RELIABILITY OF OPTIMIZED FURROW-INFILTRATION PARAMETERS

The reliability of furrow-infiltration parameters computed from advanc e measurements was analyzed. Lumped parameters were obtained using the least-squares approach. The objective function was formulated using a dvance time and velocity observations as a function of distance. Predi cted values were calculated with a finite difference hydrodynamic mode l with wetted perimeter-dependent infiltration. The Extended Kostiakov equation was used to describe infiltration-rate variation with time. Reliability was examined by comparing recorded total intake and runoff with values predicted with the single average parameters. Results sho wed that reliability of coefficients depends on the relationship betwe en infiltration variability, furrow length, and inflow rate. In partic ular, relatively short irrigation times hampered the identification of the steady infiltration rate. Spatial trends in infiltration rates af fected the reliability of parameters as well. The magnitude and nature of the resulting prediction errors was found to be dependent on the d irection of the trend relative to the flow direction. In general, velo cities appeared to provide better estimates of average infiltration ch aracteristics than advance times but weighted least squares may be req uired to compute the parameters from field data.