Equivalent friction factor method for hydraulic calculation in irrigation laterals

Abstract

A simplified method for the resolution of lateral hydraulic problems in laminar and turbulent flow is presented. At a first stage, the head losses are calculated applying the Darcy-Weisbach equation with a discrete and constant outflow model, which leads to a correction parameter equivalent to Anwar´s factor Ga. The difficulty arisen from the variation of the friction factor along the lateral (due to the discharged flow) is overcome by means of an equivalent friction factor (feqN). At a second stage, this head-loss model is used together with a variable discharge model based on Taylor polynomials to make a better estimation of the flow rate distribution by means of a successive-approximations scheme. This new approach directly allows the computation of the real mean lateral’s outflow and the minimum and maximum discharges. At a third stage, the previous results can be improved (if it is desired) by taking into account the nonconstant outflow distribution model developed in the previous stage. The proposed method is useful to workout the hydraulic computation of laterals with the inlet segment at full or fractional outlet spacing, and complex laterals when a different pipeline diameter, slope, flow regime or emitter gap have to be considered. Results are comparable to those obtained in the literature.