Hydrogeology of Madras City Aquifers

Subsurface lithological mapping has shown the presence of a crystalline rock ridge along the east coast of Madras City, and the aquifer above this ridge shows some characteristic features distinct from those on the western side. The presence of a fresh water ridge along the coast has checked the intrusion of sea water even though water levels are as low as 3m below mean sea level at certian places. Several pockets of brackish ground water have been identified which have been established as due to the presence of tanks and depressions therein. Identification of marine sands below the alluvium in some places gives an idea of the marine transgression that had occurred during Tertiary periods. Studies indicate that most of the alluvium is of estuarine origin, and that the crystalline ridge along with part of the east coast may be updergoing slow uplift.