Under a trickle source, the flow of water in unsaturated soil takes place from a disc source having a radius changing with time due to change in the rate of infiltration. To predict the wetting pattern below an emitter placed on the soil surface, an unsteady, non-linearised numerical model has been developed in an oblate spheroidal coordinate system. Using this coordinate system, the problem involving disc source geometry having radius changing with time, is simplified, as the disc is a degenerate case of an oblate spheroid. The results of the proposed model are in close agreement with the experimental results of [Taghavi, S.A., Marino, M.A., Rolston, E., 1984. Infiltration from a trickle irrigation source. J. Irrig. Drain. Eng. ASCE 110 (4), 331-341] and the numerical model of [Bresler, E., 1978. Analysis of trickle irrigation with application to design problems. Irrig. Sci. 1, 3-17] developed in cylindrical coordinates. The applicability of the model has been analysed for special conditions of trickle irrigation e.g. large time water application, redistribution of soil water after discharge is cut off or reduced, and basin irrigation with restriction of surface water flow.
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