|Hunsaker, Douglas - Doug|
Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2010
Publication Date: 5/10/2011
Citation: Perea, H., Bautista, E., Hunsaker, D.J., Strelkoff, T., Williams, C.F., Adamsen, F.J. 2011. Nonuniform and unsteady solute transport in furrow irrigation II. Description of field experiments and calibration of infiltration and roughness coefficients. Journal of Irrigation and Drainage Engineering. 137(5):315-326. Interpretive Summary: Fertigation, the application of fertilizer with irrigation water, is widely practiced in the Western United States. In surface irrigation systems, fertigation typically generates fertilizer offsite discharges that have the potential of contaminating ground and surface water resources. Modeling tools can help predict the fate of fertilizer applied with the irrigation water and can contribute to the development of practices and technologies that will reduce or eliminate the risk of offsite fertilizer discharges. This work documents a study that was conducted to calibrate a proposed fertigation model and the process used to calibrate the model’s parameters. Results illustrate the capabilities of the proposed model but also the limitations of the calibration procedures. The study should be of interest to researchers, extension agents, and consultants interested in water-contaminant transport problems.
Technical Abstract: Field tests were conducted to obtain irrigation evaluation and solute transport data that were used to calibrate and validate an advection-dispersion model for furrow irrigation. Empirical infiltration equation and roughness parameters were estimated from the field data. These estimates were used as inputs to a hydraulic simulation model. The hydraulic model calculated the variation in velocity with time and distance along the furrow, which are required by the advection-dispersion model. The inflow rate was measured with a totalizer meter and a flume and resulted in different measured average inflow rates. The difference in the average inflow was small for the first furrow fertigation test reported herein, but large for the second. Overall, the hydraulic and solute transport model predictions matched the observations with reasonable accuracy, better for the first test than for the second. Hydraulic simulation results proved nearly as accurate with infiltration function estimates derived from the meter or flume data, despite the difference in measured flow rate. Hence, the estimated infiltration function compensates for mass balance errors and provides limited clues about possible problems with the input data. The choice of infiltration equation used to fit the data (Branch vs. Modified Kostiakiov) had a greater impact on the accuracy of the hydraulic modeling results, but neither infiltration equation modeled all aspects of the irrigation event with superior accuracy. The timing and spread of the solute concentration pulses was well predicted, independently of the inflow data and infiltration equation used to fit the data. However, inflow rate differences between the meter and flume data clearly manifested themselves as errors in the predicted peak solute concentrations relative to the observations. Results show that accurate inflow and volume measurements are essential for accurate parameter estimation.