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The study area can be broadly divided into three zones - The plateau region, midland and a middle zone consisting of the plateau edge and adjoining dissected hill region.
This zonation is broadly applicable for the entire Western Ghats region falling within Kerala.
The landslide hazard is mainly confined to the plateau edge and adjacent dissected hill region.
Out of the 756 sq.km covered in the study, about 0.58% (i.e. 4.38 sq.km) falls in the high risk zone (critical zone) and 3.58% (i.e., 27 sq.km) in the highly unstable zone. These areas warrants immediate action plans in terms of mitigatory measures.
In the study area of 756 sq.km only <6% of the area can be categorised as in one way or other susceptible to landslide hazard.
The most prevalent and disastrous type of landslide in the area are debris flows (Locally known as Urul Pottal). Such mass movements affect only the overburden and leaves the underlying crystallines intact.
Slope, overburden thickness and landuse are the most important parameters influencing mass movements while for deciphering critical areas, drainage (pattern and density) relative relief and landform set up offer excellent clues.
A common factor noticed in most of the landslide prone areas is deforestation or degradation of natural vegetation in the recent past.
Slope of the terrain is a crucial parameter determining slope stability. Slope magnitude, length and direction are relevant factors determining slope stability. Slopes above 16o with length more than 150 m are to be evaluated with caution especially in the plateau region and dissected hill sections. There seems to be a preference for landslides in slopes running in SW direction.
Among landuse types the areas with degraded natural vegetation shows maximum slide intensity. Generally such areas fall in the upper slopes.
In many instances contour bunding adversely affect slope stability by preventing storm water drainage during heavy rains.
Indiscriminate construction of sediment check dams at slope breaks especially in vulnerable sections of slopes leads to overloading and excessive lateral infiltration of water leading to instability.
Relative relief is an important parameter which can be applied for landslide hazard zonation. High landslide population is seen associated with a relative relief of 200-400m within the plateau edge and dissected hill region.
Maximum incidence of landslides within the study area is associated with the parallel pattern of drainage.
On an overall assessment it is inferred that a two day rainfall in excess of 300 mm could trigger a landslide in a vulnerable slope provided that the sub soil is already saturated.
Socio economic survey indicates that within the two landslide affected areas viz., the upper catchment of Minachil and Manimala rivers, hardly 30% of the total land is owned by local settlers while 70% of the area is within large scale private estate, revenue land and forest land
Majority of the settlers own <2 acres of land (90%) and fall within the low income group assessed from their type of dwelling houses and other resources available to them.

Natural Hazards Management
Coastal Erosion		Landslide		Earthquake	Lightning	Radioactivity	Flood	Drought

Introduction	EVALUATION STUDY IN TERMS OF LANDSLIDE MITIGATION IN PARTS OF WESTERN GHATS KERALA (A project Sponsored by Ministry of Agriculture, Govt. of India)
Study area
Methodology
Parameters
Landslide Hazard Zonation
Socio-Economic Evaluation
Conclusions
Recommendations
IMPORTANT CONCLUSIONS The study area can be broadly divided into three zones - The plateau region, midland and a middle zone consisting of the plateau edge and adjoining dissected hill region. This zonation is broadly applicable for the entire Western Ghats region falling within Kerala. The landslide hazard is mainly confined to the plateau edge and adjacent dissected hill region. Out of the 756 sq.km covered in the study, about 0.58% (i.e. 4.38 sq.km) falls in the high risk zone (critical zone) and 3.58% (i.e., 27 sq.km) in the highly unstable zone. These areas warrants immediate action plans in terms of mitigatory measures. In the study area of 756 sq.km only <6% of the area can be categorised as in one way or other susceptible to landslide hazard. The most prevalent and disastrous type of landslide in the area are debris flows (Locally known as Urul Pottal). Such mass movements affect only the overburden and leaves the underlying crystallines intact. Slope, overburden thickness and landuse are the most important parameters influencing mass movements while for deciphering critical areas, drainage (pattern and density) relative relief and landform set up offer excellent clues. A common factor noticed in most of the landslide prone areas is deforestation or degradation of natural vegetation in the recent past. Slope of the terrain is a crucial parameter determining slope stability. Slope magnitude, length and direction are relevant factors determining slope stability. Slopes above 16o with length more than 150 m are to be evaluated with caution especially in the plateau region and dissected hill sections. There seems to be a preference for landslides in slopes running in SW direction. Among landuse types the areas with degraded natural vegetation shows maximum slide intensity. Generally such areas fall in the upper slopes. In many instances contour bunding adversely affect slope stability by preventing storm water drainage during heavy rains. Indiscriminate construction of sediment check dams at slope breaks especially in vulnerable sections of slopes leads to overloading and excessive lateral infiltration of water leading to instability. Relative relief is an important parameter which can be applied for landslide hazard zonation. High landslide population is seen associated with a relative relief of 200-400m within the plateau edge and dissected hill region. Maximum incidence of landslides within the study area is associated with the parallel pattern of drainage. On an overall assessment it is inferred that a two day rainfall in excess of 300 mm could trigger a landslide in a vulnerable slope provided that the sub soil is already saturated. Socio economic survey indicates that within the two landslide affected areas viz., the upper catchment of Minachil and Manimala rivers, hardly 30% of the total land is owned by local settlers while 70% of the area is within large scale private estate, revenue land and forest land Majority of the settlers own <2 acres of land (90%) and fall within the low income group assessed from their type of dwelling houses and other resources available to them.