Characterizing microtopographical effects on level-basin irrigation performance

Microtopography has long been recognized as one of the key variables in level-basin irrigation performance, although little effort has been devoted to establish its relevance. In this work, experimental data are used to quantify the influence of microtopography on irrigation performance. An irrigation evaluation was performed on a small level-basin (256 m(2)) LASER levelled to zero slope. Irrigation depth was gravimetrically measured and estimated at the 49 nodes of a regular network. Data from the irrigation evaluation and a two-dimensional flat-bed model were used to estimate irrigation depth. Irrigation times, soil surface elevation and distance to the inlet were estimated at the same nodes, and a correlation matrix was computed. Results showed that soil surface elevation was highly and significantly correlated with the times of advance (0.725***), recession (-0.815***) and opportunity (-0.852***), and with the measured irrigation depth (-0.583***). Distribution uniformity using soil water measurements was 71.0%, Estimates from the irrigation evaluation and the two-dimensional model were 85.3% and 94.9%, respectively, The irrigation evaluation procedure could explain 30***% of the measured variability in irrigation depth. A large part of the unexplained variance in measured irrigation depth seems to be due to the spatial variation of infiltration properties. Predictions by the two-dimensional model were not significantly related to the measured values. A simple method was devised to estimate microtopography-adjusted irrigation performance from the results of a Aat bed model and the standard deviation of elevation. Microtopography can have an important effect on level-basin irrigation performance. Models not considering this variable may incur large errors when simulating irrigation performance.