System Design Criteria Objectives:
• You will learn that designing an irrigation system means satisfying three criteria - water availability, irrigation system capacity and distribution uniformity.
• You will understand that a design is limited by operating time and water supply.
• You will learn that application uniformity is subject to keeping pressure losses low.
When building, modifying, maintaining, or operating any part of an irrigation system, one must always consider the effect of that part on the entire system. The original design must be kept in mind and the balance of flows and pressures must be maintained.
An irrigation system should not be required to operate 24 hours a day to meet crop needs; some maintenance downtime should be included in the daily schedule. This extra capacity may be needed for extreme weather conditions.
Pressure losses in the piping system, emitter or sprinkler variability, and variability in plant water demand all contribute to the non-uniformity. Uniformity can be improved by investing in more expensive irrigation equipment, such as larger diameter pipes and more sprinklers to achieve better overlap of watering patterns. This investment may not be justified by the slightly better uniformity. However, the more uniform the irrigation system, the less over-irrigation is required.