S. Anbazhagan

Landslide Hazard Zonation Mapping in Ghat Road Section of Kolli Hills, India

Landslides are the most common natural disaster in hilly terrain which causes changes in landscape and damage to life and property. The main objective of the present study was to carry out landslide hazard zonation mapping on 1:50,000 scale along ghat road section of Kolli hills using a Landslide Hazard Evaluation Factor (LHEF) rating scheme. The landslide hazard zonation map has been prepared by overlaying the terrain evaluation maps with facet map of the study area. The terrain evaluation maps include lithology, structure, slope morphometry, relative relief, land use and land cover and hydrogeological condition. The LHEF rating scheme and the Total Estimated Hazard (TEHD) were calculated as per the Bureau of Indian Standard (BIS) guidelines (IS: 14496 (Part-2) 1998) for the purpose of preparation of Landslide Hazard Zonation (LHZ) map in mountainous terrains. The correction due to triggering factors such as seismicity, rainfall and anthropogenic activities were also incorporated with Total Estimated Hazard to get final corrected TEHD. The landslide hazard zonation map was classified as the high, moderate and low hazard zones along the ghat road section based on corrected TEHD.

Geomorphic appraisal of landslides on the windward slope of Western Ghats, southern India

The Western Ghats, the bold westerly escarpment of India paralleling the west coast, are characterized by different geologic and geomorphic units formed during different episodes of Earth’s history. The majority of these present day landforms evolved in response to the tectonic activity that the Western Ghats witnessed during the Tertiary period. The major structural features together with the geomorphic units have predominant role in the occurrence of cataclysmic landslides which the windward slope of Western Ghats witness during the peak monsoon season. The Kerala and Periyar lineaments, which are the sites of minor earthquakes, pass through the study area. Escarpments and structural hill systems are the vulnerable landforms for landslide occurrence. Due to the predominant role of these tectonic and geomorphic features in the capricious change of landforms, a study was carried out in this hilly terrain based on geomorphology. The study of soil, slope morphometry, relative relief, land use/land cover and hydrogeological conditions together with a multidimensional analysis in a GIS environment resulted in classifying the entire area into different landslide susceptible zones based on Bureau of Indian Standards. Moreover, the area is also divided into three zones based on the terrain conditions and the type of landslide occurrence. The methodology can well fit with any area experiencing the same terrain conditions and can be used to classify an area on the basis of landslide occurrence and geomorphology.

Groundwater sustainability indicators in parts of Tiruppur and Coimbatore districts, Tamil Nadu

The present study emphasizes the use of groundwater sustainability indicators, developed to assess the sustainability of the aquifer in Uppar Odai sub-basin located in part of Tiruppur and Coimbatore districts, Tamil Nadu. There are seven indicators discussed based on their relevance in groundwater sustainability. In most parts of the subbasin, groundwater development already exceeds 80% of the groundwater recharge. The results have shown that the sub-basin area has been contaminated with low hazard pollutant such as nitrate and fluoride. In addition, about 28% and 32% of the sub-basin area respectively is not suitable for irrigation. The analysis of water level data for the last 42 years has shown decline in water table. However, the water level condition has improved in the recent years due to water conservation measures. The basin requires necessary groundwater planning and management to maintain sustainable aquifer condition.

Electrical resistivity survey and shallow subsurface geological study in hard rock terrain, Southern India

The shallow sub-surface condition of the hard rock terrain is highly heterogeneous and it requires investigation of geology at close interval. The purpose of the present work is to interpret the shallow sub-surface geology to a limited depth (<100m) and to reveal the thickness of the various layers through electrical resistivity survey. In this context, the Nallampalli block located in Dharmapuri district, Southern India is selected. The area is mostly covered by gneissic and charnockitic rocks. In addition to resistivity survey, well inventory data was also collected from field investigations. The thickness of various sub-surface layers such as weathered zone, partially weathered zone, fractured zone and depth to bedrock were estimated. The estimated thickness and resistivity values were correlated with well inventory data. The average resistivity values for weathered, partially weathered, fractured and massive formations in the block are 55Ωm, 96Ωm, <303Ωm and >400Ωm respectively. The average depth to massive rock in the block is 38m below ground level (bgl). Remote sensing data were utilized to assess the sub-surface condition to a limited extent. The results obtained from the electrical resistivity survey and well inventory data have appreciable correlation.

GIS Based Quantitative Geomorphic Analysis of Fluvial System and Implications on the Effectiveness of River Basin Environmental Management

Rivers are sensitive to changes in tectonic deformation, and adjust themselves on different scales of time periods depending on the physical properties of the host rocks and climatic effects. The resultant changes are exhibited by the geomorphic indices and landform assemblages within a river basin. This paper presents the results of integrated quantitative geomorphic analysis conducted for understanding the prevalent tectonic activities in a medium sized drainage basin, the Thoppaiyar sub-basin, India. The major part of the study area is covered by gneisses and granites. The sub-basin is divided into fourteen fourth order micro basins (FOMBs) for quantitative geomorphic analysis. Prior to quantitative analysis, longitudinal river profile and channel morphology were studied. The channel morphology includes cross sections, width-to-depth ratio, entrenchment ratio, bank height ratio were measured during field investigation. Various geomorphic indices namely, the basin shape index (Bs), drainage basin asymmetry factor (Af), hypsometric integral (Hi), hypsometric curve (Hc), valley floor width-to-height ratio (Vf), transverse topographic symmetry (T) and stream length gradient index (SL) were derived using topographic maps and SRTM satellite data. The spatial distributions of these parameters were represented as thematic layers using. The results obtained from these indices were combined by ArcGIS 9.3 software to generate an index of relative active tectonics (IRAT) in the sub-basin. It indicated the prevalence of differences among the FOMBs and an overall relatively low tectonic activity in the Thoppaiyar sub-basin.