A new physical barrier system for seawater intrusion control

Abstract

The construction of subsurface physical barriers is one of various methods used to control seawater intrusion (SWI) in coastal aquifers. This study proposes the mixed physical barrier (MPB) as a new barrier system for seawater intrusion control, which combines an impermeable cutoff wall and a semi-permeable subsurface dam. The effect of the traditionally-used physical barriers on transient saltwater wedge dynamics was first explored for various hydraulic gradients, and the workability of the MPB was thereafter thoroughly analysed. A newly developed automated image analysis based on light-concentration conversion was used in the experiments, which were completed in a porous media tank. The numerical code SEAWAT was used to assess the consistency of the experimental data and examine the sensitivity of the performance of the barriers to various key parameters. The results show that the MPB induced a visible lifting of the dense saline flux upward towards the outlet by the light freshwater. This saltwater lifting mechanism, observed for the first time, induced significant reduction to the saline water intrusion length. The use of the MPB yielded up to 62% and 42% more reduction of the saltwater intrusion length than the semipermeable dam and the cutoff wall, respectively. The performance achieved by the MPB with a wall depth of 40% of the aquifer thickness was greater than that of a single cutoff wall with a penetration depth of 90% of the aquifer thickness (about 13% extra reduction). This means that the MPB could produce better seawater intrusion reduction than the traditionally used barriers at even lower cost.

Transient investigation of saltwater upconing in laboratory-scale coastal aquifer

“…The experiments were carried out for two bead sizes, namely 1090 µm and 780 µm, to examine the effect of hydraulic conductivity changes on the saltwater upconing process. The hydraulic conductivity of the beads was estimated using in situ measurement within the experimental flow tank (Abdoulhalik et al 2017). Various hydraulic gradients were successively imposed to the system, and the corresponding volumetric freshwater discharge was measured.…”

Transience of seawater intrusion and retreat in response to incremental water‐level variations

“…It is often difficult to derive a clear understanding of the mechanisms affecting SWI directly from field‐based investigation (Werner et al, ). The challenge of measuring and quantifying coastal aquifer hydrodynamics and SWI in field sites has promoted the use of laboratory and numerical modelling tools to gain a valuable insight into SWI response to various geological and/or hydrological stresses, such as (a) change in seaward freshwater discharge resulting from fluctuations at the inland head boundary (Abdoulhalik & Ahmed, ; Abdoulhalik & Ahmed, ; Abdoulhalik, Ahmed, & Hamill, ; Goswami & Clement, ; Lu & Werner, ; Robinson, Ahmed, & Hamill, ; Robinson, Hamill, & Ahmed, ) in head‐controlled systems or from variations of the regional freshwater flux (Chang & Clement, ; Stoeckl & Houben, ; Stoeckl, Houben, & Dose, ) in flux‐controlled systems and (b) SLR (Hussain & Javadi, ; Morgan, Bakker, & Werner, ; Morgan, Stoeckl, Werner, & Post, ).…”

Recharge and Turnover of Groundwater in Coastal Aquifers with Emphasis on Hydrochemistry and Isotopes

“…A similar measure has been taken in the Salalah plain by well recharge of treated waste water along the coast line [14,15]. A new approach, which could be more efficient, is when fresh water recharge into the nonsaline part of the coastal aquifer is combined with pumping of saline water near the shoreline [16].…”