:: Natural Disaster Mitigation

Natural Disaster Mitigation

The Indian subcontinent has a highly diversified range of natural features. The Himalayas, which are the young fold mountain and where the phenomena of stress release is very common together with the uncertain monsoon winds make the region highly prone to natural disasters. The region being the most populous in the world further add to the damage caused by the natural disasters.

Drought, Floods, Cyclones , landslides and Earthquake are the major types of disaster phenomena occurring in the region. Almost all parts of India experience one or more of these disasters. Based on the frequency of occurrence and vulnerability to natural disasters, the entire country may be classified into three broad categories. The first is the Himalayan region spreading over 500000 square km. This region is prone mainly to Earthquakes,, Landslides, Avalanche and bush fire. The second category is the north and central Indian Plains. The region is having some great river systems and a rich source of water for drinking and irrigation. However, these rivers, during the monsoon period usually carry water in excess to their capacity causing flood phenomena. The same region also experiences droughts when the rainfall is less. The third category is the great coastline of India which is prone to devastating cyclonic winds emerging in the oceans. Under NRDMS Programme, thrust is being given to incorporate studies on landslides, drought and flood.

LANDSLIDES :

Landslides occur in the hilly terrain. The Himlaya being geologically young and susceptible to earthquakes and intensive soil erosion, is highly prone to occurences of landslides. Landslides also occur in Western Ghats, Eastern Ghats and Nilgiri hills with lesser frequency and intensity. Over the years, due to increasing cultural activity, the incidences of landslides have shown a disturbing tend of occurrence with higher damage to life and property. In 1998, some of the worst occurrences of landslides were witnessed. International experience, e.g. Japan, Hongkong, and USA, has shown that proper management of slopes on sound scientific principles can lead to mitigation of landslide hazard to a large extend. In India, landslide studies are conducted by a number of institutions, research and academic. However, there is a need for better coordination among a various research groups so that a focussed thrust can be provided to some critical aspects of landslide studies, for example geotechnical characterisation, soil mechanics and landuse zonation. The Department of Science & Technology has initiated a coordinated programmed on the Study of Landslides which is being carried out in a multi-institutional mode. The various topics of research on which some projects have been initiated are;
* Database

* Development
* Zonation

* Monitoring and instrumentation
* Modelling and upgradation of technology
* Documentation and dissemination
* Training

Intensive test areas:

Detailed investigations of geological studies have been undertaken in the parts of SatlujBeas Valley, H.P., South Sikkim, Parts of Garhwal and Kumaon Himalaya, Western Ghats, Nilgiri's Hill, Lungeli District, Mizoram and Guwahati, Assam (Fig.1) during the last years.Recently, five more critical slopes/landslides have been identified by the Task force of Landslides for detailed geological sand geotechnical investigations. The identified landslides will also be monitored with a suitable set of instrument. The names of the new landslides are: Chanmari (Sikkim), Sher-ka-Danda (Nainital), Nathpa (H.P.), Powari (H.P.) and Karsingsa (Arunachal Pradesh).

Present Status: A few of the improtant outputs of the programme are:

1. Landslide Hazard Zonation Methodology: Identification of areas prone to landslide and their cateogrisation as per the intensity of the disaster are the key elements in suggesting mitigative measures for minimsing the losses caused by landslides. Experience gained during the studies undertaken by WIHG, CBRI, CRRI and Roorkee University in different selected test areas have helped in evolving a landslide hazard zonation methodology. Based on this methodology, landslide hazard zonation mapping has been completed in parts of the Satluj-Beas Valley, H.P., Garhwal Himalaya, Kumaon Himalaya, Sikkim, Nilgiri's, Lungeli, Guwahati and Western Ghats on 1:50,000 scale. Also, micro zonation on 1:10,000 scale was carried out in parts of Srinagar-Badrinath Road in Garhwal Himalaya.

2. Mass Movement Model: In order to quantitatively assess the extent of mass movement and predict the deposition profile in case of a landslide, it is necessary to model the process of the mass movement and analyse the slope stability. Digital terrain models were used in a study undertaken by IIT, Mumbai to prepare the sections of the unstable slopes and determine the failure surfaces. The mass movement was modelled to predict the motion parameters and deposition profile.
3. Control measures: A state-of-the-art report on landslide control measures was prepared. The other work such as stablisation of landslide through soil nailing technique is in progress.
4. Dissemination and training: In order to create an awareness among the potential users, four training courses/workshops have been conducted during the last five years.
5. Future Thrust: Responding to the incidences of landslides in Himalayan region during the month of August, 1998, in which major damage to life and property occurred, the DST convened a meeting on 15th September 1998 under the chairmanship of the Secretary, DST to review the scientific status of the landslides studies in the country. Suggestion have emerged for taking up short-term and medium to long term follow-up measures. Nothing the inputs provided by various institutions, the following Task Forces were suggested to be constituted:

Landslides Hazard Zonation - by GSI

Geotechnical Investigations - by DST

Landuse Zoning and Regulations - by D/o Envi. & Forests

Following up the above recommendation, DST has constituted a Task Force on "Geotechnical Investigations on Landslides" in November, 1998. This Task Force held four meetings so far. Five landslide sites have been selected for detailed geological and geotechnical investigations. The names of the selected landslides are" Powari (H.P.), Sher--ka-Danda Slide (Nainital, U.P.) Chanmari (Sikkim), Karsingsa (Arunachal Pradesh) and Nathpa Landslide (H.P). All the slide areas are proposed to be suitably instrumented for monitoring of the landslide movements.