The principal objective of evaluating surface irrigation systems is to identify management practices and system configurations that can be feasibly and effectively implemented to improve the irrigation efficiency. An evaluation may show that higher efficiencies are possible by reducing the duration of the inflow to an interval required to apply the depth that would refill the root zone soil moisture deficit. The evaluation may also show opportunities for improving performance through changes in the field size and topography. Evaluations are useful in a number of analyses and operations, particularly those that are essential to improve management and control. Evaluation data can be collected periodically from the system to refine management practices and identify the changes in the field that occur over the irrigation season or from year to year. The surface irrigation system is a complex and dynamic hydrologic system and, thus, the evaluation processes are important to optimize the use of water resources in this system. A summary of the data arising from a field evaluation is enumerated below.
There are several publications describing the equipment and procedures for evaluating surface irrigation systems, but not all give a very correct methodology for interpreting the data once collected. The data analysis depends somewhat on the data collected and the information to be derived. This section will deal with two aspects of an evaluation. The first is the definition of the typical field infiltration relationship using the evaluation data describing the surface flow. The mathematical basis of the infiltration analysis will be the extended form of the Kostiakov-Lewis formula (Eq. 15). The second is the evaluation of the efficiency of the irrigation event studied. Although many performance measures have been suggested, only four will be noted herein: (1) application efficiency; (2) storage efficiency; (3) deep percolation ratio; and (4) runoff ratio. These will be defined here before detailing the analyses of infiltration and performance.