Combined Effect of Tides and Varying Inland Groundwater Input on Flow and Salinity Distribution in Unconfined Coastal Aquifers

Kuan, Woei Keong; Xin, Pei; Jin, Guangqiu; Robinson, C. E.; Gibbes, Badin; Li, Ling

doi:10.1029/2018wr024492

Cited by 46 publications

(69 citation statements)

References 52 publications

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“…What stands out in Figure 5c and Table 3 is a significant decline in the SGD rate as the freshwater input or tidal amplitude decreased. This finding is consistent with that of Kuan et al (2019). In addition, Figure 5c reveals an increase in the oscillation amplitude of SGD over time and a decrease in its frequency, as the freshwater input decreased or the tidal amplitude increased.…”

Section: Tablesupporting

confidence: 88%

“…Figure 5a reveals an increase in the Q t rate (influx and efflux) with a decreasing freshwater input or increasing tidal amplitude, which was also reported by Kuan et al (2019). Furthermore, we found an obvious, irregular fluctuation of Q t values over time for all the experimental cases.…”

Section: Water Exchange Rate Across the Aquifer-sea Interfacesupporting

confidence: 85%

“…Between the USP and SW is a freshwater discharge “tube” where terrestrial fresh groundwater flows into the sea. The above‐mentioned salinity distribution has been confirmed through numerical simulations, field monitoring, and laboratory experiments (Buquet et al., 2016; Heiss & Michael, 2015; Kuan et al., 2019; Robinson, Li, & Barry, 2007; Yu et al., 2019). The numerical results of Robinson, Li, and Barry (2007) indicated that tidal oscillation drove the SW to recede seaward and caused a wider dispersion zone, compared with nontidal conditions.…”

Section: Introductionmentioning

confidence: 69%

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Influence of Tide‐Induced Unstable Flow on Seawater Intrusion and Submarine Groundwater Discharge

Fang

Zheng

et al. 2021

Water Resources Research

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Groundwater is a valuable source of freshwater in coastal areas. The groundwater flux in coastal aquifers generally occurs in two processes: seawater intrusion (SWI) and submarine groundwater discharge (SGD) (Robinson et al., 2018). SWI, the subsurface movement of seawater into freshwater aquifers, is a natural phenomenon in coastal areas (Werner et al., 2013). The hydraulic head difference caused by the density difference between seawater and freshwater drives the landward movement of seawater, thus forming the configuration of a saltwater wedge (SW) (Glover, 1959;Zhang et al., 2019;Zheng et al., 2020). Above the SW, inland fresh groundwater discharges to the sea. Freshwater mixes with saline water at the interface of the SW due to hydrodynamic dispersion. The salinity gradient in this zone drives the convective circulation inside the SW, that is density-driven circulation (Kohout, 1960). The total efflux (including fresh groundwater and circulating seawater) to the sea is commonly termed SGD. Hydrological behaviors in the two processes are not independent, but interrelated. Previous research has shown that increasing fresh groundwater output in coastal aquifers leads to a seaward shift of the SW. The movement of the SW also affects the density-driven circulation flux (Werner et al., 2013). The salinity of groundwater in aquifers can increase due to SWI, thereby reducing the availability of freshwater in coastal areas. Studies have identified SGD as an important source of freshwater, nutrients, metals, and carbon to the ocean, thus impacting coastal water quality and ecosystems (Moore, 2010;Robinson et al., 2018). Research on the hydrological behaviors in the two processes of coastal aquifers is beneficial for the sustainable management of marine and groundwater resources in coastal areas.Most coastlines worldwide experience tidal oscillations that change groundwater flow and solute transport processes in coastal aquifers (Figure 1). Seawater infiltration into coastal aquifers occurs on the rising tide,

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Section: Tablesupporting

confidence: 88%

Section: Water Exchange Rate Across the Aquifer-sea Interfacesupporting

confidence: 85%

Section: Introductionmentioning

confidence: 69%

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Influence of Tide‐Induced Unstable Flow on Seawater Intrusion and Submarine Groundwater Discharge

Fang

Zheng

et al. 2021

Water Resources Research

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“…Sandbox laboratory setups have been extensively utilized to study the fundamental mechanisms of saltwater intrusion in coastal aquifers (Abdoulhalik et al, 2017; Armanuos et al, 2019; Goswami & Clement, 2007; Konz et al, 2008; Kuan et al, 2012; Liu et al, 2017; Robinson et al, 2016; Stoeckl & Houben, 2012; Takahashi et al, 2018; Zhang et al, 2002). The majority of laboratory studies have recreated SWI in homogeneous synthetic aquifers (Abdelgawad et al, 2018; Abdoulhalik & Ahmed, 2018a, 2018b; Q. Chang et al, 2019; Guo et al, 2019; Kuan et al, 2019; Lee et al, 2019; Levanon et al, 2019; Memari et al, 2020; Na et al, 2019; Noorabadi et al, 2017; Shen et al, 2020; Stoeckl et al, 2019; Yu et al, 2019). Nevertheless, sandbox setups have been successfully employed to study freshwater—saltwater interface in aquifers with structured—sedimentary heterogeneity (Houben et al, 2018), in freshwater lenses, located in heterogeneous island aquifers (Dose et al, 2014; Stoeckl et al, 2015), as well as inside fractured porous media (Etsias et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

