Sprinkler Placement & Uniformity

For the past several weeks or years, part of our campaign to reduce water has been to check your irrigation equipment. Many listeners have not understood some of the design criteria and so these are some ideas on design and use. Most sprinklers and spray heads spray water in a circular pattern. Just as a race car driver on the outside corner has more ground to cover than a driver on the inside corner, a sprinkler’s stream has to cover more ground as it gets farther away from the sprinkler head. This means that more water is applied near the sprinkler, with less applied as the distance from the sprinkler increases. If you place one sprinkler on the ground alone and operate it, you have a green area right around the sprinkler with plenty of water. The grass gets progressively lighter shades of green as you move away from the sprinkler until you get a brown area near the edge of the sprinkler’s throw. To overcome this problem and obtain good, uniform coverage, sprinklers and spray heads are placed so that their stream of water touches the next sprinkler. This is called head to head coverage. This complete overlap insures good uniform coverage and reduces "brown spots" in the lawn. At first glance this sprinkler-to-sprinkler placement looks like needless excess, until you see an improperly designed system with brown areas between the sprinklers! Proper initial design prevents many problems later. Sprinklers can be pop-up or stand-up and can operate by impulse (the oldest type), gear drive or rotor drive. Sprinklers shoot a single stream of water and rotate that stream in a circle. They are set to cover a full circle or part of a circle. Typical sprinklers cover an approximately 80-foot circle and have flows of from 2 to 8 (or more) gallons per minute. Application rates of sprinklers can be 1 inch per hour or more depending on nozzle size and pressure. Sprinklers are typically used for large lawn or shrubbery areas. Spray Heads: Spray heads can also be pop-up or stand-up. These heads come in preset patterns of throw (90 degrees, 180 degrees, etc.) and spray water over the entire coverage area simultaneously, therefore the term spray head. Typical spray heads cover approximately a 30-foot circle and have flows of from 0.3 to 3.7 gallons per minute depending on size and pattern. Application rates of spray heads can exceed 1½ inches per hour. Spray heads and sprinklers cannot be placed on the same irrigation zone because spray heads, while covering a smaller area, apply water to that area at a much higher rate. Spray heads are typically used on shrubbery and small lawn areas. Avoid using them on slopes because they usually apply water faster than it will soak into the soil. Larry A. Sagers Regional Horticulturist Utah State University Extension Thanksgiving Point Office