Laboratory and Numerical Study of Saltwater Upconing in Fractured Coastal Aquifers

Georgios Etsias,Jesús F Águila,Samuel Kennerley,Ashraf A Ahmed,Christopher Thomson,Gerard A Hamill,Raymond Flynn,Mark C Mcdonnell,Eric M Benner

doi:10.3390/w13233331

Abstract

This study investigated the saltwater upconing mechanism in fractured coastal aquifers. Head-induced saline intrusion was initiated into three narrow sandbox aquifers containing individual horizontal discontinuities placed on different positions. Subsequently, using a peristaltic pump, freshwater was abstracted from the aquifers’ center, triggering saltwater upconing. Progressively larger pumping rates were applied until critical conditions, resulting in the wells’ salinization, were achieved. Advanced image analysis algorithms were utilized to recreate the saltwater concentration fields and quantify the extent of the saline wedges with a high accuracy. A numerical model was successfully employed to simulate the laboratory results and conduct a comprehensive sensitivity analysis, further expanding the findings of this investigation. The impact of the fractures’ length, permeability and position on the upconing mechanism was identified. It was established that the presence of high permeability discontinuities significantly affected aquifer hydrodynamics. The conclusions of this study could constitute a contribution towards the successful management of real-world fractured coastal aquifers.

Highlights

Accepted: 22 November 2021Freshwater overexploitation is the main cause of saltwater intrusion (SWI) in coastal aquifers across the globe [1,2,3]
Since mixing freshwater with only 1 percent of seawater makes it unfit for drinking [5], pumpinginduced saline intrusion could potentially threaten the access to freshwater for one half of the global population which currently resides less than 200 km from the coast [6]
Since for the fractured-left aquifer, the saltwater–freshwater interface generated by an abstraction rate of 0.8 ml/sec included a higher salinity concentration zone protruding towards the pumping well, the measured salinity of this case was included in Table 2 to assure that no critical abstraction was reached during that stage

Summary

Introduction

Accepted: 22 November 2021Freshwater overexploitation is the main cause of saltwater intrusion (SWI) in coastal aquifers across the globe [1,2,3]. When excessive freshwater is abstracted from coastal hydrological systems, the saltwater–freshwater interface may move further landward, reaching the location of the pumping wells. This physical mechanism, called saltwater upconing [4], can lead to the eventual salinization of abstraction wells. Coastal fractured aquifers are generally more vulnerable to saltwater intrusion than other hydrological systems [13]. This vulnerability was the driving force behind multiple studies, utilizing both field scale experimental observations [14,15,16,17,18]

Methods

Results

Conclusion