Irrigation Design Tips for Properly Locating Sprinklers on the Plan

An irrigation system is one of the few items that is purchased and then buried in the ground. Major problems are difficult to correct after a system has been installed, and even minor mistakes in the design or installation phases of the project can be costly to correct. Properly locating the sprinklers is extremely important in helping to avoid errors.

The goal in positioning the sprinklers is to make sure all areas that require irrigation have adequate sprinkler coverage. Remember not to stretch the spacing between sprinklers beyond their recommended ranges. The row of sprinklers on the project that might be eliminated because spacing was stretched on all the other rows will end up costing the system owner more money that what was saved with the elimination of the sprinklers.  The owner will have to apply more water to make up for poor coverage, wasting water and money, and potential shortening the life of the system.

Here are three tips when laying out the sprinklers you have selected for the project.

1. Begin laying out sprinklers in trouble areas first.

“Trouble areas” are those with odd shapes, prominent obstructions, confined spaces or other features that require special spacing considerations. After establishing the sprinkler locations in the “trouble areas,” move out into the open areas by using sliding or staggered spacing.

Using the exact locations of trees on (or to be planted on) the site is important, so you can provide for them in sprinkler spacing. For trees or large bushes and hedges that are not to be irrigated separately, the sprinklers in the area should surround and throw into or under the plants. For the sprinklers spaced too near, the larger foliage acts as a barrier to good distribution. If the tree or large bush can be watered along with the turf or ground cover without over watering, surround it with at least three sprinklers so it doesn’t affect coverage of the other plantings.
A dense hedge can often be thrown into by nearby sprinklers, if not to be watered by bubblers or drip irrigation. If bubblers are to be used for trees or hedges, a low flow bubbler (.25 gpm to .50 gph [0,06 to 0,11 m3/h or 0,02 to 0,03 L/s]) should be used, or a standard flow bubbler (1 gpm [0,23 m3/h or 0,06 L/s] or more) with a basin to catch any runoff.

2.  Where possible, use the same types of sprinklers over a given area.

Remember the next step after plotting the sprinklers is to group them into valve circuits or laterals. If the turf area on your plan is covered by all spray sprinklers except for rotor pop-ups on one slightly wider spot, the rotors will have to be operated on a separate valve from those spray sprinklers. Try not to isolate three or four special sprinklers that will require their own valve if it is not necessary.

3. After locating all the sprinklers on the plan, visually check the entire system for proper spacing and good coverage.

This is the time to make any slight adjustments, add or remove sprinklers and check spacing before drawing in any pipe routing.

Let’s look at some typical sprinkler-locating methods for various types of planting areas.

Small planters and narrow planting beds can usually be adequately irrigated with drip irrigation, flood bubblers, stream bubblers or short-radius spray sprinklers. If a planter is narrow with walled or berm-style borders, flood bubblers can be used to fill the reservoir area under the plants. Slightly wider planting areas can use stream bubblers that can throw gentle streams out to a radius of 5 ft. (1,5 m). Narrow lawn strips can be watered by short radius spray sprinklers with strip pattern nozzles.

In the sample project provided in the Irrigation Design Manual (pg 50) we can see that low-flow drip irrigation has been used for the planting beds. The drip irrigation pipe is shown graphically by a single dashed line winding through the planting beds. The individual emitters are typically not shown on the plan. Areas “D”, “E” and “H” each represent individual drip laterals. The trees in the planting beds will use multi-outlet emitters, with four outlets open. Each shrub has two single-outlet emitters. Because drip irrigation has very low flows, typically measured in gallons per hour (liters per hour) as opposed to gallons per minute (meters cubed per hour or liters per second), drip emitters and sprinklers are never mixed on the same valve.

In the planting beds of area “I,” tiny micro-sprays, or xeri-sprays, that have been adapted to 12 in. (30,5 cm) pop-up spray sprinklers are used. In the one isolated part of area “H”, on the edge of the walkway between the houses, the designer chose flood bubblers mounted on risers for the climbing plants.

Landscaped strips can be irrigated in several ways. For strips that are 4 to 7 ft. (1,22 to 2,13 m) wide, pop-up and shrub sprinklers, or high-pop sprinklers for shrub areas can be used with center strip or end strip spray nozzles. These nozzles have a “bow tie” or half-bow tie pattern and are located down the center of the area. For strips with trees in the center of the shrub or lawn area, the side strip nozzle can cover the area from each edge of the strip instead of the center where the trees would block the spray. Wider strips, more than 6 to 7 ft. (1,83 to 2,13 m) in dimension, can use half circle spray sprinklers throwing in from both edges.

