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Irrigation: Get the Low-Down on Low-Volume

REBECCA PETERSON | Drip Irrigation - Low Flow

When you’ve been a contractor long enough, it may seem like you’ve seen it all. However, sometimes just when you start to feel this way is when you find yourself presented with a truly challenging project. While the knowledge gained from years of experience is often the best tool for dealing with these situations, the solution you come up with may still have to be as unique as the problem itself.

The building was surrounded on all sides by turf, and its windows extended all the way to the ground. Odd stains had developed on the windows, and it was soon realized that they were residue from hard water sprayed by the sprinkler heads whenever the irrigation system ran. tex3.jpg

At the time, Wilson had already been working with low-volume irrigation for years. It proved to be the perfect solution for the site's problems. "I installed low-volume drip irrigation underground beneath the turf in a ring around the building, and left the sprinklers in place beyond that," he says. The drip system extended for 15 feet out from the base of the building, meaning that the closest sprinklers were 15 feet from the windows.

"The turf looked great, and the sprinklers were far enough away so that over-spray stains on the windows were no longer a problem," says Wilson. "The church couldn't have been happier with the results."

Wilson's experience isn't uncommon -- customers are usually thrilled with the difference low-volume irrigation can make on their properties. Henry Johnson, owner of Johnson and Company, Inc., Advance, North Carolina, says that he once had a customer with particularly voracious chipmunks destroying his landscape.

Even though the chipmunks had repeatedly eaten through lines and damaged the low-volume drip irrigation system, the customer just kept repairing it. He had no interest in switching to a system that would be less vulnerable to rodent damage he only wanted drip. Johnson solved the problem with the use of slightly larger lines; he?s found that on sites with rodent issues, 1/8-inch lines get chewed, while 1/2-inch lines typically don't.

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But exactly what is a low-volume or drip system and how does it inspire this kind of loyalty? You've probably heard a lot of negative stories about low-volume irrigation. You may be surprised to find how misleading these statements are, especially when weighed against the many advantages a low-volume system has to offer.

A little goes a long way

"The concept behind low-volume irrigation is fairly simple," says Rick Heenan, national sales manager for DIG Corporation, Vista, California. "It describes an irrigation system that delivers small amounts of water slowly, at low pressure, at or near the root zone of a landscape's plant material." The amounts and rates of water delivery are so much less and so much slower than the average irrigation system, that the amount of water emitted is measured in gallons per hour (gph), rather than gallons per minute (gpm).

A major difference between a conventional irrigation system and a low-volume system is that a conventional system uses 1/2-inch to 1-inch pipe, while low-volume systems typically use small diameter, flexible tubing because of their lower pressure requirements.

There are four primary types of emission devices in or on the tubing that deliver the water to the landscape: inline drip tubing, point source emitters, micro-sprays, and bubblers.

With inline drip tubing, the emission devices are actually contained within the tubing itself at regular intervals. The tubing is usually buried under mulch or just below the surface of the soil. Point source emitters, on the other hand, utilize external emission devices that can be manually placed as-needed on the line.

Inline and point source represent two different philosophies of drip irrigation. Inline evenly provides water for an entire area, while point source waters each plant individually. Inline tends to be more popular, because you don't have to figure out the needs of different plants, but it works best in densely planted areas, or wherever plants are located in a line or row (such as a row of shrubs). Wherever plants are widely or irregularly spaced, point source is a better idea, because you can place emitters only where plants are located.

Micro-sprays are pretty much exactly what they sound like: very small spray-heads that spray small volumes of water over very short distances. They are sometimes referred to as micro-jets, mini-sprays, or micro-sprinklers. If you want to cover more of a plant's root zone, irrigating a slightly wider area, a micro-spray can be ideal. You may only need one or two micro-sprays to adequately water an area, whereas you might need several more point source emitters to cover the same space.

Micro-sprays can also be a better choice than drip for beds in which flowers are frequently changed. Many irrigation contractors have installed drip irrigation in beds, only to have unknowing landscape contractors come by to change out the flowers and accidentally rip out the drip system as well. Micro-sprays are more visible, and easy to spot and work around.

Pop-up micro-sprays are available for high traffic areas where ordinary micro-sprays might be kicked around or tripped over. This is a concern, especially in commercial applications. When not in use, they sink down until flush with the ground, and some can even be used on systems with high-pressure, underground PVC piping (they contain their own pressure and flow regulating devices).

Finally, bubblers are similar to point source emitters, except that water 'bubbles' out of them, typically either running down the sides of the emitters, or spreading out over a few inches in an umbrella pattern. They are typically seen in applications where more water is required (making drip or micro-spray unsuitable), but is only needed in a small, localized area (where a conventional sprinkler or spray-head is unsuitable). They are often used in planter boxes and tree wells.

4_6.jpgWhy go low flow?

