Identification of seawater intrusion signatures through geochemical evolution of groundwater: a case study based on coastal region of the Mahanadi delta, Bay of Bengal, India

A. K. Behera (), G. J. Chakrapani, S. Kumar and N. Rai
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A. K. Behera: Indian Institute of Technology Roorkee
G. J. Chakrapani: Indian Institute of Technology Roorkee
S. Kumar: National Institute of Hydrology
N. Rai: Indian Institute of Technology Roorkee

Natural Hazards: Journal of the International Society for the Prevention and Mitigation of Natural Hazards, 2019, vol. 97, issue 3, No 13, 1209-1230

Abstract: Abstract The study dealt with seawater intrusion process in a coastal aquifer system in the Mahanadi river delta region in the east coast of India along the Bay of Bengal. The aquifers of Mahanadi delta are characterized as shallow aquifers ( 50 m). Electrical conductivity (EC) of groundwater varied from a fresh of 146 μS/cm (NW of the Mahanadi delta) to a saline of 33,900 μS/cm (close to sea coast) with cation dominance in the order Na+ > Ca2+ > Mg2+ > K+ and anion dominance of Cl− > $$ {\text{HCO}}_{3}^{ - } $$ HCO 3 - > $$ {\text{SO}}_{4}^{2 - } $$ SO 4 2 - . The hydrochemical facies changed from Ca–Mg–Na–HCO3 type to Na–Cl type along the groundwater flow direction due to ion exchange processes. A strong positive correlation (r > 0.9) between Cl− with EC, Na+, Mg2+, Ca2+, $$ {\text{SO}}_{4}^{2 - } $$ SO 4 2 - and K+ was observed, which indicated the influence of seawater on coastal aquifer. The ionic ratios (Na+/Cl−, $$ {\text{HCO}}_{3}^{ - } $$ HCO 3 - /Cl−, Mg2+/Ca2+, $$ {\text{SO}}_{4}^{2 - } $$ SO 4 2 - /Cl−, Ca2+/( $$ {\text{HCO}}_{3}^{ - } $$ HCO 3 - / $$ {\text{SO}}_{4}^{2 - } $$ SO 4 2 - )) also suggested that the groundwater is affected by seawater intrusion. Stable isotope compositions (δ18O and δ2H) varied from − 1.86 to − 6.87 ‰ for δ18O and from − 10.79 to − 45.42 ‰ for δ2H, implying the mixing of saline water and fresh groundwater in the coastal region of the Mahanadi delta. The proportion of seawater in groundwater was estimated to vary from 0% in the upper-delta formation to 72% in the lower-delta formation of the Mahanadi delta (close to seacoast), which was due to inland intrusion of seawater. In a first ever study on this coastal aquifer along the Bay of Bengal, where a large population is dependent on agriculture, seawater intrusion into the fresh groundwater has been quantified. The issue of seawater intrusion into the coastal aquifer in this region may become a serious disaster, if appropriate management strategies are not implemented in time.

Keywords: Seawater intrusion; Stable isotopes; Cation exchange; Mahanadi delta; Coastal aquifer; Bay of Bengal (search for similar items in EconPapers)
Date: 2019
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DOI: 10.1007/s11069-019-03700-6

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