Narrow strips and confined areas often use low-angle trajectory or flat-angle spray sprinklers to reduce the chances of overspray. Variable arc nozzles (VAN, HE-VAN), are used when the standard arc configuration does not provide adequate coverage. The unusual shape of area “G” lends itself to using variable arc nozzles. Half circle nozzles would create overspray into other areas, third and quarter circle nozzles would not provide enough coverage. VAN/HE-VANs are adjustable to any arc from 0° to 360°. Depending on where the project is located, dripline may be required for narrow areas.

In the wider lawn areas, standard arc spray patterns are used. In area “B,” 12 ft. radius (3,66 m radius) spray nozzles are used and in the narrow part of the lawn (area “C”) 10 ft. radius (3,05 m radius) nozzles are used. In area “E” there are very few wide areas, so 4 in. (10,2 cm) pop-up spray sprinklers are used rather than use rotor pop-ups. Because it is subjected to more wind, the U-Series nozzle was selected for the back lawn. This nozzle is less susceptible to wind drift, an important consideration since the prevailing wind is toward the house.

On the irrigation plan, check arcs for the sprinklers are shown. Check arcs represent the maximum effective radius for the sprinkler. Showing the check arcs on the plan gives you a visual indication that all areas are effectively covered. They also point out any areas where overspray may occur. Sprinklers which exhibit overspray can be adjusted in the field using the throw adjustment capability of the head.

Wider, more open areas are easier to design irrigation for than smaller more broken up areas. In the past, small impact sprinklers and rotor pop-up sprinklers had a radius of about 40 ft. (12,19 m) with an adjustment range down to the mid-30 ft. (10,67 m) range. Spray sprinklers were used where the area to be watered was 30 ft. (9,14 m) wide or less.

The 30 ft. (9,14 m) wide area was commonly handled by three rows of 15 ft. (4,57 m) radius spray sprinklers — a row of half circle sprinklers down each edge of the area, and a row of full circle sprinklers down the center.

With the advent of the small turf area rotor pop-ups and small, light-impact sprinklers that have a range from 17 to 40 ft. (5,18 to 12,19 m), the designer has a decision to make for areas in the 20 ft. (6,10 m) range. Beyond 15 ft. (4,57 m) or so, two rows of spray sprinklers would be stretched too far.

However, simply switching to a larger radius may not be the best design answer either. A decision between using three rows of spray sprinklers, or switching to a two-row design with rotating sprinklers, may be influenced by any number of factors.

If low trees would obstruct the longer, higher throw of the rotating sprinkler, perhaps the spray sprinklers are more appropriate for watering the area. Spray sprinklers are often more appropriate for areas that have lots of curving edges. It may be difficult to avoid overthrow or gain complete coverage with a larger radius sprinkler. If low precipitation rates were required for this medium-wide area, then rotating sprinklers delivering less than .75 in. (19 mm) of water per hour would be better than spray sprinklers delivering over 2 in. (51 mm) of water per hour.

Perhaps the higher cost per unit of rotating sprinklers would be more than offset by elimination of the middle row of spray sprinklers because the installation expense of trenching and installation would go down. The decision is up to the designer, who considers the special needs of the site along with practical experience.

In the “Alternate Back Yard” illustration below you can see what the sprinkler locations would have been if the landscape plan for our sample project had a wider, more open, lawn area. Note how few rotor pop-up sprinklers are required for the large area and how low the lateral flows might have changed.

Very large, open areas are the domain of the rotating sprinkler. Large lawns, sports fields, parks, schools, golf courses and agricultural fields allow for the efficient use of large radius sprinklers. The more common rectangular, parallelogram and triangular spacing patterns can be used for maximum spacing and wind resistance.

At this point in the design process, the drawing of the irrigation plan should show every area to be irrigated and designed with properly spaced sprinklers. With this accomplished, the designer is ready to proceed with the next step, which is to group the sprinklers into valve groups.

This design tip was excerpted from Rain Bird's Irrigation Design Manual. To learn about all the irrigation design steps, please download the manual.