Figure 1: Study Area Study area (Fig. 1) is located in the Dindigul district of Kodaikanal hill, which is a mountainous terrain in the Western Ghats of Tamil Nadu, with an area of 1039.46 km2. It is geographically located between 77° 14’ 26” and 77° 45’ 28” E longitudes and 10° 6’ 25” and 10° 26’ 54” N latitudes. n the survey of India toposheet, it forms part of 58 F/7, 8, 11 & 12 on 1:50,000 scale. It is widely hailed is the “Princess of Hill Stations” owing to the popularity it gained during British Raj. The climatic condition of the study area is characterized by humid conditions. Relative humidity is high during etreating north-east monsoon season (October to mid December). The mean temperature of Kodaikanal taluk is 5.93° C with a mean summer (June, July and August) emperature of 17.29" C and mean winter (December, January and February) temperature of 14.10’ C. The average annual rainfall is 1436.87 mm. The study area is fully covered by hills. The plain area forms a small part. = Table 1: Ranking for Stream frequency Slope Figure 2: Methodology flow chart The base map was prepared using toposheet nos. 58 F/7, 8, 11 and 12 on 1:50,000 scale. Spot height map have been used for he preparation of slope map, relative relief map and drainage map. The Indian Remote Sensing (IRS)-P6 Satellite Linear mage Self Scanning (LISS) - 4 sensor data of 4 May 2006 were purchased and registered based on Survey of India SOI) topographical sheets in the ERDAS software version. 9.3. Digital image interpretation techniques were followed for delineation of geomorphology, land use / land cover map. Since this study is concerned with the use of GIS methods to identify potential landslide zones, it involves the generation of thematic maps related to the causative factors. These thematic maps are in turn assigned ranks and weights and then analyzed in GIS domain. The methodology is summarized in Fig.2. Figure 3: Stream Frequency — Spatial Distribution Map Figure 5: Slope aspect Figure 4: Slope — Spatial Distribution Map Figure 6: Relative relief - Spatial Distribution Map The maximum elevation is 2517 m in the study area. Landslide events increase significantly with the relief of medium category 300 to 500 m (Fig.6) and is given rank 4. In relative relief, the Medium Category (300 — 500 m) is more prone to slides followed by High (> 500 m). The ranking of elevation is shown in Table 3. Table 5: Ranking for Landuse/landcover Table 4: Ranking for Landforms Figure 7: Geology - Spatial Distribution Map ine Huvio-denudational geomorpnological processes are actively involved in landscape reduction processes at upper reaches. These are in the form of plateau composed of charnockite rocks. Dissected typical stream carved morp radiating eroded ridges along Plateau portions represent a hology comprising of crested the down slopes. The cluster of hills is characterized by rill and gully erosion, smooth and rounded hilltop. The heigh decrease progressively along of the ridges was found to eastern side of the study area, signifying intense linear head word stream erosion and slope retreat under high hydraulic gradients of streams. These plateaus occupying nearly 24.84% of total geographical area are highly susceptible to severe erosion hazards. Pediments are broad gently sloping erosion surface are plain of low relief, in an arid or semiarid region at the base of an abrupt and receding mountain front; it is underlain by bedrock this pediment are occupying nearly 8.41% of total geographical area. Structural hills have been identified in almost all the study area and are delin eated based on the image characteristics viz. valley fills are delineated with the help of satellite image. It is having more vegetation. The valley fills cover in small areas. The composite slopes are also identified. From the ranking awarded above it may be seen that the geomorphological unit ‘Structural Hill’ and Pediment is more prone to slides than any other unit. Fig. 8 and the ranking of Landforms is show as Table 4. Figure 8: Landform Spatial Distribution Map Figure 9: Landuse/landcover- Spatial Distribution Mar In Landuse and landcover the categories Mixed Plantation, Open to Dense Forest has all the slides while Mixed Cultivation, Scrubland, and Rural Settlements have none. The ranking of landuse/landcover is show as Table 5. Figure 10: Spatial Queries in High landslide Hazard zones Table 6: Landslide Hazard Zone (LSHZ) in the Study Area Acknowledgements
