Experimental observations of watertable waves in an unconfined aquifer with a sloping boundary

Cartwright, Nick; Nielsen, Peter; Li, Ling

doi:10.1016/j.advwatres.2004.08.006

Cited by 77 publications

(53 citation statements)

References 15 publications

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“…The present data however has highlighted significant limitations in this approach, particularly in the high-frequency limit. Limitations of the model when applied to the 2D case of a propagating water table wave have also been identified [Cartwright et al, 2003[Cartwright et al, , 2004. As such it is suggested that further development of the problem be directed toward improving the understanding of the processes involved in the coupling of the saturated zone with the capillary fringe.…”

Section: Influence Of Proximity To the Sand Surfacementioning

confidence: 99%

“…Cartwright et al [2004] present data from the same sand column where all other parameters were kept constant and the sand surface lowered incrementally for each test, thereby truncating the capillary fringe. The results showed a significant reduction in jn w j of up to three orders of magnitude (relative to the truncation free value) as the fringe became increasingly truncated (see their Figure 8).…”

Section: Influence Of Proximity To the Sand Surfacementioning

confidence: 99%

“…Therefore the empirical complex effective porosity model, equation (5), is only valid where the water table is deep enough such that truncation effects are negligible. As a guide the experiments of Cartwright et al [2004] revealed that truncation effects only became apparent when the sand surface (z s ) was approximately half a capillary fringe height Nielsen and Perrochet [2000] showed that using the Green and Ampt [1911] approximation of the fringe leads to the following linear frequency response function for the water table in the sand column,…”

Section: Influence Of Proximity To the Sand Surfacementioning

confidence: 99%

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Influence of capillarity on a simple harmonic oscillating water table: Sand column experiments and modeling

Cartwright

Nielsen

Perrochet

2005

Water Resources Research

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[1] Comprehensive measurements of the water table response to simple harmonic forcing at the base of a sand column are presented and discussed. In similar experiments, Nielsen and Perrochet (2000) observed that fluctuations in the total moisture were both damped and lagged relative to the water table fluctuations. As a result, the concept of a complex effective porosity was proposed as a convenient means to account for the damping and phase lag through its magnitude and argument, respectively. The complex effective porosity then enables simple analytical solutions for the water table (and total moisture) dynamics including hysteresis. In this paper, these previous experiments are extended to cover a wider range of oscillation frequencies and are conducted for three well-sorted materials with median grain diameters of 0.082, 0.2, and 0.78 mm, respectively. In agreement with existing theory, the influence of the capillary fringe is shown to increase with the oscillation frequency. However, the complex effective porosity model corresponding to the classical Green and Ampt (1911) capillary tube approximations is shown to be inadequate when compared to the data. These limitations are overcome by the provision of an empirical, frequency-dependent complex effective porosity model fit to the data. Using measured moisture retention parameters, numerical simulation of the data solving a nonhysteretic van Genuchten-Richards' equation type model is unable to replicate the observations. Existing results of a hysteretic numerical model are shown to be in good agreement with the extended database.Citation: Cartwright, N., P. Nielsen, and P. Perrochet (2005), Influence of capillarity on a simple harmonic oscillating water table: Sand column experiments and modeling, Water Resour. Res., 41, W08416,

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Section: Influence Of Proximity To the Sand Surfacementioning

confidence: 99%

Section: Influence Of Proximity To the Sand Surfacementioning

confidence: 99%

Section: Influence Of Proximity To the Sand Surfacementioning

confidence: 99%

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Influence of capillarity on a simple harmonic oscillating water table: Sand column experiments and modeling

Cartwright

Nielsen

Perrochet

2005

Water Resources Research

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“…In the vicinity of the exit point, the capillary fringe will be truncated by the sand surface (see zone A of Figure 1), which will also lead to a further reduction in the storage coefficient [e.g., Gillham, 1984]. Cartwright et al [2004b] presented sand column data in which the storage coefficient was further reduced by up to a factor 4 with increasing degrees of truncation. Combining the reduction described by equation (5) along with a conservative factor of 2 reduction for truncation effects leads to the reduced aquifer storage coefficient,…”

