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SPECIAL SECTION: ZNS'03 VADOSE ZONE RESEARCH

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
^* Corresponding author (cregalad{at}icia.es)

Received 5 July 2004.

Wetting front suction and soil sorptivity (S) are relevant parameters to water movement in the vadose zone. Both may be estimated with the Philip–Dunne falling-head permeameter, given the moisture increment () and measured times (t_med and t_max) during an infiltration event. Previous studies have shown that the Philip–Dunne falling head permeameter can be used for estimating saturated hydraulic conductivity (K_s), but its potential to estimate the soil's sorptivity has received little attention. We investigate the ability of the Philip–Dunne method to estimate S and the Green–Ampt's suction at the wetting front, , by performing a parameter sensitivity analysis, focusing on the boundary conditions that limit the search space of physically sound solutions, and studying the shape factors used in Philip's analysis to reduce the three-dimensional flux of water in the soil to one dimension. Finally, a useful approximate solution is provided that allows computing both K_s and the Green–Ampt's suction at the wetting front, , (and hence the macroscopic capillary length parameter, *) from only two infiltration times, t_med and t_max, without having to resort to such a costly measurement as the soil moisture increment, , required by the original method.