Effects of alongshore morphology on groundwater flow and solute transport in a nearshore aquifer

Zhang, Ying; Li, Ling; Erler, Dirk V.; Santos, Isaac R.; Lockington, David

doi:10.1002/2015wr017420

Cited by 33 publications

(28 citation statements)

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“…Heterogeneous aquifer properties should be investigated. Three‐dimensionality linked strongly to the beach morphology and land surface topography is likely to alter the SGD and SWI [ Zhang et al ., ]. Local topographic variations, rather than the idealized geometry used here, are expected to affect rainfall infiltration and groundwater flow in both cross‐shore and along‐shore directions. Wave forcing and multiple tidal constituents (e.g., combined semidiurnal solar and lunar tides) were not considered.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

“…Most coastlines worldwide are exposed to tides. The effect of tides on subterranean estuaries has been studied intensively over the last 10 years [Anschutz et al, 2009;Heiss and Michael, 2014;Kuan et al, 2012;Li et al, 2008;Mao et al, 2006;Robinson et al, 2006Robinson et al, , 2007aRobinson et al, , 2007bRobinson et al, , 2009Wilson et al, 2015;Zhang et al, 2016]. Tidal fluctuations drive seawater circulations in shallow intertidal aquifers, alter the salt distribution and, under certain conditions, lead to the formation of an upper saline plume (USP) (Figure 1) [Evans and Wilson, 2016;Heiss and Michael, 2014;Robinson et al, 2006Robinson et al, , 2007a.…”

Section: Introductionmentioning

confidence: 99%

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Effects of episodic rainfall on a subterranean estuary

Xin

et al. 2017

Water Resources Research

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Numerical simulations were conducted to examine the effect of episodic rainfall on nearshore groundwater dynamics in a tidally influenced unconfined coastal aquifer, with a focus on both long‐term (yearly) and short‐term (daily) behavior of submarine groundwater discharge (SGD) and seawater intrusion (SWI). The results showed nonlinear interactions among the processes driven by rainfall, tides, and density gradients. Rainfall‐induced infiltration increased the yearly averaged fresh groundwater discharge to the ocean but reduced the extents of the saltwater wedge and upper saline plume as well as the total rate of seawater circulation through both zones. Overall, the net effect of the interactions led to an increase of the SGD. The nearshore groundwater responded to individual rainfall events in a delayed and cumulative fashion, as evident in the variations of daily averaged SGD and salt stored in the saltwater wedge (quantifying the extent of SWI). A generalized linear model (GLM) along with a Gamma distribution function was developed to describe the delayed and prolonged effect of rainfall events on short‐term groundwater behavior. This model validated with results of daily averaged SGD and SWI from the simulations of groundwater and solute transport using independent rainfall data sets, performed well in predicting the behavior of the nearshore groundwater system under the combined influence of episodic rainfall, tides, and density gradients. The findings and developed GLM form a basis for evaluating and predicting SGD, SWI, and associated mass fluxes from unconfined coastal aquifers under natural conditions, including episodic rainfall.

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Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of episodic rainfall on a subterranean estuary

Xin

et al. 2017

Water Resources Research

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“…While this simplification is valuable for developing process-based understanding of the physical and biogeochemical processes in CUAs, there is a need to expand investigations to consider the heterogeneous nature of the system. As illustrated by Zhang et al [2016] and Russoniello et al [2013], alongshore variability and aquifer heterogeneities may play a key role in controlling SGD and the physical and biogeochemical processes in a STE. Further, most studies assume that the beach morphology (cross-shore and alongshore) is constant, neglecting erosional and accretionary beach processes.…”

Section: Knowledge Gaps and Research Needsmentioning

confidence: 99%

“…Alongshore variations associated with, for instance tidal creeks, headlands and embayments and geological heterogeneities are common, but the three-dimensionality of the nearshore groundwater system is not well understood. Zhang et al [2016] showed complex three-dimensional flows and salt transport in a CUA at a field site located adjacent to a tidal creek with strong alongshore morphology variations. Russoniello et al [2013] illustrated the importance of small-scale submarine geological heterogeneities in controlling SGD and salt transport patterns.…”

Section: Tidesmentioning

confidence: 99%

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

Robinson¹,

Xin²,

Santos³

et al. 2018

Advances in Water Resources

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215

148

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Sustainable coastal resource management requires sound understanding of interactions between coastal unconfined aquifers and the ocean as these interactions influence the flux of chemicals to the coastal ocean and the availability of fresh groundwater resources. The importance of submarine groundwater discharge in delivering chemical fluxes to the coastal ocean and the critical role of the subterranean estuary (STE) in regulating these fluxes is well recognized. STEs are complex and dynamic systems exposed to various physical, hydrological, geological, and chemical conditions that act on disparate spatial and temporal scales. This paper provides a review of the effect of factors that influence flow and salt transport in STEs, evaluates current understanding on the interactions between these influences, and synthesizes understanding of drivers of nutrient, carbon, greenhouse gas, metal and organic contaminant fluxes to the ocean.Based on this review, key research needs are identified. While the effects of density and tides are well understood, episodic and longer-period forces as well as the interactions between multiple influences remain poorly understood. Many studies continue to focus on idealized nearshore aquifer systems and future work needs to consider real world complexities such as geological heterogeneities, and non-uniform and evolving alongshore and cross-shore morphology. There is also a significant need for multidisciplinary research to unravel the interactions between physical and biogeochemical processes in the STE, as most existing studies treat these processes in isolation. Better understanding of this complex and dynamic system can improve sustainable management of coastal water resources under the influence of anthropogenic pressures and climate change.

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“…These two transects were approximately perpendicular to the shoreline, but not parallel to each other, because the shoreline curved with the alongshore morphological variation. Further details of the field methods and data collection can be found in Zhang () and Zhang, Li, Erler, Santos, and Lockington ().…”

Section: Approach and Methodologymentioning

confidence: 99%

Effects of beach slope breaks on nearshore groundwater dynamics

Zhang

Erler

et al. 2017

Hydrological Processes

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Interactions between fresh groundwater and seawater affect significantly the nearshore pore water flow, which in turn influences the fate of nutrients and contaminants in coastal aquifers prior to discharge to the marine environment. Field investigations and numerical simulations were carried out to examine the groundwater dynamics in the intertidal zone of a carbonate sandy aquifer on the tropical island of Rarotonga, Cook Islands. The study site was featured by distinct cross‐shore slope breaks on the beach surface. Measured pore water salinities revealed different distributions under the influences of different beach profiles, inland heads, and tidal oscillations. Fresh groundwater was found to discharge around a beach slope break located in the middle area of the intertidal zone. The results indicate a strong interplay between the slope break beach morphology and tidal force in controlling the nearshore groundwater flow and solute transport. The fresh groundwater discharge location was largely determined by the beach morphology in combination with the tidal force. The nearshore groundwater flow can be very sensitive to beach slope breaks, which induce local circulation and flow instabilities. As slope breaks are a common feature of beaches around the world, these results have important, general implications for future studies of nutrients transport and transformations in nearshore aquifers and associated fluxes via submarine groundwater discharge.

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Effects of alongshore morphology on groundwater flow and solute transport in a nearshore aquifer

Cited by 33 publications

References 60 publications

Effects of episodic rainfall on a subterranean estuary

Effects of episodic rainfall on a subterranean estuary

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

Effects of beach slope breaks on nearshore groundwater dynamics

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