Surface Irrigation Advance Equation: Variation of Subsurface Shape Factor

Abstract

The volume balance (VB) algebraic equations based on the power advance assumption (i.e., the time invariance of the subsurface shape factor) may deviate significantly from accurate VB numerical solutions. By systematic analysis of the accurate VB numerical solutions obtained using the Kostiakov infiltration formula, the behavior of the subsurface shape factor as a function of time is examined. A new equation describing the time variation of the subsurface factor is derived. Using dimensionless analysis the new VB algebraic equation is demonstrated over the practical range of variation of surface irrigation parameters. The validation of the new VB equation is extended to infiltration formulas of any mathematical form. Comparison tests indicate that the suggested VB equation is more accurate than previous equations that assume time invariance of the subsurface factor.