A Geographical Information System (GIS) is devised to capture, store, manage, display and analyze spatial data which enables users to utilize geographical information for various applications. It performs as a viable tool to conceptualize spatial data and assist in building decision support systems for organizations. Data stored in GIS is stored as points, lines, polygons and raster images. What makes GIS special and effective is the use of spatial indices which make it possible to identify multiple features in any random region of a map. GIS is more than just a tool as people and methods are combined with geospatial software and tools to enable spatial analysis, managing large datasets, and the display of information in a map/graphical form. GIS has many applications, one of which is classifying danger zones for landslide hazard.
Natural Resources Data Management System (NRDMS) was launched in 1982 by the Department of Science (DST) to develop and demonstrate the methods and techniques for spatial planning at district or sub-district units. Over the last three decades, NRDMS has constantly evolved with the advancement in technologies for Data Capturing, Sharing, and Analysis of Geo-Spatial Data.
Landslides occur due to a wide range of ground movements such as during earthquakes that lead to failure of the slope, debris flows, rockfalls and other various kind of mass movements. Unlike popular notion, landslides can occur underwater as well and the phenomenon is known as a submarine landslide. Landslides primarily occur due to the force of gravity but many factors build up specific surface conditions that make the slope area prone to failure. Landslides pose a grave danger to both human life and property due to their treacherous nature. Landslides underwater can even cause tsunamis which attain a height of several metres. The latest of which is a tsunami due to a landslide which killed 4 people while washing away 11 homes in Greenland in July 2017 (Fritz, 2017).
12.6 per cent of land in India (excluding snow covered area), which amounts to over 0.4 million sq.km is prone to landslide hazard. Out of the landslide-prone areas, 40 per cent fall in North East region of the Himalayas which includes Sikkim and Darjeeling; 33 per cent fall in North West region of the Himalayas which includes Uttarakhand, Himachal Pradesh and Jammu & Kashmir; 20 per cent falls in the Western Ghats and Konkan Hills area which includes Tamil Nadu, Maharashtra, Kerala and Karnataka and 2 per cent in Eastern Ghats of Aruku area in Andhra Pradesh (GSI, 2016). India has struggled with a fair share of landslides in the past, the recent example being the 2014 landslide of Malin, Pune, Maharashtra which took the lives of over 150 people (GOI, 2014). Every year, hundreds of people lose their lives to landslides and the increased population density is only adding to the danger.
Landslide Hazard Analysis
Landslide hazard analysis and danger mapping includes the mapping of potential landslide areas and categorising it into different zones based on the vulnerability. It is used to identify the factors that are in direct correlation with landslides, estimate the relative contribution of factors which cause slope failure and establishing a relationship between the factors and landslides which helps delineating the landslide hazard zones. It can prove vital in reducing the loss of human life during catastrophic events and can aid in the development of guidelines for sustainable land-use development.
Geographical Information System is an appropriate tool as it collects, stores, manipulates, displays and analyses huge spatial data fast and effectively. Several factors are used for this kind of analysis, which include geology, land use/cover, geomorphology and hydrogeology. The sub-factors that are used by the GIS software include:
- Aspect of a slope
- Curvature of a slope
- Major Thrust/fault
- Land Use/ Land Cover
- Slope Forming Material
These features together contribute towards landslide hazard analysis to assist in assessing susceptibility of slopes towards landslides (Bhowmick and Ghosh, 2014).
Landslide mapping in India using GIS has brought forward many results in certain landslide-prone regions. One such mapping was done in Mandakini valley, Rudraprayag, Uttarakhand by the Geological Survey of India. Using the mapping, certain susceptibility zones were classified based on the possibility of landslides in the particular area.
Courtesy: Geological Survey of India
As shown in the GIS map model, the red zones are high susceptibility classes where landslide probability is the highest. 8 per cent of the area mapped (Mandakini valley) is classified as highly susceptible. The Badasu Rampur area, which witnessed landslides in 2013, is classified under the red zone. The villages in the area are threatened by the retrogressive movement of the active debris slides caused by the erosive effect by Mandakini River. Red zone on upstream of Gaurikund on both sides along Mandakini River is prone to landslides due to similar erosion effects as the Badasu Rampur area (Howmick & Ghosh, 2014).
GIS has allowed government bodies to successfully analyze the dangers posed to habitat in the susceptible zones which can result in measures to mitigate the effects of these disasters. GIS may not be able to prevent these catastrophes but their effects can be minimized to continue the smooth functioning of habitats in these areas.
The accuracy of landslide risk estimation depends solely on the quality and the quantity of the input parameters. The availability of information of previous landslides is crucial for the assessment of elements at risk. Due to the limited availability of complete and accurate data on previous damages, risk assessment becomes highly subjective. To be able to completely assess landslide risks, all government agencies, networks and local bodies are required in unity. Nevertheless, in the present work, the analysis helps in identifying high-risk zones in an area. This not only helps in understanding the situation at the ground level, but a detailed analysis can also result in guiding construction activities curbing the loss of property and human life.
GIS is molding spatial data management in education, health, agriculture, tourism and many more aspects of our daily life. The landslide mapping of Mandakini valley, Uttarakhand is one of many activities GIS has been integrated into. Crime mapping by the Delhi Police, Asset Mapping of each state, Public Toilet Utility Mapping and Coal Mining surveillance are some of the many projects which prove that GIS is a successful tool for the government to employ for the betterment of society.