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A Conceptual Model of Unstable Flow in Unsaturated Soil during Redistribution

^a Department of Environmental Sciences, University of California, Riverside, CA 92521
^b Department of Environmental Sciences, Calif. State Univ. Fresno, CA 93740

View larger version (46K): [in a new window]   Fig. 1. Fingering occurring in homogeneous soil during redistribution in the Hele–Shaw experiments of Wang et al. (2003a). Region illustrated is a subset of the 1 by 1 m area of the chamber.

View larger version (82K): [in a new window]   Fig. 2. Development of a fluid instability during redistribution, when the pressure distribution decreases toward the surface. When the front advances ahead at one location, the pressure distribution above it shifts downward, creating a lateral flow gradient from adjacent regions. Darker red color indicates wetter soil at higher matric potential.

View larger version (31K): [in a new window]   Fig. 3. Profile characteristics at the beginning (top) and end (bottom) of preferential flow. Darker red color indicates wetter soil at higher matric potential.

View larger version (18K): [in a new window]   Fig. 4. Outflow simulated with the two-dimensional Richards equation through apertures of different diameter (symbols) and gravity flow model Eq. [10] (line). Initial condition is profile produced by constant flux infiltration to a depth of 10 cm.

View larger version (16K): [in a new window]   Fig. 5. Equilibrium finger depth reached during redistribution as a function of infiltration rate. Curves were calculated with Eq. [6] through [9].

View larger version (16K): [in a new window]   Fig. 6. Finger shapes formed in sandy soil during redistribution following infiltration at different flux ratios Rs = i/Ks.

View larger version (11K): [in a new window]   Fig. 7. Finger depth reached as a function of time for the sandy soil following an infiltration at Rs = 0.25, calculated with Eq. [10] through [13]. Equilibrium position is shown as a dashed line.

View larger version (23K): [in a new window]   Fig. 8. Matric potential–water content curves calculated for the four soils, using the model Eq. [15] and the parameters in Table 1.