Proper Sprinkler Spacing

To achieve a uniform application of water over the irrigated area, the sprinklers must be spaced properly. When operated at the proper pressure, most sprinklers apply more water in the center of the pattern than at the edges. Therefore, they must be overlapped in order to give a uniform distribution. The amount of overlap depends on the sprinkler spacing pattern and the typical wind conditions at the time the sprinklers will be used.

The two types of sprinkler spacing patterns most commonly used are square spacing and triangular spacing. A rectangular pattern may also be used in some instances.

A square pattern is achieved when the distance between sprinklers (S) is the same as the distance between rows (L). The square pattern is usually used in square or rectangular areas, which require part circle sprinklers along the boundaries and in the corners. Table 1 gives the recommended square pattern spacing for various wind conditions. These recommended spacings are based on a percentage of the wetted diameter of the sprinklers as given by the manufacturer's specifications.

An equilateral triangle pattern has all sprinklers an equal distance (S) from each other. With this pattern, the distance between rows of sprinklers (L) is .86 times the distance (S). The triangular pattern is generally used in areas with irregular boundaries or areas that do not require part circle sprinklers along boundaries. Table 2 lists the recommended spacings for the triangular pattern.

You may need to make adjustments in the preceding guidelines because of irregularly shaped areas or obstructions. For instance, the square and triangular patterns can be combined in the same area to avoid an obstruction. Adjustments are acceptable so long as the proper distances between sprinklers are maintained. This process is called a "sliding spacing."

DETERMINING APPLICATION RATES. Sprinklers are selected according to output volume, or gallons per minute (gpm), and wetted diameter (feet). The output volume of a sprinkler is primarily determined by nozzle size and pressure. Though also a function of nozzle size and pressure, wetted diameter is greatly affected by the type of sprinkler.

Generally, the manufacturer's specifications will give the output volume and wetted diameter for different nozzle sizes and operating pressures. If this information is not available, the output volume of a particular sprinkler can be determined by applying the desired pressure to the sprinkler and catching the water in a bucket for one minute. This volume of water can then be measured in gallons to determine a flow rate in gallons per minute.

The best way to determine the wetted diameter is to set up a single sprinkler at the desired height, apply water pressure, and measure the distance of water throw. The type and size of sprinkler selected depends on the water supply available (volume and pressure) and the area to be covered.

Another factor to consider when you choose sprinklers is the application rate. Application rate is the rate (usually given in inches per hour) at which a particular sprinkler applies water to the soil. If the application rate exceeds the intake capacity of the soil for extended periods of time, undesirable puddling and runoff occur. The intake capacity of the soil depends on several factors including soil type (sand, loam, clay), vegetative cover, and slope.

Use the following equation to determine the application rate for a given sprinkler and spacing pattern:

AR = 96.3 X Q divided by S X L

where:

AR = application rate (in/hr)

Q = gallons per minute applied by one full circle sprinkler

S = spacing between sprinklers (ft)

L = spacing between rows of sprinklers (ft)

If the calculated application rate is significantly higher than the intake rate of the soil, select a smaller nozzle size. As another option, use a sprinkler with a larger wetted diameter and increase the sprinkler spacing accordingly.

Where part circle sprinklers and full circle sprinklers are controlled by the same valve, reduce the nozzle sizes on the part circles so the sprinkler output rates are proportional to the area the sprinkler covers. For instance, a half circle sprinkler should put out half as much water as a full circle; a quarter circle sprinkler should put out one-fourth as much as a full circle.

This information provided by The University of Georgia College of Agricultural & Environmental Sciences Cooperative Extension Service.