Active tectonics and its impacts over groundwater systems in the parts of Tamil Nadu, India

The relation between the fracture systems and the groundwater movement has been well demonstrated all over the world. Though studies have been carried out on the morphology, chronology and the dynamics of the fractures and their control over groundwater in hard rock aquifer systems, the role of active tectonics over groundwater has not been studied much and the groundwater has been targeted accordingly. In this connection, in the present study, database was generated on the annual mean water levels of 1800 observation wells for the years 1975, 1980, 1985, 1990 and 1995 from the state of Tamil Nadu, the overall mean water levels were worked out for the 5 years for these 1800 wells and digital elevation model was generated using GIS on such overall mean water level. The same indicated that groundwater levels occur as alternately arranged East-West trending elliptical domes/ridges and elliptical basins/valleys, from Cape Comorin in the south to Chennai in the north. Though these groundwater valleys and ridges broadly follow the cymatogenic arches and deeps, the groundwater valleys significantly coincide with Ramanathapuram and Chennai post collision East-West trending cymatogenic arches and the groundwater ridges coincide similarly with the cymatogenic deeps/grabens. The digital elevation models generated for the mean water level data individually for the above 5 years, for a test site in the parts of northern Tamil Nadu in proximity to Chennai arch region, indicated similar alternately aligned E-Wlocal groundwater ridges and valleys. The axes of these E-W trending groundwater ridge and valley features of 1975 gradually attained an hourglass shape in 1995 with the axes of the southern groundwater valleys attaining northerly convexity and the northern valleys the southerly convexity. In addition, the groundwater cone of 60 km radius seen amidst many groundwater valley features in the DEM in proximity to Chennai arch region appears to have gradually shrunk from 1975 to 1995. All these indicate that these are the reflections of ongoing tectonic arching and deepening due to the still active northerly to north north-easterly oriented compressive force which has originally drifted the Indian plate towards northerly. From this, it can be further surmised that instrument-based finer water level monitoring could give indications on active tectonics, from which not only potential groundwater zones can be located but also seismicities can be predicted.