Infiltration in Shallow Water Table Environments: Simple Two-Phase Model Accounting for Air Compression and Counterflow

Abstract

AbstractA new method is introduced to simulate air compression and counterflow during infiltration into a shallow water table. The method retains the simplicity of Green and Ampt but with one added term, the air pressure resistance below the wetting front. The method differs from existing methods because it couples air compression and counterflow flux dynamically with infiltration. The new method is original and simple, yet it allows the extension of Green and Ampt to simulate infiltration into shallow water environments or a shallow impervious zone where soil-air pressurization is likely to develop. In shallow water table environments, it is shown that neglecting counterflow of air will cause a rapid decline in infiltration due to unrealistic buildup of air pressure below the wetting front. Accounting for air compression and counterflow seemed necessary to bridge between Hortonian (infiltration excess) and Dunne (saturation excess) mechanisms of runoff.