THE STUDY AREA
The area selected for the study comprise 750 sq.km area falls within Idukki and Kottayam districts of Kerala The area forms part of the highland region of Kerala encompassing within it the entire upper catchments of the Minachil and Manimala and part of the upper catchments of Periyar, Pamba and Muvattupuzha rivers. The region has all the physiographic components of typical vulnerable zone of Western Ghats. This area has experienced multiple slides in the recent past. The eastern part is occupied by the Pirmed plateau which has all characteristics of a natural planation surface. This plateau land form has considerable areal extent and is the regional southerly extension of the Wynad plateau and the Mysore plateau. The Minachil and Manimala rivers originate form this plateau edge and its first, second and third order tributaries flow down through the steep plateau margin. Generally the elevation difference averages to about 1000 m from the origin of first order streams to the confluence with the main Minachil or Manimala river which is a 6th order stream. Thus the central part of the area has the active youthful upper catchments of two streams the westerly oriented Minachil river and southerly oriented Manimala river. These two upper attachments are typical erosion zones upon which the river is engaged in active head ward erosion. The plateau margin presents youthful topography where denudational landforms are prevalent which constantly push the drainage divide towards east. Further, the same drainage divide separates some parts of the upper catchment of Manimala and Minachil rivers which were constantly headword cutting both sides of a divide. Thus the central part of the study area hosts a plateau margin which has all pre-requisites of an active erosion zone where the natural terrain set up is conducive to slope failure/mass movements. Towards west of this zone the area has a dissected topography where the elevation difference is hardly more than 100m falling in the highland region. The area can be classified as the foothill region which presents a composite denudational and depositional topography. The relative relief is low with very little mass movement history within the zone. Thus the area selected has all the three physiographic zones: the plateau land from, plateau margin with the source region of rivers and the lower midland plains facilitating their evaluation in terms of landslide potential.