Multicriterion approach to the evaluation of irrigation systems performance
In recent years the importance and the lack of comprehensive methodologies for measuring the performance of existing irrigation schemes has been widely expressed. The objective of this study is to develop a systematic procedure by which some use can be made of the large quantities of data, already routinely collected in irrigation schemes, for the purpose of their regular seasonal evaluation. Consideration is confined to the performance of the main irrigation system of small-holder, canal-fed irrigation schemes of the developing countries. A generalized conceptual framework has been developed for a methodology by which the performance criteria for any irrigation system can be identified and combined together into a single index which measures the overall performance of the system. Six criteria have been identified as adequate for characterizing the important features of the performance of any irrigation system. These are; adequacy, equity, water losses, water user convenience, cost and durability. New methods for characterizing each of adequacy, equity and water user convenience have been developed and tested using data from the Gezira scheme, Sudan. Characterization of adequacy, equity and water losses involves the development of a soil moisture simulation model and characterization of the water user convenience involves the use of the concept of the fuzzy set theory. Identification of the criteria to be used in evaluating any particular system(s) and evaluating the trade-offs between them requires the participation of the decision-maker in the system(s) to be evaluated. This is achieved through the use of the multi-attribute utility theory. It has been applied with a group of Sudanese officials in order to derive their utility functions. The utility function reflects the decision-maker's strength of preferences over different achievement levels of each objective and his trade-offs between different objectives. The derived utility functions are reported and their usefulness is discussed. The methodology developed provides a useful tool for measuring the performance of irrigation systems, comparing the performance of different systems and assessing improvement in performance resulting from rehabilitation investments.