Developing a new design procedure for microirrigation laterals with unequal emitter spacings and/or unequal emitter discharge rates to allow for site -specific irrigation management.

摘要

Traditional microirrigation design procedures offer little capability for site-specific irrigation management. Such procedures are based on the fundamentals of uniform plant water requirements and spacings and have always focused on achieving high emission uniformity. Therefore, there is a need to develop a new design procedure for laterals with unequal emitter discharge rates to match variable plant water requirements, and unequal emitter spacings to match the need for unequal plant spacings. A comprehensive study was conducted to develop a new design procedure for such laterals. The methodology followed in this study consisted of four phases. In phase one, a step-by-step (SBS) model was built to simulate the effects of study variables on lateral hydraulics. In phase two, field experiments were conducted to verify the SBS model. The percentage difference between theoretical and experimental results was satisfactory and ranged between ±6.0%. This indicated that the SBS model is a reliable tool in simulating the effects of study variables on lateral hydraulics and led the way for developing a simplified technique to calculate head loss in laterals. In the third phase, the segment-based analysis (SBA) technique was developed to simplify the procedure of calculating head loss in laterals with unequal emitter spacings and unequal emitter discharge rates. The SBA technique transforms the lateral into a virtual lateral divided into a certain number of equal-length segments and replaces existing emitters in each segment by one virtual emitter positioned at the center of that segment. The accuracy of the SBA technique was found to be a function of the number of segments used. Higher accuracy was achieved as the number of segments was increased. ±5.0% accuracy levels were attained by using five segments, which proved that the SBA technique is a reliable alternative to the lengthy SBS procedure for computing lateral head loss. Finally, a new lateral design procedure was developed and presented in mathematical and graphical formats. With the use of a hand-held calculator, both formats of the new design procedure can be utilized in the field. In conclusion, the new lateral design procedure is characterized by acceptable levels of accuracy and simplicity.