EFFECTS OF AIR COMPRESSION AND COUNTERFLOW ON INFILTRATION INTO SOILS

Infiltration into soils is affected by several factors, including the soil-air pressure. Soil air may become compressed between a confining layer (water table) and a nearly saturated surface soil. Compressed and counterflowing air substantially reduce's soil infiltration rates resulting in potential practical problems of excess runoff and erosion. Using results from laboratory column studies, we describe a simple set of infiltration equations to predict infiltration rate and cumulative infiltration. Infiltration rates progressively declined in bounded soil columns until the soil-air pressure head exceeded the sum of the ponded water depth and the capillary driving head at the wetting front. After a brief transition period during which stable air channels formed in the porous media, the infiltration rate approached a constant value. We demonstrate a simple method to predict this stable infiltration Tate based on the permeability-saturation relationship for the soil. Finally, we illustrate that the reduction in cumulative infiltration in bounded soils is roughly proportional to the water-table depth, and that this reduction is greater in sands as compared to loamy soils.