An analytical approach to predict the moistened bulb volume beneath a surface point source

An analytical approach for predicting the wetted soil volume underneath an emitter laid on the ground surface is developed. The approach is based on: (1) the Green and Ampt assumption, (2) Hammami et al. model that enables the inference of the wetted soil depth from the radius of the humid area at the ground surface and (3) the hypothesis that the bulb keeps a semi-elliptical shape whose diagonals are merged with the soil surface and the symmetry axis, respectively. Knowing the initial water content θi, the soil hydraulic conductivity Kf and the water content θf at wetting front position, the proposed approach allows the inference of the wetted bulb volume from the radius of the wetted spot at the soil surface. Experimental trials were carried out in laboratory conditions to assess the relevance of the proposed method. The measurements were made during the infiltration process in three soil types: loamy clay, sandy clay loam and sandy clay. The wetting front progression was monitored via the measurement of the wetting front radius Rf(t) at the soil surface and the determination of the moistened bulb volume Vb(t) by water balance equation. The Vb(t) values thus determined were compared to those predicted by the present approach. The results exhibit a good agreement between calculated and predicted data. Furthermore, predicted values are close to those inferred from Healy and Warrick (1988) model.