COMPREHENSIVE ASSESSMENT OF SALTWATER INTRUSION DYNAMICS WITH ITS PLAUSIBLE FUTURE CONSEQUENCES CONCERNING CLIMATE CHANGE ALONG THE COASTAL AREAS OF COX'S BAZAR, BANGLADESH UTILIZING TIME-LAPSE ELECTRICAL RESISTIVITY TOMOGRAPHY

The existing complication of salinization in the aquifers of coastal areas in Bangladesh will worsen with the continuation of climate change in recent future. The shortage of drinking and irrigation water as the aftermath will lead to some irrevocable inconvenient consequences.

Utilizing the time-lapse electrical resistivity tomography (TL-ERT), this research is aimed at monitoring the dynamics of the saltwater intrusion in the coastland of Bangladesh (Cox's Bazar), with which it has divulged the complete extent and comprehensive seasonal variation of the saltwater plume. The abrupt decrease of the resistivity values from 2012 to 2019 conclusively indicate the gradual increment of intensity regarding saline water intrusion throughout the years. In order to assign resistivity ranges to lithology and water quality, the geological and hydrogeological findings have been carefully scrutinized and correlated from literature. Chemical analysis of a few representative groundwater samples reveals trends between resistivity values and existing water chemistry. A three dimensional hydrogeophysical and GIS model of annual saline water intrusion pattern have been prepared in which the rainfall and the anthropogenic water pumping is considered as the driving force controlling the horizontal and lateral fluctuation of the freshwater-salinewater interface. By comparing the models of different time periods, the regional hydrogeological behaviour has been assessed.

The electrical resistivity data has been acquired in both December (pre-monsoon) and June (during monsoon) in the shoreline area of Cox's Bazar, Chittagong, Bangladesh. Since the data was acquired very close to the beach section, the variation in the form of seawater intrusion in the unconfined coastal aquifers of Cox's Bazar has also been evaluated from the perspective of oceanic oscillations such as tides. However, if we negate the effect of tidal variation, the freshwater-seawater interface descends below 10 meters from topographic elevation, in a distance of approximately 200-250 meters inland from the high tide point on the beach. This saltwater intrusion dynamics has been correlated to some of the established climate prediction models to offer a reasonable prediction regarding the intensity of this unlikely scenario in near future.