Assessment of Urbanization Impacts on Coastal Aquifer Vulnerability by Seawater Intrusion Using GIS-Based Modified GALDIT-B Model: A Case Study of South Chennai Coastal Region, Tamil Nadu, India.

Abstract

Seawater intrusion into groundwater aquifers is a growing global concern due to factors such as groundwater exploitation, rising sea levels, and climate change. This study focuses on the Chennai south coastal region and incorporates an urban sprawl perspective to delineate vulnerable zones of seawater intrusion into littoral aquifers. The study uses land use/land cover (LULC) classification to measure the expansion of impervious surfaces in the region from 2000 to 2020. The GALDIT-B model is modified and performed using the Geographic Information System (GIS) based -Analytical Heirarchy Process (AHP) to assign weights and ratings to each factor. The resulting model identifies five categories of vulnerable zones, ranging from very high to very low, based on factors such as groundwater level and the impact of existing seawater intrusion. The study found that the coastal and deltaic geomorphological formations in the region, which consist of clayey and sandy aquifer regions with built-up areas, are the most vulnerable to saltwater intrusion. The vulnerability of the very high vulnerable zone increased by 6% between pre-monsoon 2000 and pre-monsoon 2010 and by 16% between pre-monsoon 2010 and pre-monsoon 2020. The model was cross-validated using major hydrochemical parameters and the hydrochemical facies evolution (HFE) diagram of groundwater elements. The highest concentration of NaCl was found in the extremely vulnerable zones. The Piper trilinear diagram was used to identify the presence of saltwater in coastal aquifers. The modified GALDIT-B model is a useful tool for decision-makers involved in the development of coastal urbanization.