Landslides are one of the most devastating and recurring natural disasters and have affected several mountainous regions across the globe. The Indian Himalayan region is no exception to landslide incidences affecting key economic sectors such as transportation and agriculture and often leading to loss of lives. As reflected in the global landslide dataset, most of the landslides in this region are rainfall triggered. The region is prone to 15% of the global rainfall-induced landslides, and thereby a review of the studies in the region is inevitable. The high exposure to landslide risk has made the Indian Himalayas receive growing attention by the landslides community. A review of landslides studies conducted in this region is therefore important to provide a general picture of the state-of-the-art, a reference point for researchers and practitioners working in this region for the first time, and a summary of the improvements most urgently needed to better address landslide hazard research and management. This article focuses on various studies ranging from forecasting and monitoring to hazard and susceptibility analysis. The various factors used to analyze landslide are also studied for various landslide zones in the region. The analysis reveals that there are several avenues where significant research work is needed such as the inclusion of climate change factors or the acquisition of basic data of highest quality to be used as input data for computational models. In addition, the review reveals that, despite the entire region being highly landslide prone, most of the studies have focused on few regions and large areas have been neglected. The aim of the review is to provide a reference for stakeholders and researchers who are currently or looking to work in the Indian Himalayas, to highlight the shortcomings and the points of strength of the research being conducted, and to provide a contribution in addressing the future developments most urgently needed to obtain a consistent advance in landslide risk reduction of the area.

https://opus.lib.uts.edu.au/bitstream/10453/147477/2/applsci-10-02466-v2.pdf

Rainfall Induced Landslide Studies in Indian Himalayan Region: A Critical Review

Landslide dams are extremely dangerous because dammed rivers can inundate upstream areas with rising water levels and flood downstream areas after dam breaching. The longevity of landslide dams, which is uncertain, is of great significance for dam failure prevention and mitigation since it determines the time available to take mitigation measures. In this study, the full longevity of landslide dams is divided into three stages (infilling, overflowing and breaching) for better estimation. The influences of dam characteristic parameters (triggers, dam materials and geometric/hydrological parameters) on the full longevity of landslide dams (the period from landslide dam formation to the end of dam failure) as well as on each of the three stages are analysed based on the database. Based on eight dimensionless variables, regression models for estimating the full longevity of landslide dams are developed with a R2 value of 0.781, and regression models for the three-stage longevity (the longevity as the sum of the periods of the three stages) by considering infilling, overflowing and breaching are established with a R2 value of 0.938. It is found that the landslide dam longevity cannot be predicted by one or two influencing factors since it is affected by multiple factors. The relative importance of each control variable is evaluated based on sensitivity analysis: the trigger is the most significant variable in the breaching stage since it affects the size of dam particles, the water content and the inflow rate (e.g. the rainfall trigger results in a larger inflow rate); the lake volume coefficient is more significant in the overflowing stage because it indicates the potential volume of water eroding the dam; and the average annual discharge coefficient is the most important factor in the infilling stage because it controls the time to impound water. The longevity predicted by different models are compared. The models developed in this paper show better accuracy due to the consideration of more parameters based on more cases. In particular, the three-stage longevity regression model shows better accuracy than that of other models because it considers the particular influencing factors for each stage. Three case studies (the “10·10” Baige, Hsiaolin and Tangjiashan landslide dams) are presented to show the application of the regression models developed in this paper. The dam longevity can be predicted more precisely if the timely inflow rate can be estimated by site monitoring or multi-temporal remote sensing images and pre-event digital elevation model (DEM).

Longevity analysis of landslide dams

District census hand books

Environmental Geology, Indian Context

This work aims to understand the process of potential landslide damming using slope failure mechanism, dam dimension and dam stability evaluation. The Urni landslide, situated on the right bank of the Satluj River, Himachal Pradesh (India) is taken as the case study. The Urni landslide has evolved into a complex landslide in the last two decade (2000–2016) and has dammed the Satluj River partially since year 2013, damaging ∼200 m stretch of the National Highway (NH-05). The crown of the landslide exists at an altitude of ∼2180–2190 m above msl, close to the Urni village that has a human population of about 500. The high resolution imagery shows ∼50 m long landslide scarp and ∼100 m long transverse cracks in the detached mass that implies potential for further slope failure movement. Further analysis shows that the landslide has attained an areal increase of 103,900 ± 1142 m2 during year 2004–2016. About 86% of this areal increase occurred since year 2013. Abrupt increase in the annual mean rainfall is also observed since the year 2013. The extreme rainfall in the June, 2013; 11 June (∼100 mm) and 16 June (∼115 mm), are considered to be responsible for the slope failure in the Urni landslide that has partially dammed the river. The finite element modelling (FEM) based slope stability analysis revealed the shear strain in the order of 0.0–0.16 with 0.0–0.6 m total displacement in the detachment zone. Further, kinematic analysis indicated planar and wedge failure condition in the jointed rockmass. The debris flow runout simulation of the detached mass in the landslide showed a velocity of ∼25 m/s with a flow height of ∼15 m while it (debris flow) reaches the valley floor. Finally, it is also estimated that further slope failure may detach as much as 0.80 ± 0.32 million m3 mass that will completely dam the river to a height of 76 ± 30 m above the river bed.

