Evaporation-Driven Density Instabilities in Saturated Porous Media

Abstract

Soil salinization is a major cause of soil degradation and hampers plant growth. For soils saturated with saline water, the evaporation of water induces accumulation of salt near the top of the soil. The remaining liquid gets an increasingly larger density due to the accumulation of salt, giving a gravitationally unstable situation, where instabilities in the form of fingers can form. These fingers can, hence, lead to a net downward transport of salt. We here investigate the appearance of these fingers through a linear stability analysis and through numerical simulations. The linear stability analysis gives criteria for onset of instabilities for a large range of parameters. Simulations using a set of parameters give information also about the development of the fingers after onset. With this knowledge, we can predict whether and when the instabilities occur, and their effect on the salt concentration development near the top boundary.

Instability Problems and Density-Driven Convection in Saturated Porous Media Linking to Hydrogeology: A Review

“…Instabilities of saline water saturating a porous medium when water evaporates from this medium are under study also in [132] but using two approaches: a linear stability analysis and numerical simulations. Salt accumulated near the evaporation surface is allowed to precipitate.…”

“…The results in [41,[130][131][132] correspond with an approach of semi-infinite domain, that is the lower boundary of the domain is assumed to be far away from the upper boundary and does not influence the dynamic process under study. In this case, the onset of convection is determined by the actual Rayleigh-Darcy number, R c , not including the height of domain.…”

“…As for an influence of initial perturbations on the convection onset in numerical simulations, we found that this issue in the case of imposed throughflow is studied only in [132] where initial perturbations for the salt mole fraction are introduced. In this work, the numerical time of onset of instabilities is defined, and the influence of different initial perturbations is shown.…”

Processes Controlling Formation of Salt Efflorescence in Coastal Salt Flats

“…This phenomenon has been observed in salt lakes (induced by evaporation of surface or ground water in the lakes) (Lasser et al., 2021, 2023; Wooding, Tyler, & White, 1997; Wooding, Tyler, White, & Anderson, 1997), coastal aquifers (due to seawater intrusion) (Van Dam et al., 2009), tidal wetlands (due to dissolution of surface precipitated salts during tidal inundation) (Geng & Boufadel, 2015a; Shen et al., 2018; Stevens et al., 2009; Xiao et al., 2019; Xin et al., 2017; J. Zhang et al., 2021), and agricultural lands (caused by irrigation) (Jambhekar et al., 2015). Such salinity‐driven convection process has attracted wide attention, with most studies focusing on the formation mechanism of density‐driven flow under saturated conditions (Bringedal et al., 2022; Simmons et al., 2001; Slim, 2014; Weatherill et al., 2004; Wooding, Tyler, & White, 1997; Wooding, Tyler, White, & Anderson, 1997). In these studies, the denser water was either introduced directly to the water‐saturated surface or produced by dissolving salt precipitated on the surface.…”

“…Zhang et al, 2021), and agricultural lands (caused by irrigation) (Jambhekar et al, 2015). Such salinity-driven convection process has attracted wide attention, with most studies focusing on the formation mechanism of density-driven flow under saturated conditions (Bringedal et al, 2022;Simmons et al, 2001;Slim, 2014;Weatherill et al, 2004;Wooding, Tyler, White, & Anderson, 1997). In these studies, the denser water was either introduced directly to the water-saturated surface or produced by dissolving salt precipitated on the surface.…”