Automatic Cutback Furrow Irrigation System Design

A field method for determining the size of a constantly decreasing furrow irrigation stream just adequate to prevent runoff after an initial stream has advanced the length of the furrow is described. This reduced stream can be approximated by several streams of constant flow, each applied for equal times. Use of the constant streams makes the irrigation system amenable to automatic methods of water application. Assuming that stream size is to be varied by regulating head-on spiles set in the walls of the irrigation lateral, procedures for determining spile size, variation in elevation of adjacent banks of spiles, and heads on the spiles for each discharge are presented. Equations are given for the number of furrows to be irrigated from each bay of the lateral with a given water supply. Methods for determining times of application and volumes of water supplied by the initial stream and each of the reduced streams are given. An example illustrates the application of all procedures and equations.