Seawater Intrusion in Extremely Heterogeneous Laboratory-Scale Aquifer: Steady-State Results

Abstract

This work used experimental and numerical methods to investigate seawater intrusion (SWI) in a complex heterogeneous laboratory-scale aquifer. We started the analysis with a homogeneous isotropic aquifer as a reference case, then moved to heterogeneous layered aquifers. The study also investigated block-wise synthetic aquifers with different configurations. The seawater wedge toe length generally decreased under heterogeneous conditions, while the freshwater–saltwater dispersion/mixing zone generally increased when compared to the homogenous case. The saltwater–freshwater interface shows a distinct gradient change across boundaries at differing hydraulic conductivities. This was attributed to streamline refraction, which caused a reduction to the angle of intrusion when transitioning from high to low permeability zones and vice versa. The refraction also affected the mixing zone, where additional spreading was also observed when transitioning from high to low permeability zones and vice versa. When low permeability zones predominated the shoreline at the saline water boundary, this produced a shorter saline wedge in the horizontal direction, but it was more expanded vertically. This study provides insight into the general processes of SWI in heterogeneous aquifers and could be used as a basis for defining conceptual models of real-world systems. It highlights the capabilities of the image analysis to capture small perturbations.

Numerical investigation of mixed physical barriers for saltwater removal in coastal heterogeneous aquifers

“…3 . The first heterogeneous scenario involved the creation of a low hydraulic conductivity layer (K = 0.16 cm/s) in the central portion of the aquifer (Abdoulhalik et al 2020 ; Ahmed et al 2022 ). In contrast, the second heterogeneous scenario was characterized by low hydraulic conductivity layers established in both the upper and lower sections of the aquifer, enabling the assessment of heterogeneous effects in distinct flow conditions.…”

“…To track the position of the toe, measurements were taken every ten minutes until the saltwater wedge reached a steady-state condition, defined as the point when the variation in saltwater penetration length remained less than 1.0 mm for a continuous 30-min period. The location of the toe was determined using the 50% saltwater salinity isoline, specifically at 18,000 mg/L, which is also used to delineate the geometry of the saltwater-freshwater interface (Ahmed et al 2022 ).…”