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Analytical Solutions for Vertical Flow in Unsaturated, Rooted Soils with Variable Surface Fluxes

^a Agric. Research and Extension Center, Texas A&M Univ., El Paso, TX 79927, USA
^b Hydrology, Geochemistry, and Geology Group (EES-6), Los Alamos National Lab., Los Alamos, NM 87545

View larger version (11K): [in a new window]   Fig. 1. Schematic of hypothetical water content () distribution in unsaturated soils. s is the water content at saturation, r is the residual water content, ET denotes evapotranspiration through root water uptake, q1 is time-dependent varying surface flux, and q(z, t) is water flow below soil surface. Note that both ET and q are positive upward.

View larger version (24K): [in a new window]   Fig. 2. Wetting profiles of (a) pressure head and (b) water content for soils without root water uptake ( = 0.01 cm–1).

View larger version (23K): [in a new window]   Fig. 3. Wetting profiles of (a) pressure head and (b) water content for soils without root water uptake ( = 0.1 cm–1).

View larger version (25K): [in a new window]   Fig. 4. Comparison of wetting profiles in rooted soils under constant surface flux (q1 = –0.9 cm h–1). (a) = 0.01 cm–1, S0 = 0.02 h–1. (b) = 0.1 cm–1 and S0 = 0.0025 h–1.

View larger version (27K): [in a new window]   Fig. 5. Comparison of soil water distribution in rooted soils under varying surface fluxes q1(t). (a) = 0.01 cm–1 and S0 = 0.02 h–1. (b) = 0.1 cm–1 and S0 = 0.0025 h–1. (c) Exponential surface input function.

View larger version (19K): [in a new window]   Fig. 6. Temporal development of water flows. (a) = 0.01 cm–1, S0 = 0.02 h–1, and k = 0. (b) = 0.01 cm–1, S0 = 0.02 h–1, and k = –0.1. (c) = 0.1 cm–1, S0 = 0.0025 h–1, and k = 0. (d) = 0.1 cm–1, S0 = 0.0025 h–1, and k = –0.1. Infiltration (q1) is in thick solid curves, flow at interface between root zone and subsoil (q2) in thin solid curves, and flow near the water table (q3) in dashed curves. Note that k is a constant in q1(t) = q0 + exp(kt), = –0.8 cm h–1.