Surface irrigation is used more than pressurized irrigation due to low cost, more efficient energy requirements, and better aeration of the root zone. The design, evaluation and simulation of surface irrigation systems rely on a knowledge of the movement of the water over the field. However, hydraulics of surface irrigation flow is more complicated flow than the other open channel flow due to the shallowness and unsteadiness of water depth and existence of permeable bed. In application of the volume balance (VB) models, it is generally assumed that the average depth of surface water is constant. This basic assumption may cause significant errors in computing advance water. In this paper, a model is developed for computing the advance distance and/or time of propagation for both border and furrow irrigation. Where, the surface and subsurface flow profiles in the advance phase are assumed to be of parabolic shape and their coefficients are determined by conditions in the gradually varied flow region, rather than in the rapidly varied flow region near the advance front. The model is applied for both border and furrow irrigation. The results are satisfied via testing with the field data obtained from different regions and various soil types and situation of field surface.