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

Abstract

[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,

Effects of vadose zone on groundwater table fluctuations in unconfined aquifers

“…Using this equation, various numerical and analytical studies have been conducted to investigate the groundwater table fluctuations affected by various geometric and oceanic forcing factors, e.g., sloping beach (Nielsen, 1990) and spring-neap tides (Li et al, 2000c). However, these studies neglected the effect of vadose zone, which is expected to alter the water movement in the saturated zone and thus groundwater table fluctuations (Cardenas, 2010;Cartwright et al, 2005;Moench, 2008). Situated above the phreatic surface (water table), the vadose zone includes a capillary fringe (fully saturated zone with pressure less than the atmospheric pressure) and unsaturated zone (partly saturated zone with pressure also less than the atmospheric pressure).…”

Measurement and modeling of moisture content above an oscillating water table: implications for beach surface moisture dynamics

“…Childs and Poulovassilis, 1962;Childs, 1969;Raats and Gardner, 1974;Kessler and Rubin, 1987); however, several recent studies have demonstrated that when hysteresis is accounted for it is possible to obtain significantly improved simulations of observed capillary water flows above a fluctuating water table (i.e. Hinz, 1998;Raubenheimer et al, 1999;Nielsen and Perrochet, 2000;Werner and Lockington, 2003;Cartwright et al, 2005Cartwright et al, , 2009. Our understanding of the influence of this phenomenon on beach surface moisture dynamics remains incomplete.…”

Characterizing the hydraulic properties of unsaturated sand considering various porosities and drying‐wetting paths of the retention curve

“…Nielsen and Perrochet () and Cartwright et al . () experimentally and numerically investigated the interaction of water table and capillary fringes, while considering the hysteresis implicitly. Cavazza et al .…”