Volume Balance Irrigation Advance Equation: Variation of Surface Shape Factor

Abstract

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. In this paper an accurate algebraic VB equation is developed to predict the advance phase in surface irrigation. In the suggested analysis the average surface water depth is considered to be variable in time. By systematic analysis of accurate kinematic-wave (KW) numerical solutions, the behavior of the surface profile shape factor used in the VB equation is examined. A new equation describing the time dependence of the surface shape factor is derived. Comparison tests indicated that the suggested variable surface shape factor VB equation produces essentially the same results as the KW numerical method. The suggested equation is improved for the case of level or low sloping borders.