Tide-induced fluctuations of salinity and groundwater level in unconfined aquifers – Field measurements and numerical model

Levanon, Elad; Yechieli, Yoseph; Gvirtzman, Haim; Shalev, Eyal

doi:10.1016/j.jhydrol.2016.12.045

Cited by 75 publications

(46 citation statements)

References 35 publications

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“…Salinity and hydraulic head usually react more quickly in the USP than in the SW. For example, salinity at L2‐1 (Figure b) lags only slightly (∼0 h) behind tidal fluctuation (Figure a) due to the shallow depth of L2‐1 and very little time for seawater to infiltrate to L2‐1, whereas salinity at L3–5 (Figure b) lags ∼12 h behind tidal fluctuation (Figure a) due to its long flow path and deep location. The observations in this study are consistent with previous numerical simulations and field observations (Levanon et al, ; Liu et al, ). As for the variations of radium isotopes at L2‐1 (Figures c–e), they show consistent trends with tidal fluctuation and salinity variation except during the high tide when radium isotopes in the near‐surface area suffer from mixing loss induced by the infiltration of low radium seawater.…”

Section: Discussionsupporting

confidence: 93%

Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (²²⁴Ra, ²²³Ra, and ²²⁸Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone

Liu

Jiao

Liang

et al. 2018

Water Resources Research

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The reactive transport of radium isotopes (224Ra, 223Ra, and 228Ra) in coastal groundwater mixing zones (CGMZs) is sensitive to shifts of redox conditions and geochemical reactions induced by tidal fluctuation. This study presents a spatial distribution and temporal variation of radium isotopes in the CGMZ for the first time. Results show that the activity of radium isotopes in the upper saline plume (USP) is comparatively low due to a short residence time and mixing loss induced by the infiltration of low radium seawater whereas the activity of radium isotopes in the salt wedge (SW) is comparatively high due to a long residence time in the aquifer. The spatial distribution of radium isotopes is determined by the partitioning of radium isotopes, groundwater residence time, and relative ingrowth rates of radium isotopes. In addition, the variation of radium isotopes in the USP lags slightly (∼0 h) whereas the fluctuation of radium isotopes in the SW lags significantly (∼12 h) behind sea level oscillation. Tidal fluctuation affects the partitioning of radium isotopes through controlling seawater infiltration and subsequently influences the dynamics of radium isotopes in the USP. Concurrently, seawater infiltration significantly affects geochemical processes such as the production of nutrients and total alkalinity. Therefore, radium dynamics in the USP have implications for these geochemical processes. The variation of radium isotopes in the USP also has potential implications for transformation of trace metals such as iron and manganese because of the close affinity of radium isotopes to manganese and iron oxides.

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Section: Discussionsupporting

confidence: 93%

Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (²²⁴Ra, ²²³Ra, and ²²⁸Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone

Liu

Jiao

Liang

et al. 2018

Water Resources Research

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“…The hourly changes in groundwater levels and conductivity (salinity) levels caused by the semidiurnal tidal pressure wave were also the most apparent groundwater signal in all collected datasets e.g., (Figures 5, 6 and 8). This dynamic is expected to be a common response on low-lying carbonate atoll islands and confirms previous studies on tide-induced fluctuations of salinity and groundwater level in unconfined aquifers [53].…”

Section: Discussionsupporting

confidence: 89%

Atoll Groundwater Movement and Its Response to Climatic and Sea-Level Fluctuations

Oberle

Swarzenski

Storlazzi

2017

Water

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Groundwater resources of low-lying atoll islands are threatened due to short-term and long-term changes in rainfall, wave climate, and sea level. A better understanding of how these forcings affect the limited groundwater resources was explored on Roi-Namur in the Republic of the Marshall Islands. As part of a 16-month study, a rarely recorded island-overwash event occurred and the island's aquifer's response was measured. The findings suggest that small-scale overwash events cause an increase in salinity of the freshwater lens that returns to pre-overwash conditions within one month. The overwash event is addressed in the context of climate-related local sea-level change, which suggests that overwash events and associated degradations in freshwater resources are likely to increase in severity in the future due to projected rises in sea level. Other forcings, such as severe rainfall events, were shown to have caused a sudden freshening of the aquifer, with salinity levels retuning to pre-rainfall levels within three months. Tidal forcing of the freshwater lens was observed in electrical resistivity profiles, high-resolution conductivity, groundwater-level well measurements and through submarine groundwater discharge calculations. Depth-specific geochemical pore water measurements further assessed and confirmed the distinct boundaries between fresh and saline water masses in the aquifer. The identification of the freshwater lens' saline boundaries is essential for a quantitative evaluation of the aquifers freshwater resources and help understand how these resources may be impacted by climate change and anthropogenic activities.