The impact of aquifer stratification on saltwater intrusion characteristics. Comprehensive laboratory and numerical study

Etsias

Hamill

Águila

et al. 2021

Hydrological Processes

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Laboratory experiments and numerical simulations were utilized in this study to assess the impact of aquifer stratification on saltwater intrusion. Three homogeneous and six layered aquifers were investigated. Image processing algorithms facilitated the precise calculation of saltwater wedge toe length, width of the mixing zone, and angle of intrusion. It was concluded that the length of intrusion in stratified aquifers is predominantly a function of permeability contrast, total aquifer transmissivity and the number of heterogeneous layers, being positively correlated to all three. When a lower permeability layer overlays or underlays more permeable zones its mixing zone widens, while it becomes thinner for the higher permeability strata. The change in the width of the mixing zone (WMZ) is positively correlated to permeability contrast, while it applies to all strata irrespectively of their relative vertical position in the aquifer. Variations in the applied hydraulic head causes the transient widening of WMZ.These peak WMZ values are larger during saltwater retreat and are negatively correlated to the layer's permeability and distance from the aquifer's bottom. Moreover, steeper angles of intrusion are observed in cases where low permeability layers overlay more permeable strata, and milder ones in the inverse aquifer setups. The presence of a low permeability upper layer results in the confinement of the saltwater wedge in the lower part of the stratified aquifer. This occurs until a critical hydraulic head difference is applied to the system. This hydraulic gradient value was found to be a function of layer width and permeability contrast alike.

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“…While tidal effects on SGD and salinity distributions in subterranean estuaries have been studied extensively, previous studies predominately considered single-frequency (monochromatic) tides (Robinson et al, 2007b;Kuan et al, 2019;Shen et al, 2019;Yu et al, 2019a), bichromatic springneap tides (Robinson et al, 2007a;Abarca et al, 2013;Heiss and Michael, 2014;Buquet et al, 2016), or fitted tidal variations with several primary constituents (Levanon et al, 2016;Geng and Boufadel, 2017;Levanon et al, 2017;Yu et al, 2019b). Coastal aquifer systems are commonly subjected to oceanic tidal fluctuations, which likely contain tens of constituents with different fluctuation frequencies and amplitudes (Pawlowicz et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Effects of Multiconstituent Tides on a Subterranean Estuary With Fixed-Head Inland Boundary

Xin

Shen

et al. 2021

Front. Environ. Sci.

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While tides of multiple constituents are common in coastal areas, their effects on submarine groundwater discharge (SGD) and salinity distributions in unconfined coastal aquifers are rarely examined, with the exception of a recent study that explored such effects on unconfined aquifers with fixed inland freshwater input. For a large proportion of the global coastline, the inland areas of coastal aquifers are topography-limited and controlled by constant heads. Based on numerical simulations, this article examines the variation of SGD and salinity distributions in coastal unconfined aquifers with fixed-head inland boundaries at different distances from the shoreline (i.e., 50, 100, 150, and 200 m). The results showed that the fluctuation intensity of freshwater input was enhanced as the inland aquifer extent decreased, e.g., the range of tide-induced fluctuations in freshwater input increased by around 5 times as the inland aquifer extent decreased from 200 to 50 m. The frequency spectra of the fluctuations of SGD and salinity distributions showed that the coastal aquifer of a shorter inland aquifer extent smoothed out fewer high-frequency tidal constituents but enhanced interaction among different tidal constituents. The interaction among tidal constituents generated new low-frequency signals in the freshwater input and salinity distributions. Regressions based on functional data analysis demonstrated that the inland freshwater input and salinity distributions at any given moment were related to the antecedent (previous) tidal conditions weighted using the probability density function of the Gamma distribution. The influence of the antecedent tidal conditions depended on the inland aquifer extent.

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Combined Effect of Tides and Varying Inland Groundwater Input on Flow and Salinity Distribution in Unconfined Coastal Aquifers

Cited by 46 publications

References 52 publications

Influence of Tide‐Induced Unstable Flow on Seawater Intrusion and Submarine Groundwater Discharge

Influence of Tide‐Induced Unstable Flow on Seawater Intrusion and Submarine Groundwater Discharge

The impact of aquifer stratification on saltwater intrusion characteristics. Comprehensive laboratory and numerical study

Effects of Multiconstituent Tides on a Subterranean Estuary With Fixed-Head Inland Boundary

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