The planning and design of an irrigation system is an engineering problem which can be solved by numerical methods, i.e. with the aid of computer software. The software should relieve the engineer of the arduous task of interpreting tables, referring to charts and maps and performing complicated calculations. Software can complete this task quickly and can easily calculate a number of what-if cases. The engineer has to set-up or acquire the basic input (such as equipment lists and soil attributes) and then carefully balance the variables so that an optimal solution can be obtained in less time than was possible in the past.

**Introduction **

Data to be assembled for the planning of an irrigation system includes the type of crop (transpiration and evaporation), the climate (humidity, temperature and radiation) and soil (water holding capacity). In order to distribute water to the crop you need an irrigation system which includes pipe networks, pumps and emitters. A pipe network is constructed of pipe lengths (sections) with nodes (junctions or valves) and emitters.

Designing an effective large scale irrigation systems can be a time-consuming procedure. Manual calculations can lead to ambiguous or faulty results. Small changes can lead to a complete recalculation. The ideal solution is the use of a computer program to do the calculations. In order to find a cost effective solution a computer model of the network has to be constructed, constraints to be defined and a linear programming algorithm applied.

**Software**

Numerous irrigation design programs have been developed enabling the engineer to produce a more precise and effective pipe network plan and to complete the design work in less time than was previously possible. Most programs developed so far provided at best partial solutions related to specific engineering design calculations and could not formulate a comprehensive, fully computerised irrigation design integrating all project parameters. These programs, though more advanced than previous design techniques, were cumbersome, since each program dealt with a specific problem in isolation without any means of linking programs and procedures. Consequently, a change in any variable at a critical stage of design necessitated almost complete redesign of the entire system.

There are many reasons for the lack of a complete, integrated design program; the two main ones being the many variables involved in irrigation design and their multi-disciplinary nature. The computations involved required a powerful computer. The availability of cheap and fast microcomputers makes it possible, as well as economically feasible, to put the microcomputer on the design engineer’s desk and to combine all the phases of irrigation project design – from general planning to system management.

With WCADI you can build up and store many projects and cases, with the possibility of duplicating parts of the data. Data such as the equipment file can be built up from scratch or can be imported if the supplier makes it available. This data is logically grouped into tables so that global groups of equipment can be defined, as well as all the necessary details about pipe diameters, emitters, etc.