Effects of Temperature on Tidally Influenced Coastal Unconfined Aquifers

Nguyen, Thi Minh Thuy; Yu, Xiayang; Li, Pu; Xin, Pei; Zhang, Chenming; Barry, David Andrew; Li, Ling

doi:10.1029/2019wr026660

Cited by 35 publications

(30 citation statements)

References 44 publications

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“…The salt‐freshwater interfaces determined by the simulated 50% isohaline were close to the experimental results, although a slight difference in the SW toe positions between the experimental and simulated results. As previous studies suggested, the food dye during the experiments failed to capture the extension of the dispersion zone (Abdoulhalik & Ahmed, 2018; Nguyen et al., 2020), due to the lack of high resolution image to concentration conversion (Robinson et al., 2016). In addition, discharge of fresh groundwater into the saltwater chamber could reduce the saltwater concentration.…”

Section: Resultsmentioning

confidence: 98%

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: Resultsmentioning

confidence: 98%

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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“…We conducted laboratory experiments under well-controlled conditions ( Figure 2). The experimental apparatus was similar to the tidally influenced unconfined aquifer considered by Nguyen et al (2020). The experimental confined aquifer consisted of a three-compartment heat-insolating flume (2.2 m long, 1.0 m high, and 0.1 m thick).…”

Section: Laboratory Experimentsmentioning

confidence: 99%

“…The groundwater temperature was predicted to range from the frozen temperature (0°C) to 40°C along the global coastline based on Benz et al (2017) (supporting information Figure S1). Coastal seawater temperatures vary seasonally (supporting information Figures S2–S4), and the annually averaged values commonly differ from those for the adjacent groundwater with a range from −15°C (colder seawater) to 15°C (warmer seawater) along the global coastline; for example, for 62.25% of the global coastline seawater is warmer than groundwater by 0°C to 5°C (supporting information Figures S5 and S6) (Locarnini et al, 2013; Nguyen et al, 2020). In the Floridan aquifer, a temperature contrast between groundwater and seawater of up to 40°C was measured (Hughes et al, 2007; Kohout, 1965).…”

Section: Introductionmentioning

confidence: 99%

“…Even so, studies considering the thermal influence are sparse (Bredehoeft & Papaopulos, 1965; Holzbecher et al, 2009; Paldor et al, 2020; Wilson, 2005). Recently, Nguyen et al (2020) examined effects of temperature on tidally influenced coastal unconfined aquifers. They found that temperature can significantly moderate the seawater circulation and salinity distributions in unconfined aquifers.…”

Section: Introductionmentioning

confidence: 99%

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Thermal Effects on Flow and Salinity Distributions in Coastal Confined Aquifers

Xin

Nguyen

et al. 2020

Water Resources Research

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Coastal aquifers provide an important hydrologic connection between terrestrial freshwater and oceanic seawater. Understanding the water flow and salinity distributions in those aquifers is essential to manage seawater intrusion and regional groundwater resources. For the last 50 yr, these processes have been extensively examined; however, previous studies typically assumed isothermal conditions and overlooked groundwater-seawater temperature contrasts, as commonly found along the global coastline. Here, we validated a solute and heat transport model against laboratory experiments and then revisited the classical Henry problem for coastal confined aquifers. We found that as the seawater temperature increases or freshwater temperature decreases, the freshwater-seawater interface retreats seaward and thus the freshwater storage increases. This occurs as a result of temperature-induced changes to the fluid density and aquifer hydraulic conductivity. Furthermore, double diffusion of salt and heat can induce two circulation cells in opposing directions in the saltwater wedge once the seawater temperature exceeds that of groundwater by a certain extent. Consequently, the circulating seawater flux and associated travel time change dramatically compared with isotheral conditions. Overall, the effect of thermal forcing can be significant, as demonstrated by a sensitivity analysis considering a large range of groundwaterseawater temperature contrasts. These results highlight the impact of changing thermal regimes on the flow and salinity distributions in coastal confined aquifers and provide guidance for better assessment of water resources in coastal zones. Plain Language Summary Coastal zones are often densely populated with associated significant economic activity. Groundwater in coastal aquifers provides an essential freshwater resource for domestic and industrial use as well as food production. Intensive human activities and climate change cause water regime shifts and thus threaten water security in coastal areas. Coastal water resource assessments often overlook groundwater-seawater temperature contrasts, even though such contrasts are globally ubiquitous. Here, we show those assessments could be improved with thermal effects considered as temperature contrasts can markedly influence salinity distributions and water circulations in coastal aquifers. The results provide guidance for better assessment of water resources in coastal zones. Water temperature affects oceanland exchange and various biogeochemical processes, which should be considered in future studies including climate change evaluations.

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“…Chapter 4 of this thesis has reported the responses of tidally influenced unconfined aquifers to constant aquifer-ocean temperature contrasts. It was found that the USP expands while the lower saltwater wedge retreats seaward when seawater is warmer than groundwater [Nguyen et al, 2020]. The higher seawater temperature also enhances the aquifer-ocean mass exchange, especially the tidally-induced seawater circulation within the USP, resulting in increased submarine groundwater discharge.…”

Section: Effects In a Tidally Influenced Systemmentioning

confidence: 99%

Seawater intrusion in coastal aquifers: Combined effects of salinity and temperature

Nguyen¹

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Seawater intrusion occurs commonly in coastal aquifers around the world, threatening the availability and usability of fresh groundwater resources for vegetation and human uses. The rapid growth of the world population and urbanization requires sound strategies for protection and management of the freshwater resources, especially coastal groundwater. This goal can only be achieved through proper understanding of the processes that underlie seawater intrusion in coastal aquifers. Major insights have been gained over the past several decades, in particular, roles of the density-driven flow in driving and maintaining the invasive flow of saltwater. However, most studies have linked the seawater intrusion process merely to the level of salt content through the free convection induced by the salinity contrast between groundwater and seawater but ignored their temperature difference. In reality, the thermal contrast between coastal groundwater and marine seawater may range up to 15°C in absolute value with either warmer or colder seawater. Such thermal contrast can alter seawater circulation through the coastal aquifer, which in turn affects the biogeochemical reactions of land-sourced pollutants in the aquifer prior to discharge to the marine ecosystem. This research aimed to investigate the combined effects of salinity and temperature contrasts on the interactions between freshwater and seawater in unconfined coastal aquifers. Using laboratory VII Financial support No financial support was provided to fund this research.

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Effects of Temperature on Tidally Influenced Coastal Unconfined Aquifers

Cited by 35 publications

References 44 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

Thermal Effects on Flow and Salinity Distributions in Coastal Confined Aquifers

Seawater intrusion in coastal aquifers: Combined effects of salinity and temperature

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