GIS-based slope-stability zonation for soil-slide hazard assessment in Kottayam, Kerala, India

Soil slides, induced mainly by slope instability, imply a critical localised hazard in terrains characterised by high monsoonal rainfall, undulating relief, and intensified human activity. Despite their localised extent, they could cause a significant socio-economic impact in Kottayam Taluk, one of Kerala’s densely populated taluks. Thematic layers derived from the ASTER GDEM indicate that the taluk exhibits undulating topography with slope values ranging from 0° to 35°, and an increasing relief ratio towards the east, making it more vulnerable to slope failures. Although the drainage network, which forms part of the Meenachil River system, predominantly shows a dendritic drainage pattern, a perfect trellis pattern is developed towards the eastern part of the taluk due to the presence of lineaments trending NW–SE. In the study, a GIS-based heuristic ranking and weighting method is effectively integrated to prepare a stability zonation map of the Kottayam Taluk, using various geo-environmental factors such as slope, relative relief, drainage, lithology, rainfall, land use, and lineaments. The stability zonation map demarcates four zones: very stable, stable, moderately stable, and unstable. The moderately stable and unstable zones are concentrated at various localities of the east and central parts of the taluk. Adopting appropriate mitigative measures, developing community awareness of various geo-environmental factors that influence slope stability, and following scientific land-use practices are important to ensure long-term slope stability and reduce hazard risk and adverse socio-economic impacts of slope failures.