SLOPE STABILITY EVALUATION IN AND AROUND KODAIKANAL TOWN, TAMILNADU

Abstract

In the recent times, land development is given top priority in view of ever expanding urbanization phenomenon. On the other hand, land conservation is an important aspect in order to preserve the already developed land categories. In this context, it is essential to understand the nature of hazard associated with urbanized land areas. This is particularly true in case hill towns such as Kodaikanal, in Tamilnadu where the expansion of the town limit is taking place without taking into consideration the inherent characteristics of the terrain. Land use suitability assessment is of great importance in order to protect the land from geological disasters, ecological risks, economic and human loss in such areas. The study area, Kodaikanal, referred as the "Princess of Hill stations", a small but popular hill station with an area of about 22 sq. km., is situated in Tamilnadu, India, was chosen as it is facing the onslaught of unplanned urbanization for the past about a decade and the consequent instabilities at many locations. In this study, slope instability assessment has been carried out by using preparing the landslide hazard zonation (LHZ) map of the area using Landslide Hazard Evaluation Factors (LHEF) rating scheme. This process helps to identify the landslide potential in different hill slope facets and particularly to identify high hazard and very high hazard zones. For that purpose, the basic causative factors such as lithology, structure, slope morphometry, relative relief, land use and land cover, and hydrogeological condition as well as external factors like seismicity and rainfall were used to classify the slopes into different landslide hazard zones. A total of 96 facets were delineated of which there are 73 are debris slopes and 23 are rock slopes. The LHEF ratings were given facet wise. From the prepared Landslide Hazard Zonation (LHZ) map, the facets falling under very high hazard zones were taken up for detailed analysis. For individual slopes falling in very high hazard and on debris materials, shear strength parameters were estimated from the samples collected from respective slopes, cross-sections were prepared across the hazard prone slopes and factor of safety (FOS) was calculated. It is observed from the stability analysis that the rock slopes are stable with FOS more than 1 while the talus slopes are only marginally stable under dry condition. Depending upon the extent of slope instability and taking into consideration the site conditions, suitable remedial measures have been suggested.