Transient Investigation of Saltwater Upconing in Laboratory-Scale Coastal Aquifer

Abstract

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.