Section: Water Table Exit Point Dynamicsmentioning

confidence: 99%

Swash‐aquifer interaction in the vicinity of the water table exit point on a sandy beach

et al. 2006

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[1] The coupling of sandy beach aquifers with the swash zone in the vicinity of the water table exit point is investigated through simultaneous measurements of the instantaneous shoreline (swash front) location, pore pressures and the water table exit point. The field observations reveal new insights into swash-aquifer coupling not previously gleaned from measurements of pore pressure only. In particular, for the case where the exit point is seaward of the observation point, the pore pressure response is correlated with the distance between the exit point and the shoreline in that when the distance is large the rate of pressure drop is fast and when the distance is small the rate decreases. The observations expose limitations in a simple model describing exit point dynamics which is based only on the force balance on a particle of water at the sand surface and neglects subsurface pressures. A new modified form of the model is shown to significantly improve the model-data comparison through a parameterization of the effects of capillarity into the aquifer storage coefficient. The model enables sufficiently accurate predictions of the exit point to determine when the swash uprush propagates over a saturated or a partially saturated sand surface, potentially an important factor in the morphological evolution of the beach face. Observations of the shoreward propagation of the swash-induced pore pressure waves ahead of the runup limit shows that the magnitude of the pressure fluctuation decays exponentially and that there is a linear increase in time lags, behavior similar to that of tidally induced water table waves. The location of the exit point and the intermittency of wave runup events is also shown to be significant in terms of the shore-normal energy distribution. Seaward of the mean exit point location, peak energies are small because of the saturated sand surface within the seepage face acting as a ''rigid lid'' and limiting pressure fluctuations. Landward of the mean exit point the peak energies grow before decreasing landward of the maximum shoreline position.

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“…They showed that the effect of beach slope is important for predicting the watertable elevation. Recent field observations from exposed coasts have shown that wave forcing can also have a non-negligible impact on aquifer circulation (Cartwright et al, 2004b), which in turn may affect sediment transport and beach profile changes. Additional discussion of the mathematical modeling approaches 7 that have been used to simulate beach aquifers and their interaction with nearshore motion were summarized by Horn (2006) and Bakhtyar et al (2009a).…”

Section: Introductionmentioning

confidence: 99%

Numerical experiments on interactions between wave motion and variable-density coastal aquifers

Bakhtyar

Barry

Brovelli

2012

Coastal Engineering

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A comprehensive two-dimensional (cross-shore) process-based numerical model of nearshore hydrodynamics (based on the Navier-Stokes equations, k-ε turbulence closure and the Volume-Of-Fluid method), beach morphology, and variable-density groundwater flow (SEAWAT-2000) was developed. This model, which was applied at the field scale, relaxes simplifications in existing models that do not include such detailed mechanistic descriptions. Numerical experiments were conducted to investigate the effects of varying aquifer, beach and wave characteristics (e.g., inland groundwater head, sand grain size, different wave heights and periods) on the coupled system. Spilling and plunging breakers on dissipative and intermediate beaches were simulated. For a given set of boundary conditions, the model was run for 1 y without the hydrodynamic sub-model to achieve a realistic salt-/freshwater interface. Then, the hydrodynamic component was run for 15 min and the model results analyzed. The main features considered were groundwater circulation, saltwater wedge position, in/exfiltration across the beach face, and beach morphology. The predictions of the numerical model agree well with existing understanding and experimental measurements. For an inland watertable that is lower than the still water level (SWL), such that the groundwater flow is mainly landward, on both coarse and fine sand beaches the addition of wave motion moves the saltwater wedge further landward. For an inland watertable that is higher than the SWL, the opposite behavior occurred. The numerical experiments showed that more sediment transport takes place on intermediate beaches than on dissipative beaches. In addition, beach profile variations are greater under plunging breakers, while coarse sand beaches are steeper than fine sand beaches for the same wave conditions. There is a strong correlation between in/exfiltration and beach face deposition/erosion for the coarse beaches, while in/exfiltration has a slight effect on sediment transport for fine beaches. The model is capable of simulating the short-term evolution of foreshore profile changes, and beach 3 watertable and saltwater wedge movement due to interactions between wave motion and coastal groundwater. IntroductionMost previous investigations concerned with modeling of interactions between ocean water and coastal groundwater focused on tide-induced watertable fluctuations, neglecting high-frequency wave-induced oscillations and variable-density groundwater flow (e.g., Teo et al., 2003;Brovelli et al., 2007;Robinson et al., 2007bRobinson et al., , 2009Slooten et al., 2010;Li et al., , 2007Xin et al., 2010). However, given the interplay of mechanisms inherent in coastal processes -mixing of fresh-and seawater driven by waves, sediment transport and beach profile changes -it is not possible to extrapolate readily existing results to realistic coastal zone behavior.Waves in the nearshore zone are an important forcing on sediments and groundwater behavior. While waves induce instantaneous pore wat...

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Experimental observations of watertable waves in an unconfined aquifer with a sloping boundary

Cited by 77 publications

References 15 publications

Influence of capillarity on a simple harmonic oscillating water table: Sand column experiments and modeling

Influence of capillarity on a simple harmonic oscillating water table: Sand column experiments and modeling

Swash‐aquifer interaction in the vicinity of the water table exit point on a sandy beach

Numerical experiments on interactions between wave motion and variable-density coastal aquifers

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