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Modeling Infiltration into Crusted Soils by the Green—Ampt Approach¹

ABSTRACT

The study deals with infiltration of water through a stable surface crust, wherein the water content at the crust-soil interface increases with time for a long period, and remains below the saturated value. An approximate Green-Ampt-type formulation derived from a physical basis, containing a time-dependent capillary drive term and a profile shape factor, is evaluated by comparisons to a similarity solution and a finite-difference numerical solution of the problem. The exact nature of the derived Green-Ampt formulation is established for early to intermediate stages for certain reasonable conditions. Calculations of cumulative infiltration with time made by the above approach, with the profile shape factor set equal to unity, were within tolerable error from the numerical solution results for one soil and a set of experimental data for another. A previously reported piecewise application of the conventional form of the Green-Ampt equation is also developed to enable its use from time zero, as an independent predictive method. This method, which includes some implicit correction for the profile shape, gave slightly better calculations of the cumulative infiltration. The above simple methods should also be applicable to related unsaturated flow problems, such as infiltration through a transient crust-seal resistance and into a layered soil having a fine material overlying a coarse material.

¹ Contribution from the USDA—ARS, Water Quality and Watershed Research Laboratory, P.O. Box 1430, Durant, OK 74701.

² Soil Scientist, USDA—ARS, Durant, OK 74701.

Received for publication June 21, 1982. Accepted for publication January 12, 1983.

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