SCIENCE REPORTER, AUGUST 2013 20

SHANTANU SARKAR

THERE has recently been a spurt in natural disasters and associated losses

around the globe, in spite of the signifi cant advancement in hazard prediction and scientifi c solutions. Though the impact of fl oods and earthquakes is more severe than landslides, frequent occurrence of landslides in hilly regions causes immense loss to lives and property. In fact, in the hilly regions of India, the cumulative loss of life and property caused by landslides is higher than other natural disasters.

Some landslide disasters in the Uttarakhand Himalayas in the recent past have been particularly devastating. Landslides in river valleys have also been accompanied by fl ash fl oods from breaching of temporary landslide dams. One of the most severe instances of this phenomenon is the recent fl ash fl ood along with debris fl ow at Kedarnath on 16 June 2013, which has claimed more than a thousand casualties.

The exact cause of the disaster is not yet ascertained. Researchers hypothesize that this disaster has been caused by excess rain in the catchment associated with landslide events in a

higher valley, which became channelised as debris fl ow. Another hypothesized cause is the breaking of a part of glacial lake situated upstream of Kedarnath.

Can a landslide hazard be prevented or minimised? All landslide hazards may not be completely prevented but the consequences can be minimised if such events can be predicted and effi cient disaster mitigation, management and preparedness are adopted. This is particularly important for developing countries, which experience higher natural disaster casualties due to higher population densities and lack of disaster preparedness.

CO

VER

CO

VER

STO

RY LandslideLandslide Risks Risks

Landslides are a common and continuous process in the hilly regions of the world. The Indian Himalayan belt is highly prone to all kinds of natural hazards, including landslides, earthquakes, avalanches, fl ash fl oods, and glacial lake outbursts. Can effi cient disaster management reduce the losses due to such disasters?

SCIENCE REPORTER, AUGUST 201321

What Causes Landslides? Landslide occurrence round the globe through the years and the observed climate change pattern suggest that increasing rainfall intensities and frequencies, coupled with population growth in hills, has signifi cantly increased landslide associated fatalities.

Landslides comprise a wide variety of complex processes that result in downward and outward movements, under gravity, of materials on unstable slopes. Some forms of mass movements like fl ows, falls, spread, subsidence and creep are also considered as part of landslide events.

Landslide can be triggered by both natural and human induced changes in hilly regions. Slope instability of a region are governed by geology, geomorphology, thrusts and faults, slope characteristics, topographic relief, drainage characteristics and land use. These are called preparatory or passive factors whose adverse nature make the slopes susceptible for landslides or in other words bring the slopes in a marginally stable condition. However, the main triggering factors that actually initiate landslides are rainfall, earthquakes, and anthropogenic activities.

Landslides also form part of a multiple hazard effect with other natural disasters, where many disasters occur simultaneously or trigger each other. Landslides can be caused by earthquakes, fl oods, and volcanic activity. Landslides can generate a tsunami if a huge amount of suffi cient landslide material slides into a body of water to displace a large volume of water. Thus, multiple hazard susceptibilities should be considered in assessing risk or creating early warning systems for landslides.

The Himalayas, one of the youngest mountains, present a dynamic geo-environment with varied rock types, seismically active tectonic zones, rugged topography, steep slopes and intense monsoon rainfall. The weak and fragile rocks along with thick overburden deposits on steep slopes are further subjected to severe weathering and toe erosion by a number of streams. In recent years, slope instability problems have been aggravated due to increased urbanization and haphazard road and hydropower construction activities.

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Uttarkashi landslide

disaster at Varunavat

Parvat (a) Pre disaster scenario

and (b) Post disaster scenario

(Source: Sarkar, S., Kanungo, D.P and Chauhan, P.K.S., 2011. Varunavat landslide

disaster in Uttarkashi, Garhwal Himalaya, India (Quarterly

Journal of Engineering Geology and Hydrology. Vol.

44; pp. 17-22)

(a)

(b)The local community should be aware and prepared for the potential risks present in the area where they live. Local groups should also be identifi ed and trained to discern early warning signs and form another channel of the early warning system by informing the appropriate District Magistrate offi ce.

SCIENCE REPORTER, AUGUST 2013 22(Source: Adhikari, Y. and Yoshitani, J., 2009. Global trend in water related disasters. The United Nations World Water Development Report 3, International Centre for Water Hazard and Risk Assessment, UNESCO, p.24.)

