Laboratory-Scale Study on the Effect of Underground Dam and Well on the Salinity Intrusion Interface at Coastal Aquifers

Abstract

This study examines the variations in the interface between saltwater and freshwater in coastal areas through laboratory-scale experiments. The experiments are conducted in a Plexiglas sandbox measuring 1400 mm in length, 200 mm in width, 400 mm in height, and 10 mm in thickness. A semi-uniform sand sample (1-2 mm) is used, and the saltwater, with a concentration of 25 g/L, is tinted with 2 g/L of food dye to facilitate observation of saline water movement in an unconfined coastal aquifer. In the experiments, either a Tabular Well (TW) located at depths of 150 or 250 mm from the soil surface, or an Underground Dam (UGD) with a height of 100, 150, or 200 mm placed on an impermeable layer, is used. The TWs or UGDs are positioned at distances of 250, 500, or 750 mm from the coastline for further analysis. Afterward, the movement of the saltwater interface within the sandbox is monitored using Cartesian coordinates, allowing the determination of flow velocity and its distribution across the soil profile. The results are then analyzed to explore the relationship between the depth and location of either the TW or UGD and the changes in velocity. Observations reveal that the TW reduces the horizontal movement velocity of the saltwater, while the interface velocity exhibits nonlinear variations along the x- and y-axes. Additionally, it is concluded that the well's influence remains consistent over time, whereas the impact of the wall diminishes once the saltwater surpasses the crest.