Seawater Intrusion Assessment in Coastal Aquifers of Krishna District Using Hydro-Chemical Indicators and GIS Techniques (2020–2024)

Abstract

Groundwater in coastal areas is susceptible to salinization by the inland migration of seawater, driven primarily by excessive abstraction, reduced recharge, and hydrogeological imbalances of natural origin. This study evaluates the extent of seawater intrusion regarding the selected coastal belt using hydro-chemical indicators, geospatial analysis, and graphical interpretation. The quality data related to major cations (Ca²?, Mg²?, Na?, K?) and major anions (Cl?, HCO??, CO?²?, SO?²?) of groundwater were collected from the Central Ground Water Board, Government of India, with geographical coordinates. The sampling locations within a 40 km buffer from the coastline were considered for intrusion assessment. The chemical concentrations were converted into milliequivalents per liter (meq/L), and diagnostic ratios like Ca/Mg, Na/Cl, Cl/ (HCO?? + SO?²?), Cl/ (HCO? + CO?), and the Base Exchange Index (BEX) were computed to identify marine influence on groundwater. These indices provided a strong and multi-parameter method of intrusion detection. A Piper diagram, developed using RockWorks17 software facilitated visualization of hydro-chemical facies with clear distinctions between freshwater, mixed water, and saline water types. Sites affected by intrusion showed typical signatures like a decrease in the Na/Cl ratios, increases in the chloride-alkalinity ratios, negative BEX values, and shifts toward Na–Cl facies. Spatial mapping was carried out to demonstrate the geographical distribution of intrusion-impacted zones using ArcGIS. The intrusion map showed that areas near the coastline and low-lying coastal plains are highly affected, while inland areas are generally less affected. The present study of an integrated hydro-chemical, RockWorks17 based facies analysis and GIS-based approach has evolved into an effective framework for the identification of seawater intrusion and facilitates sustainable management of groundwater in vulnerable coastal aquifers.

Introduction

Groundwater is a vital resource in India’s coastal districts, but over-extraction has made these aquifers highly vulnerable to seawater intrusion (SWI), which increases salinity, degrades water quality, and reduces agricultural productivity. SWI is influenced by hydrogeological factors (aquifer geometry, tides, seasonal recharge) and human activities (over-pumping). Detecting intrusion relies on direct methods, such as hydro-chemical analysis of major ions and diagnostic ratios (Na/Cl, Mg/Ca, BEX) and graphical tools like Piper diagrams, and indirect methods, including geophysical surveys (ERT, VES, TEM) and GIS-based spatial mapping.

The study focuses on the Krishna District in Andhra Pradesh, a deltaic coastal area with intense groundwater use for agriculture and aquaculture, making it highly susceptible to SWI. Groundwater samples from 20 strategically selected wells within a 0–40 km coastal buffer were analyzed between 2020 and 2024. The methodology integrates hydro-chemical indicators, facies interpretation, and GIS-based spatial modeling to assess the extent, intensity, and temporal progression of seawater intrusion, identify high-risk zones, and provide a scientific basis for sustainable groundwater management in the region.

Conclusion

The present research work attempts an integrated approach for the evaluation of seawater intrusion within the coastal aquifers of Krishna District by adopting hydro-chemical indicators, Piper facies interpretation using RockWorks17, histogram analysis, and GIS-based spatial mapping. The multi-year assessment from 2020 to 2024 reflects a definite enhancement in the encroachment of saline water, mainly within the first 20 km from the coastline. Progressive increases in the diagnostic ratios of Cl/ (HCO?? + SO?²?), Cl/ (HCO? + CO?), and Na/Cl, coupled with negative BEX values, strongly establish the marine influence. The Piper plots indicate a clear evolution from Ca–HCO? freshwater facies to mixed and Na–Cl saline facies through time, suggesting both ion exchange and direct mixing with seawater. The spatial analysis reveals that the lower-lying coastal plains, aquaculture-dominated areas, and areas of high extraction of groundwater have been most affected. The study confirms seawater intrusion in Krishna District is active, expanding, and strongly controlled by anthropogenic pressures coupled with hydrogeological conditions. The integrated methodology adopted herein offers a robust framework for intrusion monitoring, early detection, and sustainable groundwater planning. The results clearly indicate the urgency of regulatory and scientific interventions to preserve the coastal aquifers from further salinization.

References

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Copyright

Copyright © 2025 Kareti Manikanta, Dr. P. Mynar Babu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.