(a) (b)

Debris fl ow at (a) Phata and (b) Jakhla in Pithoragarh district [Source: Sarkar, S, and Kanungo, D.P., 2010. Landslide disaster on Berinag-Munsiyari Road, Pithoragarh District, Uttarakhand - an evaluation, Current Science, 98 (7), pp. 900-902]

Although in India there are many research and academic institutions engaged in different aspects of landslide research, the research outcomes have not been adequately implemented in the fi eld. There is a need to transform research outcomes into engineering practices. Further, it is pertinent to strengthen the landslide database and hazard zonation maps for pragmatic landslide risk estimation.

Landslide Hazard and Risk AssessmentLandslide risk is a measure of the magnitude of probable hazards and expected damage, i.e., the vulnerability of exposed risk elements in the form of population, infrastructures, economic

and social activities. Therefore, risk is negligible where there are no risk elements or they are not vulnerable even if potential hazard is high. On the contrary, for a large number of exposed risk elements with high vulnerability, the risk is high even if potential hazard is low.

Assessment of landslide hazard and risk is an imperative task in the area of disaster management. A simple way to estimate the hazard is by creating a database of existing landslides. The most scientifi c way to assess the hazard is by landslide susceptibility mapping. Such an effort can produce landslide hazard zonation maps, which will classify the area into various hazard classes of landslide potential zones. Such

maps of different regions of India have been prepared by various research and academic institutions.

There are different techniques available, primarily depending on the nature of data and mapping scale. Some techniques most widely being used are qualitative map combination, information model, bi–variate and multivariate statistical methods, and soft computing

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Num

ber

ofdis

aste

rs

Fata

lity

ineach

continent

Glo

balto

talfa

talit

y(T

housands)

Asia

Asia

0 0

1010

20

100

30

1,000

40

10,000

50

1980

-198

2

1980

-198

2

1983

-198

5

1983

-198

5

1986

-198

8

1986

-198

8

1989

-199

1

1989

-199

1

1992

-199

4

1992

-199

4

1995

-199

7

1995

-199

7

1998

-200

0

1998

-200

0

2001

-200

3

2001

-200

3

2004

-200

6

2004

-200

6

Africa

Africa

Americas

Americas

Europe EuropeOcearia Ocearia Total

Trends in landslide disasters and fatalities by region from 1980 to 2006

Often, the lack of sturdy foundations or the inherent instability of the landslide-prone slope is not given due attention by builders.

SCIENCE REPORTER, AUGUST 201323

A panoramic view of Kedarnath (a) before and (b) after the disaster (Source: Internet)

techniques. These maps are useful for safe land-use planning of hilly regions.

However, the maps available in our country are of small scale (1:50,000-1:25,000) and therefore detailed information about the hazards are mostly missing. Remote sensing integrated with Geographic Information System (GIS) is now extensively used for such studies. High resolution remote sensing images also help in providing detailed information about the terrain to produce large-scale hazard maps.

Landslide hazard assessment in a highly susceptible region can alsobe achieved by delineating the active/

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A framework for landslide risk assessment and management

(Source: Dai, F.C.., Lee, C.F. and Ngai, Y.Y. 2002. Landslide risk assessment and management, Engineering Geology 64, 65-87).

potential landslides through fi eld investigations and remote sensing images. Landslide hazard can also be estimated by defi ning landslide intensity, which primarily depends on landslide type, frequency, volume and expected velocity. Once the hazard is assessed, risk estimation can be carried out by estimating the probable nature and amount of losses as a consequence of a major future event. This in turn requires detailed information of risk elements such as population, properties, infrastructure, and functional activities associated within the landslide hazard area, including its run-out limit.

Landslide Monitoring and Early Warning SystemsThere is signifi cant advancement in instrumentation and sensor technologies for monitoring of natural disasters over the last few years. Valuable data from such technologies help to understand landslide mechanisms, which may help in landslide prediction. This has led to the development of the landslide early warning system.

As landslides are a continuous process, conventional monitoring of landslides may not be suffi cient to detect the initiation of a landslide at the moment it occurs. Real time monitoring, on the other hand, permits sensitive and dynamic understanding of landslides and the data can be transferred from a remote location to a control station where an accurate analysis can be carried out to envisage the landslide scenario. A real time landslide monitoring system is also an effective way to get a lead time to facilitate preparedness to face the hazard.

