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Simplified Method to Estimate the Green–Ampt Wetting Front Suction and Soil Sorptivity with the Philip–Dunne Falling-Head Permeameter

^a Instituto Canario Investigaciones Agrarias (ICIA), Dep. Suelos y Riegos, Apdo. 60 La Laguna, 38200 La Laguna, Spain
^b Instituto Tecnológico Agrario de Castilla y León, Apdo. 172, 47080 Valladolid, Spain
^c Agricultural and Biological Engineering Dep., University of Florida, 101 Frazier Rogers Hall, P.O. Box 110570, Gainesville, FL 32611-0570

View larger version (28K): [in a new window]   Fig. 1. Geometrical analog of the Philip–Dunne falling-head permeameter.

View larger version (16K): [in a new window]   Fig. 2. (a) tmax/tmed vs. , and (b) tmax/tmed vs. max relationships for the 308 measurements performed in eight different soils (represented by different symbols). Insert in (b) represents tmax/tmed vs. max values where is positive.

View larger version (10K): [in a new window]   Fig. 3. Goodness of fit of both derived equations (Eq. [8] and [9]) to compute Ks, , and S evaluated by comparing these with the solution obtained by solving numerically the full system (Eq. [6]).

View larger version (10K): [in a new window]   Fig. 4. Plot of the data pairs (tmax/tmed, > 0) and the curve tmax/tmed = f (, ) obtained from Eq. [6] for two different water content increments: = 0.05m3 m–3 (lower curve) and = 0.5 m3 m–3 (upper curve). Notice that the axes are inverted with respect to Fig. 2.

View larger version (34K): [in a new window]   Fig. 5. Sensitivity analysis of Ks, , and S (OY axes) to variations of parameters: ho, tmax, tmed, , and gc (represented by different line types) within the interval [–20%, 20%], for various initial ratios tmax/tmed = 2.61, 3.74, and 5.38 (from left to right). In those cases where the parameter combination yielded < 0, the solving algorithm ceases to compute and thereby no SC was calculated. The sensitivity coefficient, SC, represents the percentage of variation with respect to the initial value (OY axes).

View larger version (35K): [in a new window]   Fig. 6. Sensitivity analysis of Ks, , and S (OY axes) to variations of parameters: ho, tmax, tmed, , and gc (represented by different line types) within the interval [–20%, 20%], for an initial ratio tmax/tmed = 5.38 with different initial values of = 0.10, 0.26, and 0.35 m3 m–3 (from left to right). In those cases where the parameter combination yielded < 0, the solving algorithm ceases to compute and thereby no SC was calculated. The sensitivity coefficient, SC, represents percentage of variation with respect to the initial value (OY axes).