Timescales of seawater intrusion and retreat

Lu, Chunhui; Werner, Adrian D.

doi:10.1016/j.advwatres.2013.05.005

Cited by 89 publications

(87 citation statements)

References 35 publications

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“…This is likely due to the change in the model's aspect ratio (the ratio of aquifer length to thickness), whereby decreasing this ratio (due to the increase of h s ) enhances SWI and therefore WTS. This is in agreement with the result of Werner and Simmons [] and Lu and Werner [] who showed that the extent of SWI is larger in a thicker coastal aquifer, in response to the same boundary head differences. Interestingly, x tip increased and x toe decreased with higher values of α L (Figure c).…”

Section: Resultsmentioning

confidence: 99%

Water table salinization due to seawater intrusion

Badaruddin

Werner

Morgan

2015

Water Resources Research

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Seawater intrusion (SWI) is a significant threat to freshwater resources in coastal aquifers around the world. Previous studies have focused on SWI impacts involving salinization of the lower domain of coastal aquifers. However, under certain conditions, SWI may cause salinization of the entire saturated zone of the aquifer, leading to water table salinization (WTS) in unconfined aquifers by replacing freshwater within the upper region of the saturated zone with seawater, thereby posing a salinity threat to the overlying soil zone. There is presently limited guidance on the extent to which WTS may occur as a secondary impact of SWI. In this study, physical experiments and numerical modeling were used to explore WTS associated with SWI in various nontidal, unconfined coastal aquifer settings. Laboratory experiments and corresponding numerical simulations show that significant WTS can occur under active SWI (i.e., the freshwater hydraulic gradient slopes toward the land) because the cessation of freshwater discharge to the sea and the subsequent landward flow across the entire sea boundary eventually lead to water table salinities approaching seawater concentration. WTS during active SWI is larger under conditions of high hydraulic conductivity, rapid SWI, high dispersivity and for deeper aquifers. Numerical modeling of four published field cases demonstrates that rates of WTS of up to 60 m/yr are plausible. Under passive SWI (i.e., the hydraulic gradient slopes toward the sea), minor WTS may arise as a result of dispersive processes under certain conditions (i.e., high dispersivity and hydraulic conductivity, and low freshwater discharge). Our results show that WTS is probably widespread in coastal aquifers experiencing considerable groundwater decline sustained over several years, although further evidence is needed to identify WTS under field settings.

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Section: Resultsmentioning

confidence: 99%

Water table salinization due to seawater intrusion

Badaruddin

Werner

Morgan

2015

Water Resources Research

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“…Both SGD and the salt distribution attributed to a particular force must be determined with consideration of the influence of other forces both at the present and in the past. The response of SGD and saltwaterfreshwater mixing zone to the different forces is not instantaneous but delayed [Michael et al, 2005;Lu and Werner, 2013;Robinson et al, 2014;Xin et al, 2014;Liu et al, 2016;Yu et al, 2017]. This complicates the assessment of interactions between multiple forces.…”

Section: Interacting Effects Among Forcingmentioning

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

202

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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“…It is often difficult to derive a clear understanding of the mechanisms affecting SWI directly from field‐based investigation (Werner et al, ). The challenge of measuring and quantifying coastal aquifer hydrodynamics and SWI in field sites has promoted the use of laboratory and numerical modelling tools to gain a valuable insight into SWI response to various geological and/or hydrological stresses, such as (a) change in seaward freshwater discharge resulting from fluctuations at the inland head boundary (Abdoulhalik & Ahmed, ; Abdoulhalik & Ahmed, ; Abdoulhalik, Ahmed, & Hamill, ; Goswami & Clement, ; Lu & Werner, ; Robinson, Ahmed, & Hamill, ; Robinson, Hamill, & Ahmed, ) in head‐controlled systems or from variations of the regional freshwater flux (Chang & Clement, ; Stoeckl & Houben, ; Stoeckl, Houben, & Dose, ) in flux‐controlled systems and (b) SLR (Hussain & Javadi, ; Morgan, Bakker, & Werner, ; Morgan, Stoeckl, Werner, & Post, ).…”

Section: Introductionmentioning

confidence: 99%

Transience of seawater intrusion and retreat in response to incremental water‐level variations

Abdoulhalik

Ahmed

2018

Hydrological Processes

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This paper provides for the first time an experimental study where the impact of sea‐level fluctuations and inland boundary head‐level variations on freshwater–saltwater interface toe motion and transition zone dynamics was quantitatively analysed under transient conditions. The experiments were conducted in a laboratory flow tank where various (inland and coastal) head changes were imposed to the system and the response of the key seawater intrusion parameters was analysed with high spatial and temporal resolution. Two homogeneous aquifer systems of different grain size were tested. The numerical code SEAWAT was used for the validation. The results show that in cases of sea‐level variations, the intruding wedge required up to twice longer time to reach a new steady‐state condition than the receding wedge, which thereby extend the theory of timescale asymmetry between saltwater intrusion and retreat processes in scenarios involving sea‐level fluctuations. The intruding and receding rates of the saltwater wedge were respectively similar in the scenario involving sea‐level and the freshwater‐level changes, despite change in transmissivity. The results show that, during the intrusion phase, the transition zone remains relatively insensitive, regardless of where the boundary head change occurs (i.e., freshwater drop or sea‐level rise) or its magnitude. By contrast, a substantial widening of the transition zone was observed during the receding phase, with almost similar amplitude in the scenario involving a rise of the freshwater level compared with that caused by a drop of the saltwater level, provided that an equivalent absolute head change magnitude was used. This transition zone widening (occurring during saltwater retreat) was greater and extended over longer period in the low hydraulic conductivity aquifer, for both freshwater‐level rise and sea‐level drop scenarios. The concentration maps revealed that the widening mechanism was also enhanced by the presence of some freshwater sliding and into the wedge during saltwater retreat, which was thereafter sucked upward towards the interface because of density difference effects.

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Timescales of seawater intrusion and retreat

Cited by 89 publications

References 35 publications

Water table salinization due to seawater intrusion

Water table salinization due to seawater intrusion

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

Transience of seawater intrusion and retreat in response to incremental water‐level variations

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