System design including determination of lone spacing for proper overlap is based on manufacturers specifications. These specifications give discharge and wetted diameter pressure specifications for operating pressures at the gun. Many systems do not have functional pressure gages at the gun, instead, the operator relies on a pressure gage at the reel or in some cases at the pumping plant. The result is that many systems are not being operated at design specifications which results in improper overlap and poor application uniformity. System performance should be adjusted to design and manufacturers specifications. In some cases this will require decreasing the operation pressure which will result in less water loss to evaporation (lower pressure results in larger droplets which area less susceptible to evaporation and wind drift). But, in many cases the operating pressure will need to be increased, resulting in greater water losses. Thus, water savings are estimated to range from -5 (more water us) to +5.

The costs of this modification may range from as little as $25 to simply install a pressure gage on the gun to over $6,000 if the pump or pipe needs to be replaced to achieve higher operating pressures. There are no net water savings estimated for this practice. While total water savings from this practice may be small, water use efficiency will improve because operating the system at the proper pressure will result in better application uniformity.

Source: Evans, R.O., K.A. Harrison, J.E. Hook, C.V. Privette, W.I. Segars, W.B. Smith, D.L. Thomas, and A.W. Tyson. 1998. Irrigation conservation practices appropriate for the Southeastern United States. D.L. Thomas (ed.) Geologic Survey Project Report No. 32. Georgia Geologic Survey, Georgia Department Of Natural Resources, Environmental Protection Division, Atlanta, GA 30334. 43p.