LANSLIDE HAZARD ZONATION
The term zonation applies in a general sense to categorise the land surface into areas and arrange them according to degrees of actual or potential hazard from landslides or other mass movements on slopes (Varnes, 1984). The fundamental assumptions that are used in zonation studies are: the past and present are keys to the future, the main causative factors of landsliding can be identified and degrees of hazard can be estimated.
TERRAIN EVALUATION
Hazard zone mapping involves a detailed assessment and analysis of the past occurrences of landslides in terms of their location, magnitude and frequency with respect to various geo-environmental factors that influence landslides and mass movements. The factors that affect slope instability are varied and their interaction processes complex depending on terrain set up and climatic characteristics. The most important terrain evaluation factor in hazard zone mapping is the recording of the landslides that occurred in the area. The spatial distribution of old and presently active landslides when compared with different terrain factors reveal their importance as a causative sliding factor. The various individual factor maps such as landuse, soil thickness, relative relief, slope etc. have been prepared on 1:50,000 scale. However, the landslide population map and collection of data in field were done on a scale 1:25,000 using Survey of India topographic sheets as base maps. Data supplementation was done using remote sensing products

The terrain factors selected for hazard zonation and their respective Landslide Susceptibility Values are given below

Terrain factors and Landslide Susceptibility Values

Landslide Susceptibility Index (LSI)
After assigning landslide susceptibility values, a Landslide Susceptibility Index (LSI) is computed for all categories of each factor with a correlation of landslide percentage per km2 of that category and the LSV assigned to it. The LSI is calculated using the formula:
LSI = Landslides % per km² x LSV 100
Based on the cumulative LSI values obtained, the area was classified into 5 zones of relative instability viz. critical, highly unstable, moderately unstable, moderately stable and stable classes depending upon the range of cumulative LSI values

Critical zone
This is a very unstable zone where landslides are likely to occur in view of the prominent causative factors present. The area is almost degraded to such a state that it is practically impossible to evolve economically and socially acceptable remedial measures which can positively prevent recurrence of the hazard. The area has to be entirely avoided for settlement or other developmental purposes and preferably left out for regeneration of natural vegetation and attainment of natural stability in course of time through the physical processes active in the area. Highly unstable Zone
These areas are prone to landsliding. Terrain setting is comparable to the first category and in many cases the landslides initiated in the first category will have its impact on this zone also. The area needs urgent attention in the form of mitigatory measures like regeneration of natural vegetation, reforestation, drainage correction and restriction of seasonal tilling activity and contour bunding to ensure proper drainage etc. Unless immediate action plans are implemented this zone will soon deteriorate to the critical category. The settlement as far as possible is to be avoided and permitted only in localised safe areas.
Moderately unstable
These are areas which are stable in the present condition but future landuse activity is to be properly planned so as to maintain its present status. However, if natural drainage is disrupted/slope modified landslides could be triggered.
Moderately stable zone
For all practical purposes these areas are safe from mass movements by virtue of its present geoenvironmental set up. However, many slopes falling within this zone could be destabilised by uncontrolled erosion, improper landuse practices and development activities.
Stable zone
A very stable zone where no restrictions are warranted as reasonable human activity of any form do not possibly threaten the balance.
HAZRAD ZONATION MAP
The Hazard Zonation Map of the study area indicates that the unstable areas are confined mainly to the plateau edges and adjacent dissected hill sections while the midland and plateau region are stable. In terms of aerial distribution, the high risk areas (critical zone) is only 4.39 sq.km making 0.58% of the total area. The highly unstable zone covers 27.05 sq.km forming 3.58% of the total study area. These are the two zones which warrants immediate action in terms of mitigatory measures and restriction of activities which accelerate further deterioration of the terrain set up.