In a drip irrigation system, a major design criteria is a minimization of the discharge (or emitter flow) variation along a drip irrigation line, either a lateral or a submain. The discharge variation can be kept within acceptable limits in laterals or submains of a fixed diameter by designing a proper length for a given operating pressure. The discharge (or emitter flow) variation is controlled by the pressure variation along the

line which results from the combined effect of friction drop and line slopes. When the kinetic energy is considered to be small and neglected in a drip irrigation line, the pressure variation will be simply a linear combination of the friction drop and energy gain or loss due to slopes as suggested by Wu and Gitlin [6] and Howell and Hiler [2].