2006 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and the Department of Civil Engineering at the University of Mississippi. Additional details of research can be found in the report for the inhouse project 6408-13000-017-00D, Integrated Assessment and Analysis of Physical Landscape Processes That Impact the Management of Agricultural Watersheds, and for prior years in the reports for the terminated inhouse project 6408-12130-012-00D, Processes, Control, and Prediction of Erosion and Runoff on Upland Areas in Agricultural Watersheds, from which the agreement was funded. This project seeks to predict rain infiltration and subsurface flow for "real world" soil and slope conditions. A paper was prepared and published that considered hydrologic effects of subsurface flow on head-cut migration. Both infiltration and seepage through the vertical wall of the head-cut were considered, and expressions were obtained in terms of the head-cut migration velocity as a function of the seismic velocity, surface seal properties, and flow depth for the infiltration case, and in terms of the seepage force and seal critical length for the seepage case. Additional analyses were performed to describe infiltration into swelling/shrinking/cracking soils. The approach taken consisted of a two-component process of Darcian matrix flow in the soil medium and Hortonian flow on the vertical walls of a cracked soil that was subjected to a series of rainstorm events separated by drying periods. Mathematical relationships were found that predicted incipient ponding and the cumulative infiltration as a function of the rainfall intensity, crack morphology (depth, spacing, and width), and the soil water sorptivity.