APPLICATION OF GEOSTATISTICS TO CHARACTERIZE SPATIAL VARIABILITY OF INFILTRATION IN FURROW IRRIGATION

A FORTRAN IV programme, SAMINF was developed for calculating estimatio n variances when interpolating infiltration along a furrow by kriging from regularly spaced data and a previously determined semi-variogram of infiltration. The variances were calculated for a series of furrow section lengths, and for various spacings of point measurements. From the plot of the output of the programme, the sampling intensity requir ed to obtain a desired level of precision of infiltration was obtained . Another programme was written for interpolating the average value of infiltration for a section of a furrow. This was made a subroutine an d associated with a kinematic wave model for simulating furrow irrigat ion in which infiltration could vary spatially. The model was used to analyze the performance of irrigations under varying levels of estimat ion variance and the results compared to field data. Geostatistics was found to be a useful tool for characterizing infiltration in furrows. The effect of the level of precision in the estimation of infiltratio n on the performance parameters of the irrigation was most significant on the distribution uniformity. The level of precision in the measure ment of infiltration was found to be adequate when the standard error in the measurement of infiltration was about 30% of the geometric mean value.