Abstract:
Seawater intrusion is the influx of saline water into freshwater aquifers leading to
groundwater quality degradation. The Kalpitiya Coastal Aquifer (KCA) of Sri
Lankan is a limestone aquifer and its’ adjacent groundwater is influenced by saline
water. However, saltwater intrusion modeling has not been deeply investigated
in coastal regions in the Sri Lankan context. Hence, this study aims to provide
significant information to protect the KCA from contamination by seawater
intrusion. A 3D variable-density groundwater flow model was used in this study
to evaluate how far inland seawater has moved in the present and future situations.
The model input parameters were chosen after reviewing geological records and
permeability tests obtained from the National Water Resources Board, Sri Lanka.
The numerical model for the pair density-dependent flow system was solved using
the SEAWAT code. The estimated model was then run for the following 20 years
(2016-2036) with the same hydrological parameters to assess the magnitude of
seawater intrusion under four different scenarios (Scenario 1: no-change occurs in
the model; Scenario 2: pumping from the aquifer increase by doubling in the same
pumping wells; Scenario 3: three new agricultural wells will be opened within the
second scenario; Scenario 4: change in the annual precipitation rate occurs (20%
reduction of annual precipitation). Scenario 3 demonstrated that water pumping
from agricultural wells may lead to reduce or reverse groundwater gradient.
Overall, the modeled results depicted that the aquifer beneath the KCA is
susceptible to increased groundwater pumpage. Therefore, the aquifer should be
continuously monitored to determine the progress of seawater intrusion and
suggest the best solutions to prevent the intrusion. As new data becomes available,
the model should be modified to reduce the uncertainty in the simulations.
