Flexible Irrigation Systems: Concept, Design and Application

This paper presents the need, value, and concept of flexible irrigation water supply systems that can deliver water with flexibility in frequency, rate, and duration under the control of the farmer at the point of application using a limited rate arranged-demand or other schedule. It introduces the needed terminology including "congestion"-how much reserve time and capacity is required to assure water delivery at the frequency and rate desired. An illustrative design procedure for the necessary pipeline and reservoir capacities is illustrated. The techniques discussed emphasize the conversion of the economical steady supply canal flows to flexible on-farm usage through the use of service area reservoirs located between the secondary and tertiary systems, and of semiclosed pipelines and/or level-top canals as automated distribution systems which facilitates the farmers' need for daytime only variable on-farm deliveries to permit optimization of on-farm water management. This improved management is the ultimate source of increased food production after improved crop, land, and water resources have reached their maximum. The coordinated use of return flow systems is described. fective and responsible management of water resources is critical. 24 h. These restraints have no correlation with soil intake rate or Introduction In areas where irrigation is essential for crop production, the ef­ The on-farm problems created by the use of a rigid rotation schedule that permits a canal to operate continuously at a constant flow rate (an engineer's dream but a farmer's nightmare) are beginning to be acknowledged in planning. The rigid rotation supply forces wasteful water use such as improper timing, over irrigation and runoff, prevents effective use of rainfall, requires inconvenient and excessive labor, creates conflicts over water, and inhibits good farm management. It may be associated with sub­ surface drainage, high water table caused salinity, and reduced production problems. A flexible irrigation supply permits a farmer to manage his land, water, weather, and labor resources as one integrated unit within his total farming program. Flexibility is essential to opti­ mizing farming operations and maintaining sustainable irrigated agriculture. The value to widely utilized surface irrigation meth­ ods of large variable flow rates and daytime only sets, and half or less as much labor conveniently and more effectively used, must be considered in the economics of projects (Merriam and Free­