Energy Grade Line Assessment for Tapered Microirrigation Laterals

Abstract

In pressurized irrigation systems the total long-term costs can often be minimized by dividing the pipeline into segments of different diameters. To properly design such a system requires an accurate hydraulic analysis. In this study, an analytical procedure was developed to simulate the energy grade line along trickle laterals with dual pipe sizes. Appropriate equations were developed to accurately estimate several important design factors such as the total head loss (JTot), the total required head at the inlet (Ein) and the minimum pressure head along the lateral (Emin). The methodology takes into account the effect of the number of outlets along each reach of the lateral, outflow nonuniformity, friction factor variation, velocity head changes, and local losses. Friction losses were evaluated using the power form equation of the Darcy-Weisbach formula. Local losses and velocity head change were both addressed by obtaining an average along the lateral constant coefficient which is a function of the number of outlets and the outflow at the downstream end of each reach. Two power functions were also used to estimate the outflow nonuniformity along each segment of the lateral. The accuracy of the proposed method is very high in all cases examined and the results tend to accurately follow the numerical stepwise solution. Assuming a uniform outflow for the proposed method results in accurate estimations of Ein and Emin but generally not of JTot. The nonuniform outflow approach, on the other hand, calculates all three design parameters with a high degree of accuracy.