STUDY . OF SEAWATER INTRUSION IN COASTAL AQUIFER OF MINJUR AREA, NORTH OF CHENNAI

Abstract

Coastal aquifers are always at high risk of contamination due to sea water encroachment. Indiscriminate pumping from the coastal aquifer is the major cause for massive encroachment of sea water into the aquifer. Hence planning, for the sustainable ground water development in the coastal aquifer is very much essential. Minjur aquifer on the coast of Tamil Nadu, north of Chennai, is a highly potential confined aquifer, which is subjected to indiscriminate pumping by farmers and also by Minjur wellfield to augment city water supply. These large scale pumpings have resulted in progressive lowering of the piezometric level, well below the mean sea level and the hydraulic gradient has been created towards land. Consequently seawater has intruded into this important ground water resource of the area. In the present study, the hydrogelogical data of Minjur area, have been analysed to understand the nature of Minjur aquifer system and to asses the impact of large scale pumpings on the piezometric levels. The water quality data have been used to study the spatial and temporal variation of salinity in the minjur confined aquifer and to study the movement of freshwater-seawater interface. The ground water flow of the study area has been modelled to simulate the piezometric heads distribution under different pumping strategies. A grid of 12x24 cells has been designed and the model has been calibrated under transient conditions in two stages (i.e. for nonmonsoon period and monsoon period of 1988). The model is then verified using data of periods Feb. to Sept. 1997 and Oct. to Dec. 1997. Subsequently, projection runs have been performed with various stipulated pumping patterns.