Influence of the subsurface physical barrier on nitrate contamination and seawater intrusion in an unconfined aquifer

Ke, Shengnan; Chen, Jiajun; Zheng, Xilai

doi:10.1016/j.envpol.2021.117528

Cited by 22 publications

(6 citation statements)

References 49 publications

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“…This is mainly because the studied aquifer was a flux‐controlled system (i.e., groundwater discharge was controlled by rainfall recharge), which kept the total freshwater discharges to the sea before t dam and after t full very similar (assuming no significant groundwater abstractions after t full ). However, in the case of a head‐controlled system (i.e., groundwater discharge is controlled by large surface water bodies), subsurface dams would lower the hydraulic gradients in the upstream area and permanently decrease groundwater discharge to the sea (Chang et al 2019; Sun et al 2019; Ke et al 2021). Under such situations, subsurface dam construction would cause irreversible sea water intrusion.…”

Section: Resultsmentioning

confidence: 99%

“…Several laboratory and numerical experiments have demonstrated that a subsurface dam should be designed to be higher than a critical height at a specified position to achieve effective control of sea water intrusion (Luyun et al 2009; Chang et al 2019; Zheng et al 2021). However, a higher dam height would not only increase the construction cost, but also reduce fresh groundwater discharge in a head‐controlled aquifer, which favors the accumulation of land‐based pollutants in the subsurface reservoir (Chang et al 2019; Sun et al 2019; Ke et al 2021). These studies contribute valuable insights with respect to improving the environmental performance of subsurface dams.…”

Section: Introductionmentioning

confidence: 99%

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

2023

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Subsurface dam is a promising engineering technology for groundwater resources development. However, the possible impacts of these dams on the groundwater environment have been a major concern. Here, we used a three‐dimensional (3D), variable‐density, unsaturated‐saturated groundwater flow model to explore how a groundwater‐storage‐type subsurface dam, built in the freshwater domain of an unconfined coastal aquifer, affected groundwater levels and salinity in the downstream area. Model results suggested that, after subsurface dam construction, groundwater levels in the downstream area showed intensified fluctuations in terms of phase advances, greater amplitudes, and higher frequencies following heavy rainfall events. Numerical simulations with variable subsurface dam scenarios indicated that the groundwater level fluctuations were further intensified with a higher crest elevation or a shorter distance from the coast. Moreover, during the recharging period of the subsurface reservoir, sea water in the downstream area intruded landward from its initial location, which can at least temporarily threaten water quality near the coast. A higher dam crest elevation prolonged the duration of sea water intrusion, while a dam positioned closer to the coast induced sea water intrusion with a greater horizontal extent. General implications are discussed with respect to improving assessment methodologies and engineering designs of subsurface dams.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2023

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“…The aforementioned studies primarily concentrate on natural aquifers, overlooking the aquifers influenced by human activities. Numerous coastal regions have constructed subsurface dams within aquifers to counteract seawater intrusion and safeguard subsurface freshwater resources (Chang et al, 2019;Ke et al, 2021;Sun et al, 2021). Subsurface dams are constructed through the injection of virtually impermeable materials into the aquifers (Abdoulhalik and Ahmed, 2017).…”

Section: Introductionmentioning

confidence: 99%

Variable-density solute transport in unconfined coastal aquifers with a subsurface dam

Fan,

Shen,

Xie

et al. 2024

Front. Mar. Sci.

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Recently, the influence of subsurface dams on solute transport in coastal aquifers has become a hot research topic. Although many studies have been conducted, the combined effects of subsurface dam and tides on variable-density solute transport remain unclear, and this study aimed to fill this research gap. In the current study, a numerical model representing a 2-D cross-shore coastal aquifer was established. The model simulated cases with and without a subsurface dam, and sensitivity analysis cases with different height and location of the subsurface dam and solute concentration. The results show that a subsurface dam blocks a portion of the solute plume, which can only be discharged by dilution at the edges, thereby altering its discharge pattern and reducing their discharge rate. The addition of a subsurface dam may either prolong or shorten the residence time of solute,depending on the location rather than the height of the subsurface dam. In particular, a more landward subsurface dam would significantly increase the residence time; sensitivity analysis demonstrates that both the landward shift and the height increase of the subsurface dam contribute to a heightened ratio of dynamic mass distribution for the solute plume within the freshwater and saltwater zones of the aquifer, with maximum changes in mass distribution ratios of 87.22% and 300%, respectively. Also, these factors cause the solute to migrate both seaward and landward, respectively, across the primary outflow regions of the aquifer-ocean interface. Results from this study may provide theoretical guidance for the optimal design and environmental impact assessment of subsurface dams.

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“…Currently, several methods, such as the artificial recharge of groundwater or the establishment of subsurface dams, have been proposed to address the issue of seawater intrusion [12][13][14][15][16][17][18][19][20][21][22][23]. Onder et al [24] detailed the types, design, and construction techniques of subsurface dams and suggested dams as a means of sustainable development.…”

Section: Introductionmentioning

confidence: 99%

Study on the Control of Saltwater Intrusion Using Subsurface Dams

Chang,

Chen,

Liu

et al. 2023

Water

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Subsurface dams are widely used to prevent saltwater intrusion, with good results. This blockage often leads to an accumulation of pollutants and salt on the inland and seaside of the dam, respectively. While the latter is intended, the former effect is not desired and poses a huge problem in groundwater management. In order to quantitatively address this issue and clarify the impact of subsurface dam height, location, and the head difference for the saltwater and freshwater boundary on saltwater wedges and fresh groundwater discharge, a flow tank and numerical model were constructed. The results indicate that there was an optimal effective dam height and location (also the minimum effective dam location) for controlling saltwater intrusion, which corresponded to the maximum groundwater and freshwater discharge. When the various conditions of the numerical model were set according to the flow tank and the dam was 15 cm away from the saltwater boundary, the minimum effective dam height was equal to the aquifer thickness multiplied by 0.36. The dam height reached a height that was slightly higher than the minimum effective height, namely, the ratio of dam height to aquifer thickness was 0.38, which revealed that the freshwater discharge reached its maximum at 22.71 cm3/min, the saline water wedge area was the smallest at 378 cm2, and the prevention effect of saltwater intrusion was the best. Building a dam too high, that was, the ratio of dam height to aquifer thickness exceeded 0.38, resulted in an increased saltwater wedge area and exacerbated aquifer pollution. When the dam was located at the minimum effective distance for preventing saltwater intrusion under a certain dam height and head difference between saltwater and freshwater boundary, that was, the ratio of the distance of the dam to the saltwater boundary to the total length of the aquifer was 0.063, the distance of the dam to the saltwater boundary was the minimum effective distance. Compared to other effective distances, when the dam was at the minimum effective distance, the freshwater discharge reached its maximum at 22.71 cm3/min, and the saltwater wedge area was the smallest at 378 cm2. These conclusions provide a theoretical reference for the impact of subsurface dam construction on the saltwater wedge. This study examines the impact of tides and waves on the water head of the saltwater boundary, and it is also necessary to verify these conclusions through actual field experiments. We will investigate this in future work.

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Influence of the subsurface physical barrier on nitrate contamination and seawater intrusion in an unconfined aquifer

Cited by 22 publications

References 49 publications

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

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

Variable-density solute transport in unconfined coastal aquifers with a subsurface dam

Study on the Control of Saltwater Intrusion Using Subsurface Dams

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