Impact of layered heterogeneity on transient saltwater upconing in coastal aquifers

Abstract

This research investigated the effect of layered heterogeneity on transient saltwater upconing in a laboratory-scale coastal aquifer. The experiments were conducted in a 2Dlaboratory flow tank, and the response of the saltwater wedge to pumping was analysed in a heterogeneous aquifer system, where a low permeability layer was constructed in the middle of the aquifer. The SEAWAT code was used for validation and to perform additional simulations to explore the sensitivity of the critical pumping rate and the critical time to the main parameters characterising the low-permeability layer, which included its permeability, thickness and position. The experimental results showed that the presence of layered heterogeneity noticeably altered the shape and the intrusion length of the upconing wedge without inducing a change in the abstraction rate "triggering" saltwater upconing mechanism compared to the homogeneous case. The numerical results of the layered aquifer provided excellent agreement with the experimental data for both the transient toe length and the shape of the steady-state saltwater wedges. The sensitivity analysis revealed that the critical pumping rate and the critical time was found to decrease considerably with decreasing hydraulic conductivity and thickness of the middle layer, which evidences the higher vulnerability of such layered aquifer systems to the saltwater upconing, in comparison to idealised homogeneous systems. The results nonetheless showed that varying the position of the 2 interlayer induced very little change on the critical pumping rate, but the critical time would tend to decrease as the low permeability layer was moved deeper away from the pumping well, particularly for smaller middle layer thickness.

The impact of aquifer stratification on saltwater intrusion characteristics. Comprehensive laboratory and numerical study

“…Liu et al (2014) and Guo et al (2019) studied SWI in tidally affected stratified aquifers, similarly Dalai et al (2020) quantified the impact of shore slope, while Vithanage et al (2012) investigated aquifer salinization due to a tsunami‐like event. Similarly, Mehdizadeh et al (2014), studied saltwater ‐ freshwater interface on confined aquifers with impermeable strata, Abdoulhalik and Ahmed (2017a, 2017b) evaluated the suitability of various coastal protection techniques in layered hydrological systems, while Abdoulhalik et al (2020), investigated the impact of freshwater abstraction in heterogeneous coastal aquifers.…”

Towards a Correlation between Long-Term Seawater Intrusion Response and Water Level Fluctuations

“…The spatial discretisation and dispersivity values satisfied the grid Peclet number criterion. The molecular diffusion was neglected in this work, following other studies e.g., [9,10,13,20,21]. A constant head was set at the coastal boundary (C = 36.16 g/L), and a variable head was set at the inland freshwater boundary (C = 0 g/L).…”

“…Abdelgawad et al [9] found the critical pumping rate of a well, the rate at which 1% salt concentration reaches the well, was more sensitive to the well location than the well depth. Abdoulhalik et al [10] extended their study by analysing the critical pumping rate in layered heterogeneous coastal aquifers. They evidenced that critical pumping rate significantly decreased with decreasing hydraulic conductivity and thickness of the middle layer of the aquifer.…”

Laboratory and Numerical Study of Saltwater Upconing in Fractured Coastal Aquifers

“…Stoeckl et al [55] utilized laboratory testing to introduce the novel concept of post-pumping saline intrusion, which is the phenomenon of seawater intruding further inland than the location of a well after pumping has ceased. While all these studies assumed homogenous aquifer structures, Abdoulhalik et al [56] performed the only experimental study investigating pumping well salinization in heterogeneous-stratified coastal aquifers. Since the hydrodynamics of fractured porous media vary significantly from those of granular aquifers, the fundamental mechanisms of pumping-induced saline intrusion in fractured aquifers are far from understood.…”