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Irrigation and Wind

 

Wind can really mess up an irrigation system. Even a gentle breeze will blow around the water droplets from most sprinklers. Realistically, a slight breeze from time to time is not usually a problem. But if you expect a steady breeze on a consistent basis, you should take precautions in your irrigation system design. This FAQ will guide you through the possible solutions to wind problems.

If Possible, Avoid Using Sprinklers:

The best way to deal with wind when designing an irrigation system is to avoid using sprinklers. Anytime you spray water into the air there's going to be problems with the wind blowing the water around. This is simply unavoidable. So the best approach is to avoid irrigation systems that spray water into the air. A drip system is ideal, as the water is dripped directly into the soil from the emitters. Subsurface (underground) drip systems will work for most lawns, however subsurface irrigation is not for everyone. It is generally more expensive than sprinklers and requires different maintenance procedures.

Bubblers are also a good solution, as the water is also applied directly at the soil level. Bubblers work by flooding small areas of the ground with water. Bubblers do not work well for lawn areas, however. The difference between bubblers and drip is in how quickly the water is applied. With a bubbler the water is applied faster than the soil can absorb it, so it spreads out and floods the area. Bubblers are great for shrubs planted in groups on flat soil where the water can spread out. They are not good for slopes where the water will flow downhill and away. Drip systems emit water very slowly and the water soaks directly into the soil without flooding. With a drip system only an area about 3 feet (1m) in diameter around each emitter (or dripper) becomes wet (the size of the area varies with soil type and how much water is applied.) So at least one emitter is required for each plant, for larger plants you might need several emitters. Drip systems work well on slopes. See the Drip Irrigation Design Guidelines for more information.

Re-Design Your Landscape:

Another way to deal with wind problems is through the design of your landscape. In windy areas it is common to design landscapes so that there is no lawn directly adjacent to sidewalks, driveways, roads, buildings, or anything else you don't want to get wet. A typical lawn for a windy area would be designed to look somewhat like a golf green surrounded by shrubs. (Use a rounded shape for the lawn, like a jelly bean or the meandering edge of a mountain meadow surrounded by forest.) The lawn is then irrigated with sprinklers, and the shrubs are irrigated with bubblers or drip irrigation. The sprinklers are adjusted so that the ones on the upwind side spray slightly backwards into the wind, so that the wind blows the water back onto the lawn. In other words a sprinkler that would normally use a half-circle nozzle on the upwind side might utilize a two-thirds circle nozzle so that it sprays back into the wind slightly. On the downwind side the sprinklers are adjusted just the opposite, with the knowledge that water will be blown slightly down wind. So on the downwind side a sprinkler that would normally have a half-circle nozzle might now use a one-third circle nozzle. Because the lawn is surrounded by shrub areas, any water that blows outside of the lawn area will not be wasted.

Sprinklers and Wind:

The remainder of this article will deal with sprinkler systems and the unique challenges that wind presents when designing a sprinkler system.

Don't Water When the Wind Is Blowing:

I guess it is obvious, but it is an important factor so here it is: the best way to avoid wind problems is to avoid the wind altogether. Even in the windiest locations there are often times of the day when the wind doesn't blow as much or as strong. This is typically in the early morning hours. Try to design your sprinkler system so that you can irrigate during these reasonably wind-free hours of the day. This may require you to obtain a larger water source, so that you can irrigate more area in less time. Do a little research to see what time of the day the wind blows the least. In many windy areas the wind dies down a few hours after sunset and doesn't start up again until shortly after sunrise. Use a fully automatic irrigation system and design it so that it can operate during these reasonably wind-free hours of the day.

Will watering at night cause any harm? Watering at night and during early the morning saves water, as there is less evaporation at these times of day. In humid climates watering at night can lead to mold and mildew problems, however this is not typically a problem in windy areas, as the wind tends to quickly dry out the residual moisture on the leaves. A well-established lawn should not need to be watered more than once a day, even in hot, windy areas. Shrubs need watering even less often. So watering at night, rather than during the day, should not be a problem. In hot, windy areas lawns and other plantings will often look wilted by late afternoon, this is often hard to avoid. Watering during the heat of the day typically does not provide much help with this as the problem isn't a lack of water in the ground. The problem is that the plant simply can't pump enough water through it's roots to stay crisp and fresh looking. A healthier plant with more and better roots is the solution to this problem, and watering too frequently can actually cause less roots to grow. During the establishment period for new plantings (typically the first 90 days) it is necessary to water more frequently, a new lawn often needs water every 2-3 hours on a hot afternoon. When establishing a new lawn it is often necessary to hand water some areas when the wind is blowing in order to assure they get enough water.

Sprinkler Head Selection:

Wind impacts sprinklers when it blows the water away from the place where you wanted the water to be applied. This is called wind drift. Two factors have a large effect on the amount of wind drift. The first is the size of the water droplets the second is the size of the water stream.

