Preventing Seawater Intrusion and Enhancing Safe Extraction Using Finite‐Length, Impermeable Subsurface Barriers: 3D Analysis

Abstract

Subsurface physical barriers have been recognized as effective in mitigating seawater intrusion in coastal aquifers, although mainly 2D (cross-sectional) barrier effects have been considered. In this study, impermeable barriers with finite shore-parallel lengths are investigated through 3D numerical simulation, thereby extending previous analyses. Two scenarios are considered: (a) barrier-only and (b) barrier-well systems; and three available barrier types are analyzed and compared: (1) subsurface dam, (2) cutoff wall, and (3) fully penetrating barrier. Barrier location, length, and height are investigated, and barrier effectiveness is evaluated from seawater volumes, seawater wedge toe positions, and maximum safe pumping rates. In the barrier-only system, a better performance in preventing seawater intrusion was achieved by cutoff walls rather than subsurface dams. Finite-length subsurface dams may slightly enhance seawater extent along parts of the coastline that are beyond the dam's length. Cutoff walls performed best when located at relatively small distances from the coast in the barrier-only system, whereas with a well at 450 m from the shoreline, the subsurface dam located at a critical distance from the sea (i.e., 300 m in the current study) performed optimally (from the tested cases) and was superior to cutoff walls in terms of the maximum safe pumping rate. A fully penetrating barrier outperformed cutoff walls and subsurface dams, as expected. Our investigation indicates that subsurface barrier design should consider the effect of the shore-parallel length, because barrier benefits may otherwise be significantly overestimated.

Effects of mixed physical barrier on residual saltwater removal and groundwater discharge in coastal aquifers

“…To prevent SWI and protect groundwater resources, researchers have proposed several measures, such as optimizing the layout of pumping wells, artificial recharge, pumping inland saltwater and constructing underground physical barriers (Abarca et al, 2006; Armanuos et al, 2019; Botero‐Acosta & Donado, 2015; Todd, 1974). Compared to other methods, underground physical barriers can not only restrain SWI effectively, but also store fresh groundwater resources (Wu et al, 2020; Yan et al, 2021). In addition, it requires minimal post‐maintenance and is considered to prevent SWI permanently (Allow, 2011; dos Santos Gomes et al, 2018).…”

Impacts of Subsurface Dam Construction on Downstream Groundwater Levels and Salinity in Coastal Aquifers

“…Designs of subsurface dams, including the dam geometry and the selection of dam location, are usually determined based on the required water storage capacity (Imaizumi et al 1988), optimal effectiveness of sea water intrusion control (Luyun et al 2009; Chang et al 2019; Wu et al 2020), and the minimization of accumulations of contaminants in the upstream area (Sun et al 2019). Our model results revealed the impacts of the dam crest elevation and the dam location on groundwater level fluctuations and sea water intrusion in the downstream area.…”

“…However, numerical studies of subsurface dams often adopt a two‐dimensional (2D) model and assume a flat aquifer bottom, which may not always be representative of real world situations. In fact, three‐dimensional (3D) models are necessary to account for the effects of subsurface dams on the radial flow fields and the overall water budget of the aquifer (Kaleris and Ziogas 2013; Wu et al 2020). Especially, groundwater‐storage‐type subsurface dams are designed to effectively raise groundwater levels, for example, by over ten or tens of meters in unconfined aquifers (Japan Green Resources Corporation 2004).…”

Assessing the protective effect of cutoff walls on groundwater pumping against saltwater upconing in coastal aquifers

“…Kaleris and Ziogas (2013) provided a thorough numerical analysis examining the impact of cutoff walls against SWI and groundwater withdrawals. Also, using numerical modelling tools, Wu et al, (2020) provided a comprehensive comparative analysis of the performance of underground barriers in preventing SWI and protecting groundwater abstraction by incorporating the third dimension, thereby extending previous analyses.…”

“…While a number of laboratory and numerical studies have contributed to exploring the performance of cutoff walls against the encroachment of saline water into the aquifer (e.g., Luyun et al, 2011;Abdoulhalik and Ahmed, 2017b), little attention has been given to the assessment of their ability to protect freshwater abstraction wells from salinisation (e.g. Kaleris and Ziogas, 2013;Wu et al, 2020). Shen et al (2020) have recently demonstrated the impact of cutoff walls on groundwater flow and salinity distribution in coastal aquifers under the influence of tidal activity.…”