Low-volume irrigation as a whole has been referred to as targeted or precise watering. It targets specific areas rather than casting water out across a broad span. Naturally, sometimes you need to water a large space, and a conventional irrigation system would be a perfect choice. However, with this approach, you may end up watering areas that you don-t necessarily want to water, such as weed-prone bare dirt areas, driveways, and sidewalks.

Irrigating pavement and bare dirt is, quite simply, a waste of water. Wasting water costs consumers more in energy bills, and is environmentally unfriendly. Many states have recently experienced drought conditions, leading to an increasing number of water restrictions.

Because landscape irrigation is one of the most visible uses of water, it has become one of the most scrutinized. In 1992, when Seattle, Washington, experienced a bad water shortage, one of lawmakers' first actions was to cut off all lawn watering. In Florida, laws restricting landscape watering to certain days and times continue to pop up throughout the state. Since low-volume irrigation is considered water-conserving, it is therefore often exempt from such restrictions.

As much of a problem as over-spray is, even water that successfully reaches the plant material it is meant to irrigate can be wasted. "The best analogy to think of is getting your kids to drink their milk," says Susan Thayer, president of Maxijet, Dundee, Florida. "Let's say you want your kids to drink a gallon of milk in a week. They couldn't sit down Monday morning and drink the entire gallon at once. You'd have to feed it to them gradually, a glass at a time, throughout all seven days."

It's the same with plants. If you try to deliver several gallons of water all at once to the plants in your landscape, it's not uncommon for much of it to run off and be wasted. Most soils just can't absorb water that quickly. However, if you deliver those gallons slowly, over a period of several hours, the soil has time to absorb the water and make it available to any nearby plants.

The components used by low-volume irrigation systems also offer several benefits over the components of a conventional system. For starters, the individual parts are often smaller and less expensive than those of a typical sprinkler system.

"Low-volume irrigation has been used in the agricultural arena for years, but it's still a relatively recent transition to the landscape market," says Dave Layburn, senior product manager in Rain Bird's landscape drip division. "Because of that, some contractors don't know how to bid it yet. There's a learning curve. However, after the learning curve, low-volume usually costs contractors less than a conventional system."

5_7.jpgInstallation advantages

Low-volume offers some labor savings as well. The highly flexible tubing means that installing irrigation around irregularly shaped or curved landscape beds is a breeze. Additionally, no trenching or gluing is typically required during installation, eliminating two of the most time-consuming steps in a traditional installation.

"Most contractors would say that installing a low-volume system is easier and less labor-intensive than installing a conventional system. I know I would -- I worked as an installer for years," Thayer says.

Johnson agrees. He once designed low-volume irrigation for the landscape beds at a middle school. He sold the school the various components it would need, and the system was ultimately installed by fifth graders. "It's that simple and straightforward to install," he says.

Even designing a low-volume system doesn't have to be the headache you might think it is -- in fact, one of the most important instructions for anyone new to low-volume is not to over-complicate matters. When designing a conventional overhead system for turf, you may have to perform various calculations, figure out how to match precipitation rates for various areas, etc. Low-volume lessens some of these complexities.

"You don't have to over-engineer a low-volume system," Thayer says. "It's simple -- just cover the entire root area with water." Basic knowledge of the plant material will be your biggest asset -- it's important to know which plants like more water, and which plants like less. Once you determine this, there's a simple way to ensure that each plant gets what it needs.

Let's say you've installed a group of low-volume emitters that deliver one-half gallon of water per hour. However, some plantings need two or three times that amount. Rather than installing a bunch of emitters with different flow rates (1/2 gph, 1 gph, 2 gph, etc.), simply add more emitters at each plant that needs more water.

"You don't have to over-complicate your design by calculating flow rates for a bunch of different emitters, especially if you're new to low-volume. Instead, if a plant needs more water, just place more emitters around it," Johnson says.

Managing maintenance

Maintenance is a huge concern for contractors thinking about working with low-volume systems; you've probably heard numerous times that low-volume irrigation is a nightmare to maintain. That, however, is largely a myth.

Maintenance for a low-volume irrigation system isn't any more difficult than what you'd find with a conventional system; it's just different. Remember, even properly-maintained conventional systems require a fair amount of maintenance, from adjusting or replacing sprinkler heads to re-programming the controller. There's no such thing as a 'maintenance-free' irrigation system.

That said, low-volume systems do have some unique maintenance concerns, such as clogging. Many contractors worry that the tiny, particulate matter all water contains will clog the tiny holes the system uses to deliver water. This problem is almost entirely avoidable -- you just need to keep the water filtered. Filters will keep nearly all particles out of the system; twice-annual flushing further helps keep the lines clean.

Pressure regulators and lines coated with root inhibitor easily solve concerns about blowouts and roots plugging up lines. Ultimately, many of the horror stories you might have heard are from a different era of low-volume irrigation; most of those problems have since been addressed, and there's now some kind of solution to just about every maintenance issue you could encounter.

Training in low-volume is easy to come by, offered by manufacturers and distributors alike. If you've never worked with this kind of irrigation, with prime design/build season right around the corner, it may be a good time to reconsider your position.

 
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