The exact cause of the disaster is not yet ascertained. Researchers hypothesize that this disaster has been caused by excess rain in the catchment associated with landslide events in a higher valley, which became channelised as debris fl ow. Another hypothesized cause is the breaking of a part of glacial lake situated upstream of Kedarnath.

(a) (b)

SCIENCE REPORTER, AUGUST 2013 24

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Very LowLowModerateHighVery High

Susceptibility class

Kilometers

A typical landslide susceptibility map

(Sou

rce:

Sar

kar e

t al, 2

008)

THINGS THAT COMMUNITIES LIVING IN LANDSLIDE-PRONE AREAS NEED TO KNOW

1. What are the major disaster threat percep� ons in the locali� es of immediate concern to them, and what are the projected likely disaster scenarios (landslide included)?

2. What are the possible landslide hazard distribu� on scenarios and major known landslide spots and iden� fi ed elements at risk in the area?

3. What are the lessons to be learned from past landslide disasters in the area and from their (mis)management?

4. What are the precursors and early indicators that can avert a landslide disaster?

5. What are the elements like roads, housing, schools, etc. exposed to landslide risk?

6. What is the role and responsibility of the government and local bodies before, during and a) er a disaster?

7. What are the expected roles and responsibili� es of communi� es and people at large – before, during and a) er a disaster? How much responsibility are the residents and communi� es willing to assume in choosing to live or do business in high risk areas?

8. What are the roles of the public sector, corporate sector, NGOs and other voluntary organisa� ons?

9. Does the building material, design and construc� on conform to prevalent building codes and established engineering prac� ces?

(Source: NDMA, 2009. National Disaster Management Guidelines—Management of Landslides and Snow Avalanches, National Disaster Management Authority, New Delhi, Govt. of India.)

Data collection and analysis to predict the occurrence of landslides is a challenging task. As majority of the landslides are triggered by rainfall, the most important aspect for development of an early warning system is to know the relationship between rainfall and incidence of landslides in a region. Rainfall induced landslides can be predicted by modelling the landslide events and rainfall. This is accomplished through a close network of rain gauzes and fi xing of early warning alert. The critical rainfall threshold value for landslide occurrence of a specifi c region should be known.

The type of monitoring instruments to be used depends on the landslide type and the parameters to be monitored. The most commonly used instruments for surface and sub-surface monitoring are bore hole and wire extensometers, inclinometers, tilt meters, piezometers along with rain gauzes. When the displacement or deformation data obtained from these instruments exceeds a critical threshold value, a warning signal can be issued. Today, high accuracy GPS as well as Synthetic Aperture Radar (SAR) interferometry in the fi eld of remote sensing is being used for remote monitoring of ground displacement in landslide regions. It is therefore possible to use this technique as a tool for early warning as this can detect the initiation of ground displacement before a landslide activity starts in a region.

Rapid advancement of information and communication technologyis playing a vital role in conveying early warning to the public, decisionmakers and the scientifi c community. An SMS alert could be one of the fastest means of communication for early warning.

The impact of debris fl ow, which has the most disastrous effect, can be minimized by putting check dams made of various geo-materials.It is highly recommended that all required measures should be integrated and implemented in one go for a complete solution towards landslide mitigation.

Flash fl ood caused by breaching of landslide dam in river valleys is another catastrophic event which was responsible for many disasters in the Himalayan region in the past.

SCIENCE REPORTER, AUGUST 201325

Landslides, Buildings and InfrastructureBuildings on landslide prone slopes compound the disaster vulnerability as their collapse multiplies injuries to the human population. Often, the lack of sturdy foundations or the inherent instability of the landslide-prone slope is not given due attention by builders. Constructions of already questionable safety cannot be bolstered by retrofi tting of the superstructure if these factors are not accounted for at the initial building stage. Public facilities like hospitals, government buildings, schools, communication and transport networks, etc. should be protected against landslide hazards.

Landslides can destabilize or destroy foundations, walls, and underground utilities. Fast moving debris fl ows are particularly destructive due to the high velocity, volume of material and

lack of notice. Even overlooked slow-moving landslides can completely destroy structures over time. Rebuilding of the damaged area or success of the mitigation measures are often compromised as these landslides continue to move for days after the damage.

One of the greatest damage from landslides is to the transportation infrastructure. Common problems along roads and railways include cut-and-fi ll failures, rockfalls and maintenance problems. The blocking of road or rail by debris and rocks is a common experience, and hampers commercial activities, tourism, and emergency activities.

