HYDRAULICS OF CENTER-PIVOT LATERALS

Analytical equations that characterize hydraulics of center-pivot laterals with and without end-gun sprinklers were developed. The equations include computation of pressure-head distribution; pressure-head loss; and maximum, minimum, and average pressure heads and their corresponding locations of occurrence along a lateral. The proposed equations are important in design and evaluation of center-pivot irrigation systems since critical reference pressures can be easily determined and their corresponding locations can be readily identified in the field. The velocity-head term was included in the complete set of developed equations. A simplified solution that neglects the velocity-head term and uses the Darcy-Weisbach formula for computing friction loss in a typical center-pivot lateral with an end-gun sprinkler is also included. The results are in good agreement to those computed by a stepwise solution in a variety of test conditions. Discrepancies between results from these methods are within the accuracies of pressure gages normally used in irrigation evaluations. The proposed equations simplify important practical applications, such as system design and evaluation. Besides design, other potential applications of the proposed equations include analysis of energy consumption and uniformity of water application due to hydraulic behavior under different design and operating conditions.