Submitted to: Federal Interagency Hydrologic Modeling Conference
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 10, 1998
Publication Date: N/A
Interpretive Summary: Infiltration prediction is often complicated by the changing nature of the soil matrix. For a rigid soil matrix infiltration can readily be analytical or numerical solutions of Richard's equation. For a non rigid soil matrix, empirical solutions are needed which depend on the initial and boundary conditions. One such class of soils are expansive soils, which depending on the type and amount of clay minerals, may develop large cracks upon drying. During a rainstorm a sizeable amount of the incident rain will enter into the profile. In this article, experiments will be discussed in which an expansive soil, a Sharkey clay, will be subjected to a series of rainstorms of constant characteristics. Following each storm, the soil will be allowed to dry and to crack. The infiltration relationships following each drying period will be discussed. A model will be developed that describes the rain infiltration process into two stages. The preponding stage in which most of the rainfall enters the soil through the cracks and a post-ponding stage in which infiltration mainly occurs as matrix flow. This paper focuses on the preponding stage and estimates incipient ponding as a function of rainfall intensity, crack depth, and crack spacing.
Certain analytical solutions of rain infiltration into dry cracked soil are presented with particular emphasis on the calculations of ponding time. The morphology of cracks is identified by a rather simple geometric pattern whose scale, however, leads to a meaningful expression for ponding time. The analysis utilizes the wetting front solutions of horizontal diffusion governed by Richards' equation as developed by the present authors in a recent study. The soil matrix diffusion characteristics are represented by a set of two parameters given by Ahuja and Swartzendruber (1972). The ponding time estimates appear to agree well with the data currently being obtained at the National Sedimentation Laboratory for Mississippi Delta clay soils.