Hydrogeology of Hard Rock Aquifer System - A Case Study from Turinjahalli Watershed, Dharmapuri District, Tamilnadu, India

Abstract

Hydrogeology hard rock aquifer system is very complex and the occurrence and movement of groundwater mainly controlled by secondary porosity developed from the weathering and structural deformity undergone by the rocks. The study area forms part of the poly-metamorphic and multistructural Archaean complex is underlain by crystalline formations consists of charnockite and hornblende biotite gneiss. There are major aquifer units delineated in the watershed based on the aquifer parameters and water level behaviour. The aquifer units are weathered aquifers and fractured aquifers, depth of weathered and fractured aquifers in the study area ranged between 2 to 29 m and 29 to 185 m respectively. The weathered aquifer contains water during monsoon season and becomes dry whereas the fractured aquifers yield water and four to five sets of fractures encountered in the aquifer system. 103 monitoring stations were established for groundwater level monitoring and carried out pre- and post-monsoon water level measurements. The depth to water levels in observation wells tapping aquifer during pre monsoon ranged between 10.90 m.bgl and 25.30 m.bgl and during post monsoon ranged between 12 and 31.20 m.bgl. The water table elevation map was prepared using the reduced levels for the monitoring stations to know the groundwater flow direction in the watershed. The map reveals that groundwater flow direction is from south-west to east/north-east direction. Based on Darcy’s equation, the rate of flow of groundwater in the aquifer system depends on the hydraulic gradient and hydraulic conductivity. The total amount of groundwater flowing through aquifer system in the watershed is 4.36 cubic meters per second.