Design of Nonzero Uniformly Sloping Laterals in Trickle Irrigation Systems

Abstract

An analytical method was developed to design evenly sloping, pressurized, nontapered, multiple-outlet pipes. Assuming spatiotemporal continuity of emitter flow rates, the approach was derived from the solution of analytical nonlinear differential equations. A straightforward relationship was established between the inlet discharge, the lateral slope, the diameter, and the pressure head at the upstream and downstream ends. Five pressure head grade line profiles were derived: uniformly uphill, level ground, steeply downhill, moderately downhill, and slightly downhill. For moderately downhill laterals, the theoretical analysis revealed that the pressure head at the outermost rim was independent of the inlet discharge. For the other profiles, the pressure head at the downstream edge was parameterized as a function of the inlet discharge. The iterative computation of the inlet discharge is a prerequisite for the inference of the other design parameters. This approach was successfully compared with the stepwise method that is deemed to be the most accurate.