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Numerical Simulations of One-Dimensional Infiltration into Layered Soils with the Richards Equation Using Different Estimates of the Interlayer Conductivity

^a Department of Civil and Environmental Engineering, University of Perugia, Perugia, Italy
^b Department of Agricultural Engineering, University of Naples Federico II, Portici (Naples), Italy

View larger version (26K): [in a new window]   Fig. 1. Computational grid near the interface between two soil layers, with schematic distributions of the pressure heads at a certain time during the transient flow.

View larger version (23K): [in a new window]   Fig. 2. (a) Pressure head and (b) water content distributions at selected times as computed with the analytical model of Srivastava and Yeh (1991) for a two-layer soil profile assuming an infiltration scenario with qini = 4.54 x 10-4 cm h-1 and qfin = 0.95 cm h-1. The horizontal bold line indicates the location of the interface between the two soil layers.

View larger version (31K): [in a new window]   Fig. 3. Distributions of the relative local error in , , with respect to Srivastava and Yeh's analytical solution for the uppermost part of the flow domain and for four different finite-differences models: (a) H-IL model, (b) H-GM model, (c) THT-GM model, and (d) MIX-GM model.

View larger version (33K): [in a new window]   Fig. 4. Relative mass balance error, W, as a function of time, t, obtained with four finite difference models. The H-IL model is the h-based numerical model with Eq. [5] for computing the interlayer conductivity. The H-GM, THT-GM, and MIX-GM are the h-based, -based, and mixed formulations of the Richards equation, respectively, all using the geometric mean (Eq. [4]) as averaging criterion for computing the interlayer conductivity.

View larger version (29K): [in a new window]   Fig. 5. Pressure head distributions, h(z), at selected time, t, as computed with the analytical model of Srivastava and Yeh (1991) for a two-layer soil profile assuming an infiltration scenario with qini = 0.010 cm h-1 and qfin = 0.90 cm h-1. The horizontal bold line represents the location of the interface between the two soil layers.

View larger version (22K): [in a new window]   Fig. 6. Distributions of the local error in h, h, with respect to Srivastava and Yeh's analytical solution as obtained with the finite-elements HYDRUS model.

View larger version (47K): [in a new window]   Fig. 7. Relative flux, q/qfin, as a function of relative time, t/t*, obtained with the H-IL model at the interface and at the water table for three different values of parameter = L1/L2. Squares refer to = 1/3 (a), circles refer to = 3 (b), and triangles refer to = 9 (c). Open symbols represent conditions at the layer interface, whereas closed symbols represent conditions at the water table.