Engenharia de Sistemas de Irrigação e Drenagem

Friction Head Loss in Center-Pivot Laterals with the Lateral Divided into Several Reaches

Abstract

Manuel A. Tabuada

This paper presents efficient closed form expressions, based on the discrete outflow distribution, to compute the friction head loss and the friction correction factor in center-pivot laterals divided into several reaches. Since such formulas cannot be found in the literature, we develop these expressions based on the discharge required by each sprinkler and each reach to irrigate an annular area.

These expressions can be used in center-pivot laterals with and without end gun sprinkler and with and without closed outlets at the beginning of the lateral. Moreover, these expressions also allow to compute the head loss between the last outlet and the end gun sprinkler usually neglected by another investigators.

These expressions were developed for center-pivot laterals with: 1) a single diameter and with constant spacing between sprinklers along the lateral and 2) a single diameter and a lateral divided into several reaches where the spacing between outlets is constant but the spacing is different in each reach.

This apparently complex method is easy to implement computationally and easy to understand. It can be applied using the Hazen-Williams, Scobey or Darcy-Weisbach friction loss equations.

An application using the Hazen-Williams equation to compute the friction head loss for a center-pivot divided into three reaches is presented. The results obtained with the method of the discrete outflow distribution are compared with the method of the continuous outflow distribution.