INFILTRATION FROM A SURFACE POINT-SOURCE AND DRIP IRRIGATION .2. AN APPROXIMATE TIME-DEPENDENT SOLUTION FOR WET-FRONT POSITION

Raats' [1971] steady state theory is here extended to provide an appro ximate analysis of the transient pattern of wetting around a point sou rce. The assumption that a steady state regime prevails behind the wet front and the use of the Clothier [1984] and Philip [1984] theories o n water movement along the streamlines allows an approximate transient solution for surface point source infiltration to be developed. This procedure was previously tested against absorption theory and laborato ry experiments [Revel et al., 1995], but now this new analysis is eval uated via a field test. The vertical elongating influence of gravity i s found to be well predicted. Application of this analysis to design p urposes is also mentioned. The role of the macroscopic characteristic capillary length of unsaturated flow, lambda(c), is highlighted by thi s approximate solution. Finally, we propose a method that allows estim ation of lambda(c) from a point-source infiltration experiment.