Development Of A Computer Model For Pressure Losses In Trickle Irrigation Lateral Design

Abstract

This report deals with friction and minor losses in polyethylene (PE) pipe associated with trickle irrigation lateral design. Validity of the roughness coefficient in the Hazen-Williams equation for friction loss was questioned. The commonly accepted value of 140 for all flow rates was proved to be inaccurate for lateral design. My research showed that the C factor changed with flow rate and the value of 140 was much too high for low flow rates. An average value of 130 was recommended for flows common in trickle irrigation laterals. Also, that pressure losses across emitters are important was apparent in my experiments. Usual practice is to ignore these losses, but in cases where many emitters are used, the losses must be accounted for. A value of 1 was suggested as the emitter coefficient (K value) for the minor loss equation. A computer program was written to model a trickle irrigation lateral. This made it possible to compare different designs of the same lateral. It showed the effect of including minor losses in a lateral design. It also showed the effects of changing the C values in the Hazen-Williams equation when predicting friction losses along a lateral. The program is to help trickle irrigation designers by providing fast and accurate designs. Given a specific input, the program can give a designer the exact pressure needed at the head end of a lateral. It can also give him the length limit of a lateral and the emitter flow rates along the lateral.