Errors in Infiltration Calculations in Volume-Balance Models

Abstract

Volume-balance models of surface irrigation calculate the infiltrated volume at a given time as a product of the stream length, upstream infiltration, and shape factors. The best-known expression of this type was derived by combining the Lewis-Milne equation with empirical power-law expressions for infiltration and advance as functions of time. This expression results in systematic errors that are not well understood by users of volume-balance methods. This article examines those errors in furrow irrigation by comparison with infiltrated volumes computed with zero-inertia simulation. The potential for errors is greatest with light soils and where the bottom slope is large enough to produce kinematic flow conditions. An example is presented to show how these errors in a parameter-estimation problem based on a volume balance can be corrected iteratively with the help of zero-inertia simulation.