The proper size and diameter of the lateral sprinkler pipe is associated with the variations of pressure head along the pipeline; the greatest pressure head variations, the smallest pipe size and thereby an increase in the required pressure head at the inlet of lateral pipe and the pumping power unit. The pattern of water distribution of sprinklers operating with different operating pressure will accordingly varies and may leads to variations in uniformity of water application along the lateral pipe. The research purpose is to study the effect of pressure head variation on the uniformity of the water distribution along the lateral pipe by adopting different values of the friction head losses that expressed as a fraction of average operating head, and linking with spacing between sprinkler heads. Furthermore, this study aims to compare between the increase in pumping power cost to ensure operating head at the lateral inlet associated with increase in the fraction of friction head losses, and decrease in the cost of the pipe. 18 tests were carried out to obtain the water distribution pattern for single sprinkler under different pressure heads and for five different type sprinklers,the water distribution pattern of a single sprinkler was estimated as a function of distance from the sprinkler and the pressure head with non-physical formulas and high determination coefficients. Fractions of head losses due to friction were chosen to be (10, 20, 30, 40, and 50) % of the sprinkler operating head. A computer program was developed to compute the pressure head at each sprinkle, water distribution pattern, and water application uniformity of the sprinkler network system using different sprinkler head spacing and three levels of operating heads. Also, the economics of pipe size and pumping operation cost using the selected fractions of the friction head losses was studied.
The results show that the water distribution uniformity increases when the pressure head at sprinkler head increases and this increase varies according to the sprinkler type and spacing; there is no observable change between the system water distribution uniformity and uniformity coefficient of application at the average operating pressure head for all sprinkler spacings and friction head looses fractions except the case of friction head loose equal to 50% of the operating head that showed very small differences. Also, the annual pumping cost to ensure required pressure head at lateral pipe inlet using same average operation head is constant for all used sprinkles. The total annual cost increases when the adopted friction head loose in the design of lateral sprinkler pipe increases stating that the economic pipe size is associated with low friction.