Existing Problem: 23 degree Impact Sprinklers on Top of Boom

High Angle Impact Sprinklers High angle impact sprinklers may have two problems that reduce application efficiency -- the operating pressure is typically in the high range (>80 psi) and the angle of spray throws the water high into the air. With high pressure nozzles many of the water droplets are small leading to wind drift, direct evaporation of droplets into air, and loss of water from droplets during settling. With high throw angles, droplets spend more time in the air and thus have more time for those water losses from droplets.

In their favor many of the high pressure, high angle sprinklers spread the water far enough during throws that instantaneous application over a spot on the soil will be lower than infiltration. All applied water, that does not evaporate or drift, will enter the soil.

BMP's suggested below reduce the throw angle and/or the operating pressure.

Water Conserving Practice: Place Reduced Angle Sprinklers on Top of Boom
This package should include new sprinkler spacing and operation at a lower pressure. Reduced angle sprinklers have larger droplets, and with lower trajectory, they are less likely to be carried off by wind. Caution is needed to prevent runoff water losses (see below).

¹Potential No. of Irrigation Systems Affected	850
Estimated Water Savings (%)	10 (5 to 15)
²Average Year Water Savings (million gal.)	1616
³Dry Year Water Savings (million gal.)	2770
Est. Cost of Full Implementation on Avg. System ($, 1998)	$1200
Statewide Costs for Full Implementation ($, 1998)	$1,020,000
Cost / Unit of Water Saved in Average Year ($, 1998 / million gal.)	$631

Estimated water savings are between 5 and 15 percent. The low end saving is associated with systems which primarily operate at night using good practices. The high end is associated with systems which operate continuously through 24 hours in very open areas. The average estimated water savings is about 10%

Of the 8,000+ center pivot systems currently in the state of Georgia, 850 are estimated to be candidates for this type improvement. All systems with 23 degree impact sprinklers on top of the pivot are not candidates for the change due to the limitation on soil intake rates. This is also the sprinkler package recommended for wastewater application so those systems will remain 23 degree impact sprinklers. The potential water savings from this practice alone would be about 1,616 million gallons during an average year. The cost to implement such a change will range from $500 to $2,000 per system depending on the amount of labor required. The estimated statewide cost for full implementation is $1.02 million (using a $1,200 average). The cost per unit water saved is estimated to be about $631 per million gallons of water saved.

The reduced angle impact sprinklers will apply more water per unit area than the impact sprinklers at a higher pressure. If the soil is not capable of handling the higher application rate, irrigation water would run off and be ineffective. As with all sprinkler packages, caution must be taken so that the instantaneous application rates remain below the minimum soil infiltration rate along the length of the pivot, especially nearest the end towers where higher ground speed forces the application rates to increase in order to maintain the same total application along the entire length of the pivot. Alternatively runoff can be minimized through enhanced infiltration of conservation tillage or temporary ponding in furrow dikes.

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.