Spray-type sprinkler heads: Mist and small water droplets are easily blown by the wind. So it is best to avoid sprinklers that create a lot of mist or very small water droplets. Spray-type heads tend to create lots of mist, especially if there is excessive water pressure at the sprinkler head. This can be addressed simply by properly adjusting the sprinkler to minimize the amount of mist created and not over-spacing the sprinklers. A small screw on the top of most spray head nozzles allows them to be adjusted so that there is a minimal amount of mist created. To avoid over-spacing, if the sprinkler company's literature says the sprinkler has a 15 foot (4,5m) radius, then do not space them more than 15 feet apart! Remember that for the most efficient operation, most sprinklers require 100% overlap of the area watered by each sprinkler. Yes, I know that seems like a lot of sprinklers, but it is the way it works, so get used to it. Each sprinkler needs to throw water all the way to the next sprinkler. Low angle sprinklers are generally less affected by wind, however you need to use a sprinkler with at least a 4" pop-up height so that the low-angle spray does not hit the grass.

Rotor type sprinkler heads: Like the spray-type heads they must be spaced so that there is 100% overlap of the watered areas. When using rotor-type sprinklers avoid models that use less than 3 gallons per minute (11.4 l/min) flow. The higher flow rates of larger nozzles result in larger water droplets that are not blown around as easily. Rotors that have multiple streams of water are called stream rotors. Stream rotors can be identified by their appearance when operating, the streams of water look like spider legs rotating around the sprinkler. Stream rotors tend to have very small water streams that are easily moved by the wind. It is probably best to avoid them if you must irrigate when the wind is blowing. The closer the water is to the ground the less likely it is to be blown by wind. So try to avoid sprinklers that have high trajectories. Low angle sprinklers are less affected by wind. The farther the water has to travel through the air, the more likely it is to be blown off-course by wind. Thus in windy areas it is best to use shorter radius sprinklers.

My preference is to base the selection of either rotors or spray-type sprinklers on the size and shape of the area. I generally use rotors in areas where all the dimensions are more than 20 feet (6m). In narrower areas I use spray-type heads. Both sprays and rotors have issues with wind and in my opinion neither provides a clear advantage in windy areas. When dealing with wind, I have found that the type of sprinkler isn't nearly as critical as proper spacing and adjustment.

Head-to-Head Coverage

For more on sprinkler head spacing see the Sprinkler Spacing Page of the Sprinkler Irrigation System Design Tutorial for the correct method of designing a sprinkler system. Wind makes it critical that you design the system properly; the wind leaves you with no room for error in your sprinkler spacing or pipe sizes.

Valve Zones for Windy Locations:

Design your irrigation system so that the perimeter edges on the up-wind and down-wind sides are controlled by separate valves. Wind problems tend to be the worst along the up-wind edge of the irrigated area. In this area the wind blows the water away from the edge, leaving it dry. The next worst area for wind problems is on the downwind edge, where the wind tends to blow the water out of the irrigated area. Put the sprinklers on both these edges on their own separate valve circuits if possible. This allows you to run those valves during more reliably wind-free times of the day. It also allows you to increase or decrease the watering time in those areas to compensate for the wind problems. If cost or another factor makes it difficult to separate both edges, then try to separate only the up-wind edge to the extent possible. It's OK to fudge a little and include a few heads that aren't on the edge on the same valve circuit with the ones on the edge.

Tighten Spacing On the Upwind Edge:

As previously mentioned, wind problems tend to be bad on the upwind edge of the irrigated area. One means of dealing with this is to place the sprinklers closer together on the upwind edge. There is no room for sprinkler spacing errors on the upwind edge. If you're using spray type sprinklers I suggest a maximum distance between sprinklers of 12 feet. Spray type heads used at 12 foot spacings have water droplets that are considerably larger and less susceptible being blown by the wind. If you are using rotor type sprinklers try to keep the spacing slightly closer than head to head. That means the water from one rotor should spray all away to the next rotor along the upwind edge. Don't stretch the spacing at all. When in doubt, reduce the space between heads and add another sprinkler head. On the upwind edge it is always better to have more heads than to have less.

Wind Detectors:

To avoid irrigating during times when the wind is blowing you can use a control system that detects wind. One method of doing this is to install a wind speed monitor nearby. It detects high wind speeds and shuts off the irrigation. It does this in a non-smart way; it just shuts off the power to the valves and irrigation stops. This is a really effective method but there is a drawback- the irrigation gets skipped and the landscape may dry up if the wind blows for several days! So if you use a wind detector like this you need to keep an eye on it, wind can make the landscape dry out fast. Some high-end irrigation controllers are smart enough to know that the irrigation was shut down and will attempt to reschedule it at a wind free time. Finally, some irrigation controllers have a remote programming feature where the irrigation schedule is calculated and controlled by a company for you on a subscription basis. In this case the company determines that the wind is blowing in your area based on a wind detector, a nearby weather station, or the weather forecast. When the wind blows hard enough to be a problem they shut off the irrigation and reschedule it for you.

That's it. These tricks and techniques should help you to have a better irrigation system in windy areas. Remember, the best trick is to avoid the wind by irrigating when it isn't blowing!


 

 

 

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