Characteristics of active seawater intrusion

Abstract

The inland migration of seawater in coastal aquifers, known as seawater intrusion (SWI), can be categorised as passive or active, depending on whether the hydraulic gradient slopes downwards towards the sea or the land, respectively. Despite active SWI occurring in many locations, it has received considerably less attention than passive SWI. In this study, active SWI caused by an inland freshwater head decline (FHD) is characterised using numerical modelling of various idealised unconfined coastal aquifer settings. Relationships between key features of active SWI (e.g., interface characteristics and SWI response timescales) and the parameters of the problem (e.g., inland FHD, freshwater-seawater density contrast, dispersivity, hydraulic conductivity, porosity and aquifer thickness) are explored for the first time. Sensitivity analyses show that the SWI response timescales under active SWI situations are influenced by both the initial and final boundary head differences. The interface is found to be steeper under stronger advection (i.e., caused by the inland FHD), higher dispersivity and hydraulic conductivity, and lower aquifer thickness, seawater density and porosity. The interface movement is faster and the mixing zone is wider with larger hydraulic conductivity, seawater-freshwater density difference, and aquifer thickness, and with lower porosity. Dimensionless parameters (Peclet number and mixed convection ratio) from previous steadystate analyses offer only limited application to the controlling factors of passive SWI, and are not applicable to active SWI. The current study of active SWI highlights important functional relationships that improve the general understanding of SWI, which has otherwise been founded primarily on steady-state and passive SWI.

Application of numerical models to assess multi-source saltwater intrusion under natural and pumping conditions in the Great Maputo aquifer, Mozambique

“…These negative impacts can be attributed to an increase in the water consuming activities and uncontrolled and unregulated groundwater abstractions, among others (Shah et al 2000;Ferguson and Gleeson 2012;Alfaro et al 2017). Salinization is largely caused by the dissolution of salt deposits (mainly halite), mixing with trapped seawater or recent seawater intrusion (Barlow and Reichard 2010;Tran et al 2012;Badaruddin et al 2017).…”

Coastal aquifers: Scientific advances in the face of global environmental challenges

“…Parameter combinations are offered to distinguish the transitions from one form to another, and the key characteristics of each type of seawater intrusion (SWI) is described based on the results from numerical simulations. Active seawater intrusion, which arises when the coastal groundwater hydraulic gradient slopes downwards in the inland direction, is the subject of further investigation by Badaruddin et al (2017). They used numerical modelling to provide the first systematic characterization of active seawater intrusion.…”

Status of seawater intrusion in coastal aquifer of Gujarat, India: a review

“…SWI has been defined as the flow of water towards the land from the sea into the adjoining inland aquifer system [4]. Foregoing research and investigations have acknowledged two basic categories of SWI: (i) active and (ii) passive [5][6][7]. In the active SWI, the hydraulic gradients tilt in the direction of the land, and strengths originated by the disparities in densities and crude groundwater movement proceed within the similar direction, initiating additional insistent salinization [7], whereas the hydraulic gradient angles in the direction towards the sea in case of passive SWI.…”

“…Foregoing research and investigations have acknowledged two basic categories of SWI: (i) active and (ii) passive [5][6][7]. In the active SWI, the hydraulic gradients tilt in the direction of the land, and strengths originated by the disparities in densities and crude groundwater movement proceed within the similar direction, initiating additional insistent salinization [7], whereas the hydraulic gradient angles in the direction towards the sea in case of passive SWI. This phenomenon evaluates the density-induced strengths which are operating within the reverse track of the natural movement of groundwater, generating symmetrical and wedge-shaped plumes of seawater which are conventionally analogous with SWI [8].…”