Accounting for interference effects in furrow infiltration with moment analysis

Authors: Bautista, Eduardo; LAZAROVITCH, NAFTALI - Ben Gurion University Of Negev

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2023
Publication Date: 5/14/2024
Citation: Bautista, E., Lazarovitch, N. 2024. Accounting for interference effects in furrow infiltration with moment analysis. Journal of Irrigation and Drainage Engineering. 150(4). Article 04024012. https://doi.org/10.1061/JIDEDH.IRENG-10043.
DOI: https://doi.org/10.1061/JIDEDH.IRENG-10043

Interpretive Summary: Hydraulic studies of furrow irrigation systems typically model infiltration empirically, as a one-dimensional flow process, even though the actual flow is two-dimensional. Those studies assume that the water distributes uniformly across the furrow spacing and ignore the potential merging of neighboring water plumes, a process identified herein as interference. Interference reduces infiltration rates and, thus, compromises the accuracy of furrow irrigation studies. Use of the two-dimensional porous media flow equations is desirable for modeling infiltration interference in furrow irrigation but such an approach is computationally expensive and prone to numerical incidents. A simulation study was conducted to identify conditions under which furrow interference can develop, to quantify its impact on infiltration rates, and to develop an approximate modeling approach. A statistical technique, moment analysis, was used to quantify the horizontal expansion of the water plumes. Statistics were developed for unconstrained and constrained plumes for different flow geometry configurations and soil factors. Interference is less likely to be experienced under typical irrigation condition in soils with relatively high sand contents, and the impact on infiltration rates can be expected to be small. Interference is more likely in soils with high silt content and, under the range of conditions studied, can reduce infiltration rates by 30 percent or more. For any given set of flow geometry and soil conditions, interference effects can be predicted from the potential expansion of an unimpeded plume relative to the ultimate lateral expansion of the constrained plume. This concept was used to modify an existing semi-physical furrow infiltration model. The model produces reasonably accurate infiltration predictions in comparison with solutions of the two-dimensional equations of porous-media flow. Hence, it is of value for practical irrigation studies. The approach will be added to the WinSRFR software package developed by ARS. This information is of interest to users and developers of surface irrigation models, and to researchers of infiltration processes.

Technical Abstract: The problem of interference in furrow infiltration was examined. Interference results from the merging of the wetting plumes of neighboring furrows and reduces infiltration rates. The goal was to modify to an existing semi-physical model of furrow infiltration to account for interference effects. Moment analysis was used to characterize the transverse spread, measured in standard deviation units, of a constrained furrow infiltration plume relative to an unconstrained one. For any combination of furrow spacing, boundary conditions, initial conditions, and/or soil hydraulic properties, the ultimate value of the standard deviation in the horizontal direction of a constrained plume is given by the furrow semi-width divided by the constant 1.7. This constant can be related to an ellipse of infiltrated water for an unconstrained water plume, computed under the same initial and upper boundary conditions, of the same width as the furrow spacing of the constrained plume. The onset of interference can be predicted from this relationship and the reduction in infiltration rate can be quantified from the growth of the wetting plume of the unfettered plume relative to the constrained one as a function of infiltration volume per unit length. These concepts were used to modify the lateral flow component of the existing semi-physical furrow infiltration model. The modified model predicts infiltration with reasonable accuracy in comparison with solutions computed with the two-dimensional Richards equation.