Accounting for Interference Effects in Furrow Infiltration with Moment Analysis

Furrow infiltration interference results from the merging of the wetting plumes of neighboring furrows and reduces infiltration rates. Simulation models and computational procedures used to analyze furrow irrigation flows currently ignore this effect. An understanding of this process and its impact on infiltration is needed, and infiltration modeling approaches must be modified to account for interference effects, if those effects are substantial. A simulation study was conducted to characterize the transverse spread of furrow infiltration plumes subject to interference (i.e., constrained plumes) relative to unconstrained ones and its impact on infiltration rates. Constrained and unconstrained plumes were computed for the same furrow geometry, soil hydraulic properties, initial conditions, and boundary conditions and different combinations of these variables were tested. A relatively wide computational domain was used to compute the unconstrained plumes, whereas a relative narrow domain was used for the constrained plumes. Moment analysis was used to evaluate spread and fraction of infiltrated water contained within elliptical different regions of the plume. For any set of conditions, when a plume ceases to expand horizontally, its final horizontal standard deviation is approximately equal to the semiwidth of the constraining furrow divided by 1.7. This constant, and the resulting standard deviation, define an ellipse of an unconstrained infiltration plume that, at some point in time, matches the width of the constraining furrow. The onset of interference, and the resulting decrease in infiltration rate, can be predicted from the evolution of the standard deviation of the unfettered plume relative to the ultimate standard deviation of the constrained plume. These concepts were used to modify the lateral flow component of an existing semiphysical furrow infiltration model. The modified model predicts infiltration with reasonable accuracy in comparison with solutions computed with the two-dimensional Richards equation. Results suggest conditions under which interference is likely.