Integrated Study on Groundwater Dynamics in the Coastal Aquifers of West Bengal for Sustainable Groundwater Management

Abstract

Coastal zones are vital regions that support approximately 40% of the global population, serving as crucial hubs for economic activities, agriculture, and settlements. However, these areas are increasingly threatened by rapid urbanization, climate change, rising sea levels, and seawater intrusion. Coastal West Bengal, particularly in districts like East Medinipur, South 24 Parganas, and Howrah, is acutely experiencing these challenges, compounded by excessive groundwater extraction and pollution. Understanding the structure of the saline-freshwater interface is essential for assessing diminishing fresh groundwater reserves, the discharge of fresh groundwater into the sea, salt enrichment in inland aquifers, and pollutant discharge into the marine environment. This study provides a comprehensive assessment of groundwater and surface water quality, runoff potential, seawater intrusion, and the impacts of population growth. A robust methodology was employed, including the collection of archival data on surface water, groundwater, and aquifer characteristics, supplemented by field and laboratory investigations. Detailed analyses of hydrogeology, water quality, and isotopic composition were conducted to evaluate the dynamic interactions between freshwater and seawater in the region, aiming to deliver actionable insights for planners, decision-makers, and implementation agencies. Key Findings: 1. Rainfall and Runoff: The average annual rainfall in the study area was recorded at 1728 ± 293 mm, with significant spatial variation. Higher rainfall near the coast contributes to runoff, especially in watersheds like the Damodar River, where runoff percentages reached 52.53%. This data is critical for flood management and urban planning. 2. Groundwater Potential: The study identified four groundwater potential zones: very high (16.78%), high (53.48%), moderate (29.52%), and low (0.22%). Areas with flat or gently sloping terrain showed higher recharge potential, indicating suitable regions for sustainable groundwater extraction. 3. Water Quality: High salinity levels were observed in shallow aquifers near the Haldi River, with notable declines in bicarbonate levels at greater depths. Isotopic analysis confirmed significant seawater intrusion, emphasizing the urgency of managing groundwater extraction to prevent further degradation. 4. Seawater Intrusion: Population growth is accelerating seawater intrusion, particularly in densely populated areas like Kolkata and Howrah. Mapping seawater intrusion in relation to population density reveals high-risk zones requiring targeted management strategies. 5. Long-Term Water Quality Trends: From 2010 to 2022, groundwater salinity fluctuated, with some areas showing freshening trends while others, particularly Howrah and Kolkata, continued to struggle with high salinity. Heavy metal concentrations, including arsenic and manganese, exceeded safe levels, necessitating immediate intervention for public health.