Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2012
Publication Date: 8/1/2012
Citation: Bautista, E., Strelkoff, T., Clemmens, A.J. 2012. Improved surface volume estimates for surface irrigation balance calculations. Journal of Irrigation and Drainage Engineering. 138:715-726.
Interpretive Summary: Surface irrigation models based on volume balance are part of the toolbox used by engineers to analyze irrigation systems. Volume balance models require substantially less computational effort than models that account for the unsteadiness of the flow, but they are also less accurate. They are particularly useful for analyses that would require running an unsteady simulation model repeatedly. Volume balance calculations are extensively used by WinSRFR, a surface irrigation software package developed by ARS. The accuracy of volume balance models depends largely on the engineer’s ability to accurately estimate the volume of water stored above the soil surface during an irrigation event. Those estimates are developed based on assumptions that often are not met in practice. This study reviews the procedures available for estimating the surface storage volume, examines how irrigation system characteristics affect our ability to develop those estimates, and proposes improvements to existing computational procedures. The results are of interest to irrigation specialists, including NRCS personnel, irrigation consultants, and researchers.
Technical Abstract: Volume balance calculations used in surface irrigation engineering analysis require estimates of surface storage. Typically, these calculations use the Manning formula and normal depth assumption to calculate upstream flow depth (and thus flow area), and a constant shape factor to describe the relationship between upstream and average flow area. Improved computational procedures for surface storage have been implemented in analytical procedures based on volume balance calculations in WinSRFR, a software package for the hydraulic analysis of surface irrigation systems. However, those procedures can still result in inaccurate surface volume determinations under a variety of hydraulic conditions. This article reviews alternatives for the computation of upstream depth and surface shape factor in volume balance calculations, examines how hydraulic conditions affect the evolution of the surface profile and, thus, our ability to accurately estimate surface volume, and suggests improvements to the procedures currently implemented in the WinSRFR package.