The area to be irrigated is divided into sub-areas and each sub-area can be divided into blocks. A sub-area of the area is planted with one particular crop, and has the same crop layout, i.e. identical plant and row spacings and field irrigation system. A sub-area may be divided into a number of blocks for agrotechnical or irrigation purposes. The software designs the irrigation system of a block according to the parameters and data the user inputs. Certain information must be entered in the graphical environment, other information can be entered in the text environment, i.e. updating tables directly. Inputting data in the graphical environment implies that the graphical input is digitised and written to tables as well.
The discharge rates from the emitters in a lateral depend on the distance from the valve (due to pipe friction) and the profile, i.e. the slope (due to gravity). The ideal solution is equal discharge rates from all the emitters but the practical solution is discharge rates varying within a band of pressure.
Figure 5-1: Lateral or sub-main pressure curves, profiles and pressure tolerance (band)
An easy solution would be to use a large pipe size with little friction, so as to obtain an even pressure (even flows from the emitters), but this would not take into account the effect of any slopes, and the third factor is that the cost of the pipe increases with the diameter (expensive solution). The total optimised solution is a set of varying diameter pipes in the lateral that will deliver discharge rates within an allowable band of pressures (emitters flow) for the lowest cost of the set of pipes.
WCADI’s method calculates the optimal set of pipes by first calculating the sets of pressure curves for the various diameters of the pipes, taking into consideration the slope(s). It connects the various individual curves so that the combination curve, for a set of connected pipes with varying diameters, stays within the band of pressures and, at the same time, connect in such a way that the total cost is minimized.
There are 10 functions under the text environment, i.e. the Block design submenu. Some of the functions supply summaries of the required pipe materials, costs and system pressures.
1 SUB-AREA DATA
2 DESIGN PARAMETERS
3 MAXIMUM LENGTH CALCULATOR
4 BLOCK LAYOUT
5 DESIGN – POLYPLOT
6 DESIGN – MANUAL
8 TECHNICAL SUMMARY
9 DESIGN SUMMARY
10 SUB-MAIN EQUIPMENT
11 ADDITIONAL GRAPHICAL SUBJECTS FOR BLOCK DESIGN
These functions are complemented by functions in the graphical environment.