Occurrence of Ground Water in Hard Rock Under Distinct Geological Setup

Abstract

Groundwater movement and its properties are unique with reference to its place of occurrence. Karnataka State can be considered as having three major hydrogeological provinces Viz. Archaean crystalline province, Metamorphosed sedimentary province, and Deccan Trap province. Ground water occurs in these provinces under unconfined to semi-confined conditions and under confined conditions in depth. The rock units in these provinces do not have the primary porosity, therefore, the occurrence and movement of ground water is through secondary porosity developed from the weathering and structural deformity undergone by the rocks. Hence, a study of ground water occurrence in two distinct geological setups i.e. Deccan Trap terrain of Eocene to Upper Cretaceous age (Afzalpur taluk) andPeninsular Gneissic terrain of pre-Cambrian age (Hassan district) has been attempted. Afzalpur taluk, Gulbarga district is underlain by basalts and followed downwards by Shale and Limestone. Ground water accounts 88% of the net area under irrigation and is the only dependable source for domestic, agriculture and industrial sectors. As per the Dynamic Ground Water Resources Estimation (2009), Stage of ground water development in the taluk is 94% and is categorized as ‘Critical’. Under Ground Water Exploration programme during the year 2010-2013, 21 bore wells were constructed up to a depth of 300 meters in the taluk at different locations.Hassan district is underlain by peninsular gneiss, granites and schists. Ground water accounts 27% of the net area under irrigation. As per the Dynamic Ground Water Resources Estimation (2009), Stage of ground water development of the district is 46% and is categorized as ‘Safe’. Under Ground Water Exploration programme during the year 2010-2011, 18 bore wells were constructed up to a depth of 200 meters in Channarayapatna, Hassan, Alur and Belur taluks of Hassan district at different locations.Data collected during the drilling and post drilling were analysed and compared to decipher the occurrence of ground water in different geological setups. The analysis shows that the BGC forms a better aquifer as compared to the Basalts.