Massive withdrawal of groundwater resources due to population growth and rapid industrialization has led to seawater intrusion into the coastal aquifers across the globe. The problem is an emerging challenge as the coastal areas host ≈40% of the total global population. Impacts of the seawater intrusion on the health of the local community, economic and socio-cultural developments in the coastal areas have led to a wide variety of research being conducted. The objective of the present study is to provide a detailed review of the processes that control the seawater intrusion into the coastal aquifers and the necessary measures to mitigate the same. Various methods of investigation and their applicability are explained. Finally, the status of seawater intrusion in India has been discussed in greater detail.

Seawater intrusion in the coastal aquifers of India - A review

Effect of subsurface dams on saltwater intrusion and fresh groundwater discharge

In order to quantify spatio-temporal changes in the hydrogeochemistry of Swarnamukhi river basin, Andhra Pradesh, India, a total of 239 groundwater samples have been collected for pre- and post-monsoon seasons of 2014 and 2015. The geology of the study area is comprised of granite, granitic gneisses, shales, quartzites, laterites and recent alluvium along the river course. Based on the study of geochemical processes of different seasons, it is found that the occurrence of Na and HCO3 in 2014 shifted toward Ca and HCO3 in 2015 due to cation exchange process. Fe shows the higher concentration value than safe limit due to dissolution of ferruginous minerals and domestic sewage discharges. Bivariate plots of various ions and ratios depict the predominance of silicate weathering over carbonate and evaporite dissolution apart from anthropogenic activities in the enrichment of groundwater constituents. High nitrate concentration was observed in the urbanized regions of the basin followed by intense agricultural areas. Geochemical modeling was carried out using mineral saturation index and thermodynamic stability plots to deduce major weathered products. Most of the groundwater samples in the study area are saturated with carbonate minerals but are undersaturated with silicate minerals. Thermodynamic stability plots suggest the formation of kaolinite secondary mineral and presence of aluminosilicate minerals. Fuzzy calculation is applied to determine the water quality index, which categorizes a majority of the samples as excellent to good category for human use. Factor analysis points toward the mixed source identification of ionic constituents. Saline water mixing index model calculation suggests the effect of salinization in coastal areas due to heavy withdrawal of the fresh groundwater resources for various uses, whereas in the mainland it is due to agricultural runoff and domestic waste water.

Identifying source and evaluation of hydrogeochemical processes in the hard rock aquifer system: geostatistical analysis and geochemical modeling techniques

Intrusion of seawater into the coastal aquifers is a major concern as it affects the quality of groundwater. The objective of this study is to delineate the extent of seawater intrusion in the Indian coast based on previous studies and estimate the area as well as locations of seawater intrusion and submarine groundwater discharge based on the groundwater level of the years 2007 and 2017. Several researchers have reported seawater intrusion in the coastal regions of India by different methods of investigation. These studies indicate that the east coast of India is affected greater than the west coast by seawater intrusion. The maximum extent (about 14 km) of seawater intrusion in India is reported in regions north of Chennai. It is estimated that around 7% of the total coastal area is affected by seawater intrusion, where groundwater is below mean sea level. Around 57% of the coastal area of India has groundwater level in the range from 0 to 10 m msl. Future research needs to focus on the areas where seawater intrusion and submarine groundwater discharge were identified based on this study.

Seawater intrusion and submarine groundwater discharge along the Indian coast

Although Iran’s Ghaen Plain provides saffron to much of the world, no regional groundwater quality (GQ) assessment has yet been undertaken. Given the region’s potential for saltwater intrusion and heavy metal contamination, it is important to assess the GQ and determine its main probable source of pollution (MPSP). Such knowledge would allow for informed mitigation or elimination of the potential adverse health effects of this groundwater through its use as drinking water, or indirectly as a result of the consumption of groundwater-irrigated crops. Total dissolved solids, sodium, and chloride in the water of the majority of 16 wells sampled within the region exceeded World Health Organization and Iranian permissible standards for drinking water. The groundwater proved to only be suitable for irrigating salt tolerant crops under good drainage conditions. Due to the precipitation of calcium carbonate in the water supply facilities, the water from all wells was deemed unsuitable for industrial purposes. Heavy metal pollution and contamination indices showed no groundwater contamination. Analysis of ionic ratios and the application of principal components analysis indicated the MPSP to be saltwater intrusion, with the geology subtending the plain, and to a lesser extent, anthropogenic activities. Reducing groundwater withdrawals, particularly those for agricultural production by using high performance irrigation methods could reduce saltwater intrusion and improve GQ in the Ghaen Plain.

https://www.mdpi.com/1660-4601/15/1/172/pdf

Groundwater Pollution Sources Apportionment in the Ghaen Plain, Iran.

Overuse of groundwater in coastal areas, due to high population and agricultural activity results in seawater intrusion into the coastal aquifer. This paper presents the control measures taken to manage aquifer recharge (MAR) and also to overcome the problem of seawater intrusion into the coastal aquifer along the Kalangi river, Nellore district of Andhra Pradesh, India having connectivity with Pulicat (saltwater) lake estuary. Due to overexploitation of groundwater and less rainfall in past years, adjacent seawater has started intruding in the Kalangi river sub-surface and deteriorating groundwater quality up to 11.6 km from the confluence of the river with Pulicat lake. To prevent this situtation, subsurface dams were constructed in traditional manner using local earth material in three different places across the Kalangi river near Sullurpet town. The water storage capacities calculated after the sub-surface dams’ construction are 1.28 mcft at GK Engineering College, 6.23 mcft at Challamagudi and 3.143 mcft at Holy Cross School sites. The Holy Cross School sub-surface dam is the first full scale dam-cum-check dam constructed to prevent salt water intrusion in the Kalangi river at Sullurpet, Nellore district, Andhra Pradesh. At the Kalangi river estuary portion (at the mouth of sea) a groyne was reconstructed over old groyne site with the introduction of clay bed and wooden sheet piles at down stream. Apart from prevention of sea water entry into Kalangi river sub-surface (during seasons) the groyne top level was raised to prevent mixing of high sea water tides with fresh water and ensuring additional storage of fresh water at upstream side. The reconstructed groyne was serving the purpose of obstructing the surface seawater entry in the Kalangi river and water quality has improved in the river as well as in the wells. After construction of sub-surface dam, as per the Simpson ratio classification, there is substantial improvement of water quality in the SHAR infiltration well situated near the Holy Cross School sub-surface dam.

Managed Aquifer Recharge (MAR) by the Construction of Sub- surface Dams in the Semi-arid Regions: A Case Study of the Kalangi River Basin, Andhra Pradesh

P. Muniratnam

Papers

Managed Aquifer Recharge (MAR) by the Construction of Sub- surface Dams in the Semi-arid Regions: A Case Study of the Kalangi River Basin, Andhra Pradesh