Landslide hazards can be minimized by avoiding constructions in landslide-prone regions. Suitable land-use policies can be developed based on hazard zonation maps. For instance, no infrastructure development projects should be allowed in landslide-prone regions.

Sometimes, avoiding construction on some sites is not feasible due to the high cost of opportunity and public opposition. This calls for technological solutions to control landslides.To prescribe a suitable remedial measure, a thorough understanding of the landslide processes should be developed by an in-depth scientifi c investigation.

Successful landslide stabilization depends on scientifi c investigation, construction methods and cost evaluation. There are various landslide control measure techniques available today.

Since the majority of landslides are triggered by rainfall, drainage is considered to be the primary measure. Drainage measures include surface and subsurface drainages that help to take away the water out of the active landslide area. The lowering of ground water by sub-surface drainage helps in decrease of pore water pressure, increase of shear

COVER STORY

Landslides mapped on satellite image along Pipalkoti-Joshimath

Highway of Uttarakhand Himalayas

Debris Slide

Debris Flow

Rock & Debris Slide

Debris Slide Road

Alakhnanda R

iver

Rock Slide

SCIENCE REPORTER, AUGUST 2013 26

Hasan Jawaid Khan: Would you say that the fall-out of the recent natural disaster in Uttarakhand was further compounded due to innumerable building structures coming up in the area not following proper norms?S.K. Bhattacharyya: Yes. A number of non-engineered buildings are constructed in the areas. Part of the present disaster is due to that.

HJK: The hills are sensitive zones. Has CBRI worked on estimating the average structural load that hills can bear and beyond which they become unstable?S.K. Bhattacharyya: Well, CBRI has not worked on how much structural load hills can bear in general. Actually, bearing capacity of soil or rock depends on several factors and cannot be unifi ed for all cases. However, CBRI gets involved in estimating the load carrying capacity of areas where important engineered structures are constructed.

HJK: Has the load-bearing capacity of hills been reduced over the years due to certain reasons?S.K. Bhattacharyya: In hilly areas, geological faults do exist in the rocks. In some areas along fault lines, there is a possibility of reduction of capacity. Also, lot of interventions are taking place in hills due to the construction of roads, etc. These activities can activate fault lines and thereby can affect the load carrying capacity.

A Professor in the Department of Civil Engineering, IIT Kharagpur and an Adjunct Professor in BITS, Pilani, Rajasthan, Prof. SRIMAN KUMAR BHATTACHARYYA is currently Director of the Central Building Research Institute (CBRI), Roorkee, a constituent laboratory of the Council of Scientifi c and Industrial Research (CSIR). CSIR-CBRI has been vested with the responsibility of generating, cultivating and promoting building science and technology in the service of the country.In light of the recent devastation in the Uttarakhand disaster, in an e-mail interview with Hasan Jawaid Khan, Prof. S.K. Bhattacharyya talks about the need for exercising caution while building structures in regions prone to earthquakes and landslides.

HJK: Has your institute worked on identifying certain areas in hilly regions that are unfi t for building structures or areas that are more prone to landslides and hence not safe for buildings?S.K. Bhattacharyya: Yes, CBRI along with Remote Sensing Institute of Dehradun has prepared a map indicating the landslide prone zones. It is preferable to avoid those areas for any construction of buildings without taking any measure for controlling the landslides.

HJK: Can you give us an idea of some of the most important norms and regulations that need to be followed while building structures in hilly areas, especially those are prone to landslides?S.K. Bhattacharyya: While constructing any building in any area, it is advisable to look into the prior history of the region in terms of any natural disaster. In hilly areas, it is to be looked into whether the area was affected by earthquake, fl ash fl oods or landslide before. If yes, then appropriate safeguards are to be taken to make the buildings resistant against such disasters. In landslide prone areas, buildings should be constructed only when it is possible to adopt some control measures for the landslide.

HJK: Has CBRI come out with building technologies for landslide prone areas?S.K. Bhattacharyya: So far as the building technologies are concerned, they are more or less of similar nature. However, for landslide prone areas, control measures are required to be devised for controlling landslides and thereby prevent buildings from collapse.

HJK: Has your institute also worked on building sustainable structures with locally available materials?S.K. Bhattacharyya: Yes, CBRI has worked on construction of buildings with locally available materials.

HJK: Is there any way of strengthening existing structures?S.K. Bhattacharyya: Existing engineered buildings can defi nitely be strengthened if any defi ciency is detected.

