Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2009
Publication Date: 10/1/2009
Citation: Bautista, E., Clemmens, A.J., Strelkoff, T. 2009. Structured application of the two-point method for the estimation of infiltration paramaters in surface irrigation. Journal of Irrigation and Drainage Engineering. 135(5):566-578.
Interpretive Summary: Determining the infiltration properties of surface irrigated fields is one of the greatest challenges in surface irrigation engineering. Several procedures have been proposed to estimate those properties from field evaluation data. Among them, one of the best known procedures is the two-point method. Many of the assumptions on which the two-point method relies are often violated in the field due to the erratic nature of the data. Thus, the engineer has to be ready to adapt the estimation procedure, given the nature of the data, in order to make the best use of the available data. This study outlines a strategy for using the two-point method, based on modifications to the original concept, with the goal of improving the accuracy of the infiltration estimates. This information should be useful to field irrigation specialists, including NRCS personnel and extension agents, and to other surface irrigation researchers.
Technical Abstract: Elliott and Walker’s (1982) two-point method is one of the best known procedures for estimating empirical infiltration parameters from surface irrigation evaluation data. Success of the method is highly dependent on the quality and nature of the data because it uses very limited inputs. This article reviews alternatives for improving two-point method results based on data typically collected for the application of the method. Availability of post-advance data greatly enhances the accuracy of results. Improved surface storage estimates can help in cases where surface storage is large relative to the applied volume during advance; otherwise, the improved estimates will change the parameter values, but not the performance of the estimated function. Because of the erratic nature of the field data, the underlying mass balance equation may be difficult to satisfy at different times and, therefore, the estimated parameters can be very sensitive to the data, in particular the infiltration exponent. Given that many combinations of empirical parameters can nearly satisfy the mass balance equations, one can try to find an approximate solution by forcing one or more parameters to reasonable values. Highly erratic advance data can hinder the estimation process and for those cases, use of post-advance data may provide more reliable estimates.