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“…Levanon et al [19,20] suggested that the tidal effect on the groundwater system comprises two main processes: (1) tidal forcing at the sea floor boundary and (2) attenuation at the groundwater level due to capillary effect. They showed that even though the pressure head wave propagation into the aquifer is relatively fast, the actual movement of the freshwater body, which is reflected by fluctuations of GWL and the salinity in the FSI, is slower since it is controlled by the unsaturated hydraulic conductivity within the capillary fringe.…”

Section: Introductionmentioning

confidence: 99%

The Dynamics of Sea Tide-Induced Fluctuations of Groundwater Level and Freshwater-Saltwater Interface in Coastal Aquifers: Laboratory Experiments and Numerical Modeling

et al. 2019

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Laboratory experiments were conducted in a vertical, two-dimensional, rectangular flow tank, simulating the response of a phreatic coastal aquifer to a sea tide. Imposed sinusoidal fluctuations of the saltwater level at one side of the flow tank caused three types of fluctuations: (a) hydraulic head throughout the aquifer, (b) saturation degree within the capillary fringe, and (c) salt concentration surrounding the freshwater-saltwater interface (FSI), all recorded by head, saturation, and salinity sensors, respectively. Significant time lags were observed both in the saturation degree within the unsaturated zone and in the salinity within the FSI. All measured values, recorded by the three types of sensors, were simulated and reproduced using a numerical model. The calibrated model was used for mapping the time lags throughout the aquifer. It was found that the time lag of saturation fluctuations within the unsaturated zone increased upward from the groundwater level as the unsaturated hydraulic conductivity decreased. Similarly, the time lag of salinity fluctuations within the FSI increased downward, with distance from the groundwater level. We interpret the low hydraulic conductivity at the capillary zone as the source of attenuation of both saturation and salinity, because both are controlled by the vertical advection of the whole freshwater body. This advection is significantly slower compared to the dynamics of pressure diffusion. The uniqueness of this study is that it provides quantitative data on the attenuation at the capillary zone and its effect on the salinity time lag in coastal aquifer systems.

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Tide-induced fluctuations of salinity and groundwater level in unconfined aquifers – Field measurements and numerical model

Cited by 75 publications

References 35 publications

Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (²²⁴Ra, ²²³Ra, and ²²⁸Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone

Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (²²⁴Ra, ²²³Ra, and ²²⁸Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone

Atoll Groundwater Movement and Its Response to Climatic and Sea-Level Fluctuations

The Dynamics of Sea Tide-Induced Fluctuations of Groundwater Level and Freshwater-Saltwater Interface in Coastal Aquifers: Laboratory Experiments and Numerical Modeling

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Tide-induced fluctuations of salinity and groundwater level in unconfined aquifers – Field measurements and numerical model

Cited by 75 publications

References 35 publications

Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (224Ra, 223Ra, and 228Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone

Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (224Ra, 223Ra, and 228Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone

Atoll Groundwater Movement and Its Response to Climatic and Sea-Level Fluctuations

The Dynamics of Sea Tide-Induced Fluctuations of Groundwater Level and Freshwater-Saltwater Interface in Coastal Aquifers: Laboratory Experiments and Numerical Modeling

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Product

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Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (²²⁴Ra, ²²³Ra, and ²²⁸Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone

Using Tidal Fluctuation‐Induced Dynamics of Radium Isotopes (²²⁴Ra, ²²³Ra, and ²²⁸Ra) to Trace the Hydrodynamics and Geochemical Reactions in a Coastal Groundwater Mixing Zone