Integration of remote sensing data and the geographical information system (GIS) for the exploration of groundwater resources has become a breakthrough in the field of groundwater research, which assists in assessing, monitoring, and conserving groundwater resources. In the present paper, various groundwater potential zones for the assessment of groundwater availability in Theni district have been delineated using remote sensing and GIS techniques. Survey of India toposheets and IRS-1C satellite imageries are used to prepare various thematic layers viz. lithology, slope, land-use, lineament, drainage, soil, and rainfall were transformed to raster data using feature to raster converter tool in ArcGIS. The raster maps of these factors are allocated a fixed score and weight computed from multi influencing factor (MIF) technique. Moreover, each weighted thematic layer is statistically computed to get the groundwater potential zones. The groundwater potential zones thus obtained were divided into four categories, viz., very poor, poor, good, and very good zones. The result depicts the groundwater potential zones in the study area and found to be helpful in better planning and management of groundwater resources. ª 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.

A morphometric analysis was carried out to describe the topography and drainage characteristics of Papanasam and Manimuthar watersheds. These watersheds are part of Western Ghats, which is an ecologically sensitive region. The drainage areas of Papanasam and Manimuthar watersheds are 163 and 211 km 2 , respectively and they show patterns of dendritic to sub-dendritic drainage. The slope of both watersheds varied from 0°to 59°and 0°to 55°, respectively. Moreover, the slope variation is chiefly controlled by the local geology and erosion cycles. Each watershed was classified as a fifth-order drainage basin. The stream order of the basin was predominantly controlled by physiographic and structural conditions. The increase in stream length ratio from lower to higher order suggests that the study area has reached a mature geomorphic stage. The development of stream segments is affected by rainfall and local lithology of the watersheds.

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The present study was carried out to decipher the groundwater potential zones in the coastal terrain of Tuticorin using Indian remote sensing satellite IRS-1C, LlSS-III data on a 1:50,000 scale and Survey of India (SOI) toposheets. The thematic layers such as lithology, slope, land-use, lineament, drainage, soil and rainfall were generated and integrated to prepare the groundwater prospect and recharge map of the study area. These layers were transformed to raster data using feature to raster converter tool in Arc GIS 9.2 software. Subjective weights are assigned to the respective thematic layers and overlaid in GIS platform for the identification of potential groundwater zones within the area. These potential zones were categorized as ‘high’, ‘moderate’, and ‘low’ zones with respect to the assigned weightage of different thematic layers. The resultant map shows that 10% of the area has highest recharge potentials, this is due to the percolation of precipitated water into the sub-surface rocks, followed by 65% of the area with moderate groundwater recharge potentiality, and rest of the area has low recharge potential. The study highlights that the total average annual precipitated water (877 mm) is responsible for natural recharge of the aquifers in the Tuticorin area.

Geochemical signatures of groundwater in the coastal aquifers of Kadaladi block of Ramanathapuram District, Tamilnadu, India were used to identify the chemical processes that control hydrochemistry. The parameters such as pH, EC, TDS and major ion concentrations Na, K, Ca, Mg, Cl, HCO 3 , SO 4 , PO 4 and NO 3 of the groundwater were analyzed. Abundances of these ions are in the following order Na [ Ca [ Mg [ K and Cl [ HCO 3 [ SO 4 [ NO 3 [ PO 4 . Na-Cl is the dominant hydrochemical facies of the study area. Interpretation of the hydrochemical data suggests that hydrochemistry of the study area is controlled by mixing of fresh water with relict saline water, ion-exchange processes, silicate weathering and evaporation are responsible for the groundwater chemistry of the study area. Above statement is further supported by Gibbs plot where most of the samples fall within the evaporation zone. Good quality groundwater is restricted to coastal sand dunes running parallel to the coast and it is important to conserve these dunes.