Analysis of seasonal differences in tidally influenced groundwater discharge processes in sandy tidal flats: A case study of Shilaoren Beach, Qingdao, China

Zhang, Yufeng; Wu, Jingxin; Zhang, Kunkun; Guo, Xinglin; Xing, Cheng; Li, Ning; Wu, Hanfu

doi:10.1016/j.jhydrol.2021.127128

Cited by 13 publications

(8 citation statements)

References 56 publications

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“…Geophysical methods are fast and efficient, and can invert intertidal salinity evolutions by monitoring electromagnetic information (Huizer et al, 2017). In the sandy tidal flat of Shilaoren, Jiaozhou Bay, Zhang Y. et al (2021; and Xing et al (2023) capture the temporal movement of salt-fingering flow via electrical resistivity tomography. Therefore, for SGD field monitoring under the influence of salt-fingering flow, we can use geophysical methods to invert the intertidal salinity distribution, and then accurately capture the width and location of FDZ at the aquifer-sea interface, and finally estimate the temporal and spatial variation of fresh SGD.…”

Section: Discussionmentioning

confidence: 99%

“…Experimental studies of Fang et al (2021Fang et al ( , 2022a and Röper et al (2015) also photographed the flow instability of salt fingers in the intertidal zone via a lab-scale sand tank. In the sandy tidal flat of Shilaoren, Jiaozhou Bay, Zhang Y. et al (2021) and Xing et al (2023) used electrical resistivity tomography and hydrological monitoring to successfully capture the process of unstable USP and subsequent salt-fingering flow. Therefore, the unstable USP associated with salt-fingering flow is a natural phenomenon for some coastal aquifers, which updates the conventional understanding of the salinity distribution in the intertidal zone.…”

Section: Introductionmentioning

confidence: 99%

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Groundwater dynamics in intertidal zones of beach aquifers during salt-fingering flow

Fang,

Qian,

et al. 2023

Front. Mar. Sci.

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At aquifer-sea interfaces, submarine groundwater discharge (SGD) and related chemical loads are closely related to groundwater environment in the intertidal zone of coastal aquifers. Although unstable salinity distribution in the intertidal zone associated with salt-fingering flow has been known as a natural phenomenon for some coastal aquifers, a quantitative understanding of groundwater dynamics in the intertidal zone during salt-fingering flow is still lacking. This study investigated the movement features of salt fingers and the response laws of freshwater discharge zone (FDZ) in the intertidal zone, considering the fixed and seasonal inland conditions. The results revealed that during salt-fingering flow, the finger was repeatedly generated and detached from the intertidal zone. Horizontally, the finger moved toward the sea, and the finger speed first increased at the development stage, then remained unchanged at the separation stage, and finally decreased at the mergence stage. The movement speed of salt fingers was closely related to ambient freshwater flow in the FDZ. In the vertical direction, the finger first permeated downward with a decreasing speed, and then the upward discharge of fresh groundwater in the FDZ region with an increased flow velocity pushed the finger upwards with an increasing speed. In contrast to the results in a stable intertidal regime, the width of FDZ at the aquifer-sea interface fluctuated over time, and the variation trends possessed a well agreement with the flux of fresh groundwater discharge. This suggested that the width of FDZ at the aquifer-sea interface can be used as an indicator of fresh groundwater discharge, even in an unstable regime, to provide a basis for field monitoring. The intensity of salt-fingering flow varied over time under the condition of seasonal freshwater inflow. The mean duration of salt fingers decreased slightly with the increase of seasonal freshwater periods due to a decrease in the interface perturbation for the intertidal environment. These findings lay the foundation for gaining a better understanding of the potential implications of salt-fingering flow on SGD and related solute transports.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Groundwater dynamics in intertidal zones of beach aquifers during salt-fingering flow

Fang,

Qian,

et al. 2023

Front. Mar. Sci.

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“…The depth-of-investigation (DOI) index is used to analyze the influence of inversion parameters on the model and evaluate the reliability of the inverted resistivity data (Oldenburg and Li, 1999;Paepen et al, 2020;Zhang Y. et al, 2021). The DOI index is calculated using Equation 1.…”

Section: Inversion Model Appraisalmentioning

confidence: 99%

“…ERT survey results from different times can provide information about brackish water and seawater intrusion processes that can be analyzed and used to establish different types of coastal seawater-groundwater exchange models (Franco et al, 2009;Misonou et al, 2013;Fu et al, 2020;Zhang, 2021;Zhan et al, 2023;Zhang et al, 2023). Further, the Archie formula, Manning formula, and the salinity box model can be combined to support quantification of the groundwater discharge and salt flux in the tidal flat area Zhang Y. et al, 2021Zhang Y. et al, , 2023Xing et al, 2023).…”

Section: Introductionmentioning

confidence: 99%

The two salinity peaks mode of marine salt supply to coastal underground brine during a single tidal cycle

Xiao,

Zhang,

et al. 2024

Front. Mar. Sci.

