Association of geomorphic features with groundwater quality and freshwater availability in coastal regions

Abstract

Seawater intrusion into coastal aquifers is a global problem as it limits the freshwater availability in coastal regions. A study has been conducted with the aims to identify the processes controlling seawater/freshwater distribution and demarcate potential freshwater zones in an aquifer along the coast of Bay of Bengal. Sixty-eight groundwater samples were collected from 900 sq. km spread along the coast and were analyzed for various physicochemical parameters. Most of the samples show brackish to saline characteristics. The anionic ratio indicates that 65% of groundwater samples are slightly to moderately affected by seawater, while 25% are severely affected. Seawater–freshwater mixing and freshening have been identified as the dominant processes in controlling the groundwater chemistry. Seawater has been traced in 88% of collected samples, and it is found that only 1% mixing of the seawater makes the groundwater unsuitable for drinking purposes. The fraction of seawater in individual samples has been calculated using chloride as a tracer. Thematic maps of seawater tracers have indicated that groundwater with higher salinity is located in the inland areas, whereas patches of fresh groundwater are found near the coast. With the help of satellite imageries, it has been found that the freshwater patches are typically located on paleochannels and sand dunes, which act as local reservoirs to retain freshwater in the seawater affected region. Such geomorphic features are common in coastal environments. Their identification and subsequent utilization as freshwater sources can be of vital importance to deal with freshwater scarcity in the coastal regions across the globe.