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This guide is intended to serve the needs of the irrigation technician for the evaluation of surface irrigation systems. The scope is focussed at the farm level. A limited series of graphical and tabular aids is given to relieve the user of some burden of computation. Unfortunately, the number of variables associated with surface irrigation prevents this from being completely practical. There are also two matters of philosophical nature that have led to the approach presented herein. First, the irrigation technician and engineer must understand the fundamental interactions characterizing surface flow in order to evaluate, improve, design and manage effectively. This suggests a mathematical presentation which briefly and concisely portrays these interrelationships. This guide omits nearly all theoretical development and presents the most basic mathematical description. Nevertheless, the complexity of the problem still requires an extensive mathematical analysis, even at this basic level. The expertise required of the technician is that of at least a secondary education and the engineer whose training needs to be at approximately the BSc level. The second philosophical aspect is the belief that irrigation engineering practices are moving steadily toward a computerized methodology. The interactions referred to above require large enough computational commitments that they are only feasibly evaluated with hand-held programmable calculators or microcomputers. As a result, the procedures outlined herein have been presented so they can be applied directly via computer. A diskette copy of this program source and executable codes for IBM PC and compatible microcomputers is available from FAO.

Some of the material used to develop this paper is included in more theoretical texts of the writer's. Occasionally, direct quotes and figures have been extracted without citation in order to minimize the diversions encountered by the reader. When the work of others has been used, more careful attention to the detail of the citation has been given. Surface irrigation is a complex subject which many have investigated and written about. The purpose of this guide was not to review the technical literature exhaustively and many valuable works are not cited, but it is hoped that the essence of surface irrigation evaluation and design practice has been captured.

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