The objective of this research was to examine the response of seawater intrusion and
retreat to freshwater abstraction from a well in laboratory-scale coastal aquifer under transient
conditions. This has been done experimentally and numerically through qualitative and
quantitative analysis. The laboratory experiments were completed in a two-dimensional
laboratory tank for two beads sizes, namely 1090 µm and 780 µm. The SEAWAT code was
used for the numerical simulations. The experimental results showed that the vulnerability of
the pumping well to salinization was higher for the low permeability aquifer, whereby the
saltwater upconing process was observed at an abstraction rate 40 % smaller in the lower
permeability aquifer compared to the high permeability aquifer. In the lower permeability
scenario, the inland penetration of the saline plume was up to 41% larger than in the higher
permeability scenario, for an equivalent pumping rate increment. In addition, the process of
decay (after the abstraction had ceased) of the wedge was slower in the lower permeability
aquifer, which suggests a slower retreat of the wedge. The qualitative comparison of the shape
of the saline plume and the quantitative comparison of the transient toe length data between
experimental and numerical results showed excellent agreement. The flow velocity field
analysis revealed that the local reduction of the magnitude of the flow velocity along the upper
part of the interface was a major factor contributing to the saltwater upconing mechanism
