Why seawater intrusion has not yet occurred
in the Kaluvelli-Pondicherry basin, Tamil Nadu, India
Received: 13 September 2016 /Accepted: 10 February 2017 /Published online: 17 March 2017
Springer-Verlag Berlin Heidelberg 2017
Abstract Worldwide, coastal aquifers are threatened by sea-
water intrusion. The threat is greatest when aquifers are
overexploited or when recharge is low due to a semi-arid or
arid climate. The Kaluvelli-Pondicherry sedimentary basin in
Tamil Nadu (India) presents both these characteristics.
Groundwater levels in the Vanur aquifer can reach 50 m below
sea level at less than 20 km inland. This groundwater depletion
is due to an exponential increase in extraction for irrigation over
35 years. No seawater intrusion has yet been detected, but a
sulphate-rich mineralization is observed, the result of upward
vertical leakage from the underlying Ramanathapuram aquifer.
To characterize the mechanisms involved, and to facilitate ef-
fective water management, hydrogeological numerical model-
ling of this multi-layered system has been conducted. Existing
and acquired geological and hydrodynamic data have been
applied to a quasi-3D hydrogeological model, NEWSAM.
Recharge had been previously quantified through the inter-
comparison of hydrological models, based on climatological
and surface-flow field measurements. Sensitivity tests on pa-
rameters and boundary conditions associated with the sea were
performed. The resulting water balances for each aquifer led to
hypotheses of (1) an offshore fresh groundwater stock, and (2)
a reversal and increase of the upward leakage from the
Ramanathapuram aquifer, thus corroborating the hypothesis
proposed to explain geochemical results of the previous study,
and denying a seawater intrusion. Palaeo-climate review sup-
ports the existence of favourable hydro-climatological condi-
tions to replenish an offshore groundwater stock of the Vanur
aquifer in the past. The extent of this fresh groundwater stock
was calculated using the Kooi and Groen method.
Keywords Coastal aquifer
In a coastal aquifer, records of decreasing groundwater levels
are a concern both for the overexploitation it reveals, and for
the seawater intrusion which it could, and will probably, in-
duce. If not already detected, the main concern about such a
threat is when it will happen. The threat of seawater intrusion
on coastal overexploited aquifers is a worldwide issue.
Numerous case studies have been published about seawater
intrusion occurring as a result of over-exploitation of aquifers.
For instance, case studies that address similar geological and
hydro-climatological conditions to the area described in this
report include: in a sedimentary basin, Habtemichael and
Fuentes (2016, Florida, USA); in a semi-arid context, Larabi
et al. (1999, Tetouan, Morocco); in an agricultural coastal
plain, Zeng et al. (2016, Laizhou Bay, China); and in India,
Ghassemi et al. (1995), and more particularly in Tamil Nadu,
Jayakumar and Siraz (1997, Cauvery delta), and Ramesh et al.
(1995, Chennai area). When no seawater intrusion is identified
although it is feared, several hypotheses can be formulated
concerning the geological or hydrogeological conditions.
First of all, a stratigraphic shortstop, or a lateral modification
* Aude Vincent
Département d’Hydrogéologie, UMR EMMAH, Université
d’Avignon et des Pays de Vaucluse, Avignon, France
UPMC-Sorbonne Universités, UFR 918, 4 Place Jussieu,
75252 Paris Cedex 05, France
ENS-PSL Research University & CNRS, UMR 8538, Laboratoire de
Géologie, 24 rue Lhomond, 75231 Paris Cedex 05, France
Hydrogeol J (2017) 25:1893–1907