and 60 cm were mapped for high, moderate, and low radon concentrations. Elevated soil radon gas concentrations were found in the safe zone, otherwise considered to be suitable for any type of construction.

Landslide hazard zonation mapping using frequency ratio and fuzzy logic approach, a case study of Lachung Valley, Sikkim

Abstract Background Sikkim Himalaya is under consistent distress due to landslides. Abrupt thrust on infrastructure development in the valley regions of Sikkim Himalaya has led to a need for a prior planning to face landslide hazard. A comprehensive study for the identification of landslide hazard zones using landslide frequency ratio and fuzzy logic in GIS environment has been presented for the Lachung valley, Sikkim, India, where a number of hydroelectric projects are proposed. Temporal remote sensing data was used to generate significant landslide causative factors in addition to landslide inventory. Primary topographic attributes namely slope, aspect and relative relief were derived from digital elevation model. Landslide frequency ratio approach was adopted to correlate landslide causal factors with landslide incidences. Further, fuzzy logic method was used for the integration of landslide causative factors in order to delineate the landslide hazard zones. Fuzzy memberships were derived from the landslide frequency ratio values. Different gamma values were used in fuzzy gamma integration process, which resulted different landslide hazard index maps. Receiver operating characteristic curves were prepared to analyze consistency of the resulting landslide hazard index maps. Results Landslide frequency ratio values have emphasised the importance of factors/classes in landsliding. High slope angle (35°-45°), very high slope category (&gt;45°), High and very high relative relief categories; south, southeast and southwest aspects; drainage and lineaments buffer range of 0-50m, 50-100m and 100 to 150m; quartzite/garnet schist and migmatite type of lithology; Sandy loam and Rock/loam classes of soils; fallow land and sparse vegetation classes of land use/land cover were found to be associated with landsliding. Five landslide hazard zonation maps with each comprising five relative landslide hazard zones namely; very low, low, moderate, high and very high hazard zones were prepared by using five fuzzy gamma operators. Maps indicated that steep talus slopes, close proximity to drainages, ridges and spars fall under high hazard zones. Settlement areas were observed in low to moderate hazard zones. Very high hazard zones were observed in steep slopes, cliffs and cut slopes excavated for the roads. Low hazard zones were observed in agricultural terraces and permafrost areas. Conclusions Hence it can be concluded that landslide causative factor’s integration using fuzzy logic has yielded good results for Lachung valley. Frequency ratio method for determination of fuzzy membership value has reduced subjectivity in the model. The final LHZ map (γ = 0.92) can be used for the planning of future infrastructure, settlement and ecological development in Lachung region.

Comparison of results of BIS and GSI guidelines on macrolevel landslide hazard zonation — A case study along highway from Bhalukpong to Bomdila, West Kameng district, Arunachal Pradesh

This paper compares the findings of macrolevel landslide hazard zonation carried out along the highway from Bhalukpong to Bomdila, West Kameng district, Arunachal Pradesh following GSI and BIS guidelines. The map resulted from the GSI guideline shows that 69.31% of the faceted area falls under the Low Hazard Zone (LHZ) while 17.69%, 7.31%, 5.03% and 0.65% of the area are in Moderate Hazard Zone (MHZ), High Hazard Zone (HHZ), Very Low Hazard Zone (VLHZ) and Very High Hazard Zone (VHHZ) respectively. Correlation between the landslide incidences and different hazard zones reveals that maximum failure percentage is in VHHZ and it is followed by HHZ, MHZ and LHZ. The second map resulting from BIS guideline reveals that 45.77% of the faceted area falls under MHZ while 41.39%, 11.52% and 1.29% of the area are in HHZ, LHZ and VHHZ respectively. Not a single facet falls in VLHZ.With regard to failure percentage VHHZ experiences 50%, while that of HHZ, MMH and LHZ is roughly 11.5% each. In the study area, the landslide hazard zonation map resulting from GSI guideline broadly conforms to field condition. It may be due to the fact that the study area is along the road corridor where slope cutting and landslides are very common and GSI guideline considers both the slope cutting and landslide parameters, while it is not so in the case of BIS guidelines. However, a final conclusion can be drawn after carrying out such studies in different geological settings.

Demarcation of potential avalanche sites using remote sensing and ground observations: a case study of Gangotri glacier

This study demonstrates the effectiveness of remote sensing and analytical hierarchy process for avalanche hazard mapping. The layers incorporated in this study were of slope, aspect, profile curvature, ground cover and elevation. The accuracy of output was determined using the registered avalanche sites based on ground observations and field-based modelling techniques. 93.35% of avalanche-affected areas came under maximum and moderate hazard zones, thus proving the effectiveness of this technique for Gangotri glacier basin. A parallel study was done to observe the change in the results, if any, by using high-resolution DEM and Cartosat-1 imagery. Similar methodology was adopted and the outcome was having significant improvement over the previous result as 98.8% of the preregistered avalanche area falling within maximum and moderate hazard zones.