Evaluation of potential landslide damming: Case study of Urni landslide, Kinnaur, Satluj valley, India

The Pawari landslide zone, located in the Satluj valley, Himachal Pradesh (India), is a progressive complex landslide zone that is ~ 900 m long and ~ 4000 m wide and encompasses an area of ~ 6 km2. It is observed that the frequency of the slope failure in the landslide zone and dimension of the landslide area have increased considerably in the last decade that pose threat to the human population of about 6000 residing in the vicinity of the landslide zone. The finite element method (FEM) and kinematic analysis are used for stability analyses, while high-resolution imagery, slope failure data and rain-gauge-based rainfall data are used to infer landslide activity. The FEM analysis involved numerical simulation of two slope models, i.e. S-1 (rockmass only) and S-2 (rockmass overlain by debris) that were chosen along the width of the landslide zone. The shear strength reduction method was incorporated in FEM to quantify the existing slope strength and to infer pattern of strain and displacement. The analyses results show that the main scarp of the landslide zone has increased ~ 7% between 2005 and 2014, and presently, major as well as minor scarps accommodate maximum shear strain (0.001–0.006) and displacement (0.08–0.20 m). The kinematic analysis reveals wedge failure in the rockmass that corroborates with the field evidences of rock failure. The present work intends to evaluate the hazard of landslide zone by analysing landslide activity pattern and determining shear strain and displacement of the slope.

Hazard evaluation of progressive Pawari landslide zone, Satluj valley, Himachal Pradesh, India

Kharsali village, located in the Northwest Himalaya near the confluence of the Yamuna River and Unta Gad, is situated on a thick (>150 m) paleolandslide deposit. The village is continuously being eroded at its base by the two rivers. Cracks are noted in most houses while the ancient Shani Temple lying to the south of the village has tilted ~5° towards the northeast. Three slope sections (S-1, S-2, S-3) were modelled and analysed to determine the displacement and shear strain patterns of the slopes. Based on surface failure conditions, potential slope instability of the Kharsali village was evaluated from 2D Finite Element Method (FEM) using Shear Strain Reduction (SSR) analysis in the Phase2 software. Results indicate a critical Stress Reduction Factor (SRF) of 1.5 for the southern edge of the village (S-1) housing the Shani Temple. The development of failure surfaces at its lower portion signifies the propagating, progressive nature of the slope. The S-2 slope section is most vulnerable to slope failure, with a critical SRF of 1.08. This has been inferred by the formation of failure surfaces with displacements of 0.05–0.08 m. The S-3 section in the northern part of the Kharsali shows highest critical SRF of 2.76. The un-metalled road section in the north of the village near S-3 has developed a failure surface with displacement of 0.003–0.004 m, and a zone of subsidence. The S-3 section is relatively stable, whereas the S-2 section is the most vulnerable portion of the village.

Evaluation of potential surface instability using finite element method in Kharsali Village, Yamuna Valley, Northwest Himalaya

Garhwal Himalaya has witnessed extreme climatic conditions in the form of incessant rainfall during June 15–17, 2013, generating numerous primary as well as secondary landslide hazards due to flooding event in the Bhagirathi River. This was probably the second highest flood after the 1978 flood in the area. The paper documents the spatial distribution of landslides and its consequences in the lower reaches of the Bhagirathi Valley between Bhatwari and Uttarkashi. It has been observed that within a stretch of 28 km in the study area, the river gradient is highly variable ranging from 3.6 to 66.6 m/km and is marked by three major knick points. These knick points are well correlated with the disposition of thrusts and a fault present in the area. An inventory of 23 active landslides has been prepared. Based on these knick points, the entire area has been divided into four zones. The area between Bhatwari and Ganeshpur is marked by the zone of transportation and between Ganeshpur and Uttarkashi, the zone of deposition of river sediments. It has been estimated that there is an average aggradation of about 0.5 m/year in the Bhagirathi River around Uttarkashi. Further, the huge volume of material deposited in the river around Uttarkashi township is posing serious threat to the slope stability on either banks of river. This calls for an urgent need for the formulation of policy for dredging the material from riverbed in order to maintain the continuous and uninterrupted flow of water during high discharge, in order to mitigate the problems of slope stability along the course of the river.

Landslide hazards around Uttarkashi township, Garhwal Himalaya, after the tragic flash flood in June 2013

An attempt is made to explain the relationship of landslides to litho-tectonic and precipitation regimes. The possible influence of these factors on the dimensional pattern of landslides is also in...

Imlirenla Jamir

Papers

Evaluation of potential landslide damming: Case study of Urni landslide, Kinnaur, Satluj valley, India

Hazard evaluation of progressive Pawari landslide zone, Satluj valley, Himachal Pradesh, India

Evaluation of potential surface instability using finite element method in Kharsali Village, Yamuna Valley, Northwest Himalaya

Landslide hazards around Uttarkashi township, Garhwal Himalaya, after the tragic flash flood in June 2013

Litho-tectonic and precipitation implications on landslides, Yamuna valley, NW Himalaya