Constant‐Flux Infiltration from a Hemispherical Cavity

Existing theories of Raats, Parlange, and Warrick describing constant‐flux absorption and infiltration from hemispherical cavities are reviewed. A simple theory for absorption is derived, using the flux‐concentration relation of Philip. Three‐dimensional infiltration experiments are described that were used to test these theories. The results showed that infiltration at 360 ml/h into a 4‐mm‐radius hemispherical cavity in a repacked fine sand was described quite well by the simple absorption theory for the first 100 min. Beyond this time, at this flux, the effects of gravity became evident, as expected from a comparison of the matric and gravitational potential gradients. The nonlinear, steady‐state infiltration theory of Raats gave reasonable estimates of the water content profiles behind the wet front. The linearised (constant diffusivity) theory of Warrick was of no value in this context. The success of the Raats theory adds some credence to the use in trickle irrigation design of the Wooding's theory which describes infiltration from a circular pond on the basis of the same assumptions.