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Seawater salt is constantly supplied from the marine environment to coastal underground brine deposits, meaning that brine has the potential for continuous extraction. There is currently a lack of information about the processes that drive the fluxes of seawater salt to underground brine deposits in tidal-driven brine mining areas. We chose the Yangkou salt field on the southern coast of Laizhou Bay, a brine mining area, as our study site. We monitored the spatial and temporal distribution of the underground brine reserve and the changes in water level and salinity in the mining area and adjacent tidal flats using electrical resistivity tomography and hydrogeological measurements. We monitored cross-sections along two survey lines and observed that the underground brine reserve receives a stable supply of seawater salt, and calculated that the rate of influx into the brine body in the mining area near the boundary of the precipitation funnel was 0.226−0.232 t/h. We calculated that a total salt flux of approximately 5.50 t enters the underground brine body every day through a 150 m long shoreline and a 1322.3 m2 window, which is sufficient to sustain the daily extraction of one brine well. During tidal cycles, there are two peaks in the salinity of the water supplied to the underground brine reserve, which means that the brine supply is from at least two high-salinity salt sources in different tidal stages. The first salinity peak occurs during the initial stage of the rising tide after seawater inundates the tidal flat. At this time, seawater, which is a solution and carries a large amount of evaporated salt, is transported into the brine layer through highly permeable areas or biological channels and replenishes the brine in the mining area. The second salinity peak occurs during the early stage of the falling tide. Influenced by hysteresis-driven tidal pumping, high-salinity brine from the lower intertidal zone is rapidly transported into the mining area, thereby increasing the salinity of the underground brine.

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“…Real‐world observations of the USP have been obtained for unconfined coastal aquifers from around the world, including Moreton Island, Australia (Robinson et al., 2006), Waquoit Bay, USA (Abarca et al., 2013), Cape Henlopen, USA (Geng et al., 2017; Heiss & Michael, 2014) and Shilaoren Beach, China (Zhang, Wu, et al., 2021). The USP contains higher velocities than those of the density‐driven saltwater circulation cell (Xin et al., 2010), that is, the saltwater wedge, which is contained in the lower part of the aquifer due to its higher density relative to freshwater.…”

Section: Introductionmentioning

confidence: 99%

Flow and Transport in Coastal Aquifer‐Aquitard Systems: Experimental and Numerical Analysis

Zhang,

Lu,

Shen

et al. 2024

Water Resources Research

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Coastal aquifers are commonly layered, and thus, a clear understanding of groundwater flow and salt transport in layered coastal aquifers is important for managing fresh groundwater. However, the influence of leakage between adjacent aquifers on flow and transport processes remains largely unknown where the influence of tides is considered. This study used laboratory experiments and numerical simulation to examine the processes of flow and transport within a tidal aquifer‐aquitard system (i.e., an unconfined aquifer underlain by a semi‐confined aquifer, with an intervening thin aquitard). The laboratory‐scale observations of the current study are the first observations of offshore fresh groundwater within a semi‐confined coastal aquifer. The numerical and laboratory results are in close agreement, revealing that upward leakage from the semi‐confined aquifer into the saltwater wedge of the overlying unconfined aquifer caused buoyant instabilities to form. The development of freshwater fingers created complex saltwater‐freshwater mixing, leading to mixed saltwater influx‐efflux patterns across the sloping aquifer‐ocean interface. Compared with non‐tidal conditions, tidal forces reduced the net upward leakage from the semi‐confined aquifer to the overlying unconfined aquifer. This increased the horizontal flow toward the sea, which in turn reduced the extent of the saltwater wedge in the semi‐confined aquifer. The higher rates of both fresh and saline submarine groundwater discharge (SGD), caused by tides, led to lower groundwater ages in the semi‐confined aquifer. These findings have important implications for unveiling the complex characteristics of seawater intrusion, SGD and geochemical hotspots within layered coastal aquifers.

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Analysis of seasonal differences in tidally influenced groundwater discharge processes in sandy tidal flats: A case study of Shilaoren Beach, Qingdao, China

Cited by 13 publications

References 56 publications

Groundwater dynamics in intertidal zones of beach aquifers during salt-fingering flow

Groundwater dynamics in intertidal zones of beach aquifers during salt-fingering flow

The two salinity peaks mode of marine salt supply to coastal underground brine during a single tidal cycle

Flow and Transport in Coastal Aquifer‐Aquitard Systems: Experimental and Numerical Analysis

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