Flow dynamics and age stratification of freshwater lenses: Experiments and modeling

Stoeckl, Leonard; Houben, Georg

doi:10.1016/j.jhydrol.2012.05.070

Cited by 68 publications

(63 citation statements)

References 30 publications

(40 reference statements)

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“…The stratification pattern of groundwater ages as depicted in Fig.7 was confirmed by sand tank experiments by Stoeckl and Houben (2012). Field evidence of groundwater age stratification in coastal dunes is available from Stuyfzand (1993), Röper et al (2012) and Houben et al (2014).…”

Section: Modeling Symmetrical Free Isolated Lensessupporting

confidence: 53%

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Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

Stuyfzand

2016

J Coast Conserv

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Observations are reported on (i) groundwater recharge rates under various types of vegetation as measured with megalysimeters in the dunes, (ii) freshwater lenses along the Dutch North Sea coast in the early 1900s, and (iii) rainwater lenses that develop on top of laterally migrating, artificially recharged riverwater. Subsequently analytical methods are presented to estimate annual natural groundwater recharge as function of rainfall and vegetation, and to calculate the size, shape and transition zone of freshwater lenses on saline groundwater and rainwater lenses on infiltrated riverwater. An empirical correction factor, based on the hydraulic resistance of an aquitard within the freshwater lens, is proposed to account for the frequently observed reduction of the GhybenHerzberg ratio of 40. This factor raises the groundwater table, reduces the depth of the fresh/salt interface and increases the lens formation time. The suite of methods offers a tool box for knowledge based water management of dune systems, by rapidly predicting: (i) more or less autonomous changes due to sealevel rise, climate change and vegetation development; and (ii) the potential (side) effects of interventions. Knowing what happened or will happen to the fresh water lens or a rainwater lens is important, because changes impact on important natural habitat parameters such as salinity, depth to groundwater table, decalcification rate (and thus on pH, Ca/Al, PO 4 , NH 4 ) and nutrient availability, and on drinking water supply. The analytical models are applied to predict effects of sealevel rise, coastal progradation, vegetation changes, and increased temperature of coastal air and river water to be infiltrated.

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Section: Modeling Symmetrical Free Isolated Lensessupporting

confidence: 53%

“…Eq.6A performs very well not only on site 20 (B = 475 m), but also in the small sized sand tank experiments (0.8 m) by Stoeckl and Houben (2012).…”

Section: Modeling Symmetrical Free Isolated Lensesmentioning

confidence: 84%

Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

Stuyfzand

2016

J Coast Conserv

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“…Because recharge is the main driver of lens formation and maintenance, when the rate of recharge is reduced, the response time of the hydrogeological system is also reduced. This has been observed in laboratory experiments (Stoeckl and Houben, 2012) whereby the lens takes longer to reach steady state when there is reduced input (i.e., specified flux or concentration boundaries) to the system. Therefore, areas where there is less recharge, such as the southern regions of Andros Island, are expected to take longer to react and adapt to stresses to the hydrogeological system.…”

Section: Long-acting Stressorsmentioning

confidence: 78%

From days to decades: numerical modelling of freshwater lens response to climate change stressors on small low-lying islands

Holding

Allen²

2015

Hydrol. Earth Syst. Sci.

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Abstract. Freshwater lenses on small islands are vulnerable to many climate change-related stressors, which can act over relatively long time periods, on the order of decades (e.g., sea level rise, changes in recharge), or short time periods, such as days (storm surge overwash). This study evaluates the response of the freshwater lens on a small lowlying island to various stressors. To account for the varying temporal and spatial scales of the stressors, two different density-dependent flow and solute transport codes are used: SEAWAT (saturated) and HydroGeoSphere (unsaturated/saturated). The study site is Andros Island in the Bahamas, which is characteristic of other low-lying carbonate islands in the Caribbean and Pacific regions. In addition to projected sea level rise and reduced recharge under future climate change, Andros Island experienced a storm surge overwash event during Hurricane Francis in 2004, which contaminated the main wellfield. Simulations of reduced recharge result in a greater loss of freshwater lens volume (up to 19 %), while sea level rise contributes a lower volume loss (up to 5 %) due to the flux-controlled conceptualization of Andros Island, which limits the impact of sea level rise. Reduced recharge and sea level rise were simulated as incremental instantaneous shifts. The lens responds relatively quickly to these stressors, within 0.5 to 3 years, with response time increasing as the magnitude of the stressor increases. Simulations of the storm surge overwash indicate that the freshwater lens recovers over time; however, prompt remedial action can restore the lens to potable concentrations up to 1 month sooner.

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“…Nevertheless, several experimental studies have investigated SWI for an array of different problems in synthetic homogeneous aquifers without quantifying the WMZ (Goswami and Clement, 2007;Werner et al, 2009;Luyun et al, 2011;Shi et al, 2011;Jakovovic et al, 2012;Stoeckl and Houben, 2012;Morgan et al, 2013;Clement, 2012, 2013;Dose et al, 2014). Werner et al (2009) investigated laboratory scale saltwater upconing at extraction wells and compared the results to an analytical sharp interface solution.…”

Section: Introductionmentioning

confidence: 99%

Experimental saltwater intrusion in coastal aquifers using automated image analysis: Applications to homogeneous aquifers

Robinson

Ahmed

Hamill

2016

Journal of Hydrology

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This paper presents the applications of a novel methodology to quantify saltwater intrusion parameters in laboratory-scale experiments. The methodology uses an automated image analysis procedure, minimizing manual inputs and the subsequent systematic errors that can be introduced. This allowed the quantification of the width of the mixing zone which is difficult to measure in experimental methods that are based on visual observations. Glass beads of different grain sizes were tested for both steady-state and transient conditions. The transient results showed good correlation between experimental and numerical intrusion rates. The experimental intrusion rates revealed that the saltwater wedge reached a steady state condition sooner while receding than advancing. The hydrodynamics of the experimental mixing zone exhibited similar traits; a greater increase in the width of the mixing zone was observed in the receding saltwater wedge, which indicates faster fluid velocities and higher dispersion. The angle of intrusion analysis revealed the formation of a volume of diluted saltwater at the toe position when the saltwater wedge is prompted to recede. In addition, results of different physical repeats of the experiment produced an average coefficient of variation less than 0.18 of the measured toe length and width of the mixing zone. KeywordsSaline water intrusion; Intrusion angle; Width of the mixing zone; Light to concentration conversion.

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Flow dynamics and age stratification of freshwater lenses: Experiments and modeling

Cited by 68 publications

References 30 publications

Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

Observations and analytical modeling of freshwater and rainwater lenses in coastal dune systems

From days to decades: numerical modelling of freshwater lens response to climate change stressors on small low-lying islands

Experimental saltwater intrusion in coastal aquifers using automated image analysis: Applications to homogeneous aquifers

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