Integrated seawater intrusion study of coastal region of Thiruvallur district, Tamil Nadu, South India

B. Gowtham,G. Johnson Babu,V. Arulprakasam,K. Vinodh,S. Senthilkumar

doi:10.1007/s13201-019-1005-x

Abstract

The groundwater is the main resource of water for irrigation activity in river lacking area. The freshwater–seawater interface in the study region that has existed 3 km away from the coast in the year 1969 has been found to be migrated to distance of 13 km from the coast during the year 2007 noticed by the Central Ground Water Board (Central ground water board’s district groundwater brochure, Thiruvallur district, Tamil Nadu, 2007). Integrated geochemical and geophysical techniques were carried out in the study area to decode subsurface geologic pattern and delineate the seawater–freshwater zones. Total numbers of 50 samples were collected from the entire study area and analyzed for major ions. The considerable samples are brackish scenery of groundwater water at low depth. Chadha and Piper’s plots categorize the coastal groundwater into Na–HCO3, Ca–Na–HCO3, Ca–HCO3, and Na–Cl water facies, with Ca–HCO3 as the dominant. Cl/CO3 + HCO3 ratio, Cl/HCO3, and ionic strength, Mg/Ca and Cl/HCO3 ratios show that most of the samples in the study area are affected by seawater intrusion, which is also confirmed by the geophysical method. The results of vertical electrical sounding carried out in the study area reveal the low transverse resistance and high longitudinal conductance. It suggests the brackish nature of the groundwater in the eastern part of the study area may be due to the seawater intrusion. The final map using GIS platforms productively delineates the location that is really undergoing seawater and freshwater zone is migrated toward the inland. The article suggested further studies to arrest the migration of sea/freshwater interface into the land and avoid overexploitation of groundwater to further development.

Highlights

Coastal regions are generally vulnerable to seawater intrusion especially in regions where groundwater is overpumped
The study area that falls in the coastal region of Arani–Korattalaiyar river basin is situated between 13°00′N to 13°35′N latitude and 79°55′ to 80°25′E longitude enclosed by Indian Toposheets No 66 C 4, 66 C 3, 66 C 8 and 66 C 7 (Fig. 1)
Regions having low iso-apparent resistivity (i.e., < 10 Ωm) occur along the southern coastal tract extending up to central portion which clearly confirms the presence of saline water at various depths below the ground level

Summary

Introduction

Coastal regions are generally vulnerable to seawater intrusion especially in regions where groundwater is overpumped. The study area that falls in the coastal region of Arani–Korattalaiyar river basin is situated between 13°00′N to 13°35′N latitude and 79°55′ to 80°25′E longitude enclosed by Indian Toposheets No 66 C 4, 66 C 3, 66 C 8 and 66 C 7 (Fig. 1). It is surrounded in the eastern region by the Bay of Bengal, the Western region covered by Poondi reservoir, Southern part covered by Kancheepuram and Chennai districts, and state. A few isolated beaches of 100 to 500 m widths occur along the coast

Materials and methods

Results and discussion

Conclusion