Numerical modeling of the effect of variation of boundary conditions on vadose zone hydraulic properties

Abstract

SUMMARYAn accurate estimation of hydraulic fluxes in the vadose zone is essential for the prediction of water, nutrient and contaminant transport in natural systems. The objective of this study was to simulate the effect of variation of boundary conditions on the estimation of hydraulic properties (i.e. water content, effective unsaturated hydraulic conductivity and hydraulic flux) in a one-dimensional unsaturated flow model domain. Unsaturated one-dimensional vertical water flow was simulated in a pure phase clay loam profile and in clay loam interlayered with silt loam distributed according to the third iteration of the Cantor Bar fractal object Simulations were performed using the numerical model Hydrus 1D. The upper and lower pressure heads were varied around average values of -55 cm for the near-saturation range. This resulted in combinations for the upper and lower constant head boundary conditions, respectively, of -50 and -60 cm, -40 and -70 cm, -30 and -80 cm, -20 and -90 cm, and -10 and -100 cm. For the drier range the average head between the upper and lower boundary conditions was set to -550 cm, resulting in the combinations -500 and -600 cm, -400 and -700 cm, -300 and -800 cm, -200 and -900 cm, and -100 and -1,000 cm, for upper and lower boundary conditions, respectively. There was an increase in water contents, fluxes and hydraulic conductivities with the increase in head difference between boundary conditions. Variation in boundary conditions in the pure phase and interlayered onedimensional profiles caused significant deviations in fluxes, water contents and hydraulic conductivities compared to the simplest case (a head difference between the upper and lower constant head boundaries of 10 cm in the wetter range and 100 cm in the drier range).Index terms: Numerical model, Hydrus 1D, uncertainty, boundary conditions, hydraulic conductivity, soil physics.( de -50 e -60 cm; -40 e -70 cm; -30 e -80 cm; -20 e -90 cm; e -10 e -100 cm, para

Internal heat source in the vadose zone: A comprehensive exploration through theoretical spectral analysis and practical application into thermal diffusivity and hydraulic flux in a Quaternary soil water layer

“…It assumes that the solution obtained can meet the specified tolerance level, given the spectral estimation of the observations aligns with the actual conditions at the study site. For a low permeability and faster flow in more permeable soils, the typical range of hydraulic flux may select 10 −6 to 10 −9 and 10 −4 to 10 −5 m/s, respectively (Jougnot et al, 2012; Kool et al, 1987; Leão & Gentry, 2011; Parker, 2003; Wilson, 1983).…”

“…It assumes that the solution obtained can meet the specified tolerance level, given the spectral estimation of the observations aligns with the actual conditions at the study site. For a low permeability and faster flow in more permeable soils, the typical range of hydraulic flux may select 10 À6 to 10 À9 and 10 À4 to 10 À5 m/ s, respectively (Jougnot et al, 2012;Kool et al, 1987;Leão & Gentry, 2011;Parker, 2003;Wilson, 1983). Table 1 and Figure 6a delineate the assessment of the internal heat source, considering thermal diffusivity and hydraulic flux within the framework of BC type 1, the specified depth, and notable spectral components within a controlled volume extending 1.2 m. The estimated internal heat (E) ranges from 10 À3 to 10 À5 C/s for diurnal and semi-diurnal patterns.…”