HJK: Has there been an effort at disseminating information on the best practices to be followed while building structures in hilly areas? Has your institute tried to reach out to hill communities?S.K. Bhattacharyya: Yes, We have a group that disseminates the technologies developed by CBRI to different hill states through exhibitions, short programmes in association with the State Science & Technology Departments, etc. Also, we have created CDs, charts, etc for disseminating the building construction technologies in hilly areas for common people.

HJK: For areas that have been completely washed out in the recent landslides and fl oods, what would you suggest as an ideal rebuilding plan?S.K. Bhattacharyya: It will be appropriate to study the area very carefully from the considerations of earthquake, landslide, fl ood-plane, etc. Depending on the possibilities of any of the disasters, appropriate actions are to be taken to safeguard the constructed buildings. Appropriate design measures are to be adopted to make the buildings safe against any such disasters.

It is preferable to avoid these areas for any construction of buildings without taking any measure for controlling the landslides.

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�

SCIENCE REPORTER, AUGUST 201327

Drum retaining wall and gabion wall implemented at landslide sites (Source: CSIR-CBRI, 1988. Eco Development in the Garhwal Himalaya with particular reference to fi eld study and monitoring of landslides & development of innovative control measures, Technical Report, p150.)

COVER STORY

strength, and reduction of seepage and erosion. Because of its high stabilization effi ciency in relation to cost, drainage is the most widely used and generally the most successful stabilization method.

Retaining structures like concrete masonry wall, gabion wall, crib wall, soil reinforced wall, etc. are the second line of remedial measures. These days gabion walls are the most preferred retaining structures as they are quite fl exible and allow water to pass through. These are more economical than other rigid structures because they can be constructed using locally available rocks.

Another cost-effective retaining wall is the drum-retaining wall that makes use of landslide debris and the empty bitumen drums that are available in abundance with construction agencies. The drum-retaining wall consists of empty bitumen drums arranged in two rows and fi lled with debris. The drums are interconnected both vertically and horizontally and

anchored at the base and backfi ll. The effi cacy of such walls has been proven as one such wall implemented at a landslide site stood well for more than 15 years before it was removed for widening of the highway.

Soil reinforcement by various techniques such as soil nailing, geogrid and fi bre reinforcement and application of piles are some of the measures used for soil slope stabilization. Bio-engineering measures for slope protection are now being widely used for unstable soil slopes. Biotechnical stabilization makes use of structural elements and biological elements together to arrest slope failures and erosion. These measures are less costly and more eco friendly than the other measures.

In case of rock slopes, the stabilization measures include rock bolting, rock anchoring, shotcrete, tieback wall, etc. The impact of debris fl ow, which has the most disastrous effect, can be minimized by putting check dams made of various geo-materials. The other catastrophic events resulting from rock falls can be checked by installing rock catch fences, barriers and ditches. Rock sheds over roads are sometimes used to protect vehicular traffi c from rock falls where rock slope stabilization is not a viable solution.

It is highly recommended that all required measures should be integrated and implemented in one go for a complete solution towards landslide mitigation. Flash flood caused by breaching of landslide dam in river valleys is another catastrophic

event which was responsible for many disasters in the Himalayan region in the past. It is very essential to estimate the size of the reservoir and dam and the consequences of dam failure in the downstream valleybefore suggesting any remedies. In a common practice, spillways, tunnels and sometimes extensive blasting are used to break the dam in a phased way to release the reservoir water.

Role of Awareness and TrainingAwareness and educational training is an integral part of any disaster management programme. There is a need for providing necessary training to engineers and administrators engaged in disaster management. The local community should be aware and prepared for the potential risks present in the area where they live. Local groups can also be identifi ed and trained to discern early warning signs and form another channel of the early warning system by informing the appropriate District Magistrate offi ce.

As the hills are exploited by extensive construction activities, the adverse effects of anthropogenic factors should be stipulated very clearly to the engineers, architects and builders. It is also important to disseminate the knowledge and research outcomes of the scientifi c community to the Central and State agencies dealing with landslide disaster management.

Dr Shantanu Sarkar is a Senior Principal Scientist at CSIR-Central Building Research Institute, Roorkee. Email: shantanu_cbri@yahoo.co.in

Constructions of already questionable safety cannot be bolstered. Public facilities like hospitals, government buildings, schools, communication and transport networks, etc. should be protected against landslide hazards.