Dodging Death By Design: Irrigation Design

The realization that irrigation design specifics are not on key in the middle of a system installation can be a frustrating experience, Bob Giordano pointed out.

"Irrigation design is the weakest area of the entire industry," said Giordano, North Bay irrigation manager, Cagwin & Dorward, Novato, Calif., explaining that a poor design can delay an installation a few days or even a few months, depending on how tight a contractor’s job schedule is. "Forty to 50 percent of the designs we get in are done poorly. This can be a nightmare during a busy summer."

Dave Daniell agreed. "The only problem that can delay an installation is getting out in the field and realizing that something is wrong with the design – either there are too many heads on one valve, slope elevation wasn’t taken into consideration or sunny and shady areas of the site share the same zone," said Daniell, vice president, Heads Up Landscape Contractors, Albuquerque, N.M. "Correcting the mistake is always time consuming and costly."

Bad irrigation design also costs the client money. "If a system is designed poorly, especially the system hydraulics, repairs will need to be made more frequently, including valve replacement from excessive wear and plant material replacement if an ornamental or turf suffers as a result of bad head spacing," Giordano said. "Poor irrigation system design threatens the entire life of the system."

By following proper procedures, such as making site visits and calculating pressure correctly, contractors can extend irrigation systems’ lives and save themselves and their clients’ time and money.

BAD TO THE BONE. A poor irrigation system design can be spotted a mile away. The first sign of faulty design is dead plant material, Daniell pointed out.

"If Kentucky bluegrass doesn’t get watered properly, it shows with splotches and dry spots," he said. "Head-to-head coverage is essential when irrigating turf."

Improper design also can be easily red-flagged the moment a system begins running. One hydraulic-related aspect of a system that accentuates poor design is excessive misting from sprinkler heads, Giordano mentioned. "Excessive system pressure is released through mist from sprinkler heads," he explained. "This usually reflects a contractor’s inability to calculate system pressure correctly. He or she probably guessed that using two heads on every section is the safe alternative. By doing this, he or she has under-designed the irrigation system, which means 50 to 60 pounds per square inch (psi) of pressure is being emitted through each pop-up spray head when only 25 psi per head is needed."

In drip irrigation, which is difficult to botch, according to Daniell, contractors tend to run a pipe too long, which can squelch the water supply for plants at the end of the line. "If you run water through a long stretch of pipe, friction will eventually slow it down," he said. "When using ¾-inch poly pipe, the furthest spray head should be no more than 200 feet from the valve."

When water audits are conducted, Giordano said most contractors are shocked at the distribution uniformity that results. This number – calculated as a percentage – indicates how closely the driest area compares to the average precipitation rate of the irrigated area. It also can indicate poor irrigation design. "Distribution uniformity should be at 60 to 80 percent," Giordano stressed. "Most of the time, the number that comes up is much lower than that – 35 or 40 percent on average. This low number means there is a design problem somewhere in the system."

FORGET-ME-NOT. Just as flawed designs can be spotted effortlessly, remembering the appropriate elements involved in proper design to avoid these pitfalls is not difficult.

One of the biggest and most irresponsible mistakes contractors make when designing an irrigation system is failing to visit the site. Without seeing the site, contractors don’t know whether severe elevation or obstacles affecting spray patterns need to be addressed. "A large tree will restrict the spray on a spray head causing dry spots," Daniell remarked. "Contractors receive a site plan, design the system without actually visiting the property and don’t realize that their design doesn’t address these types of site problems."

When elevation is severe on a site, the lateral lines of an irrigation system need to run perpendicular to the slope to prevent flooding and drainage problems, Giordano explained. But without visiting the site, elevation issues aren’t brought to an irrigation contractor’s attention.

A site visit also gives contractors the opportunity to separate areas of severe shade or sun into different zones so the plant material in those areas receive the right amount of water. A sunny area will always need more water than its shady counterpart. Similar requirements are true of the west vs. the north side of a building, Daniell said.

While on the property, checking and comparing the measurements of the plan to the actual site also can save contractors time. "If you’re off just a couple of feet, the plan design can change drastically," Giordano pointed out.

On high-traffic commercial sites, protecting bubblers or sprinkler heads from vandalism is another design element that contractors tend to forget, Daniell commented. "If you’re using bubblers, you may want to put them in a box or container where they are hidden from the public or put a lock on them," he said. "Another option is setting spray heads down lower to save them from being kicked or hiding them so they are more difficult to access."

In new construction areas, Daniell said another key to proper design that contractors overlook is pressure at the point of connection. "Contractors have the tendency not to think about the future of irrigation systems," he explained. "Often, in new areas, pressure will be high, and then as the area is built up and there are more water users, the pressure goes down. Contractors tend to design a system for high pressure and when more people are using that water source, the system doesn’t work well because the system pressure has been thrown off."

A few other aspects of irrigation systems contractors tend to forget during the design process, according to Jeff Lovell, design manager, Century Rain Aid, Madison Hts., Mich., include:

• Water source locations and capacity
• Power availability and voltage
• Exact project boundaries (what is being watered
• Type of soil on the site (sandy soil needs more water than clay soil
• Existing sleeve locations
• Project schedule (landscape, grading, utility and concrete
• Existing site utilities

SOFTWARE SOLUTIONS. For contractors who do a large percentage of in-house irrigation designs, design software can be beneficial, providing automatic counts of items, such as control valves, heads, piping and total materials used. A clean, color-coded, computer-generated design that some software generates also can function as a helpful selling tool. "Computer-aided drafting visuals are cleaner than those that are hand-drawn," said Mike Clark, construction manager and former irrigation manager, The Brickman Group, Long Grove, Ill. Curved lines, however, are harder to draw with software, Clark added.

Daniell has been using design software for approximately five years, and the time he saves is substantial – 30 to 40 percent – when compared to hand drawing. "We still hand draw designs for our residential customers, though," Daniell pointed out. "Homeowners respond better to hand drawings."

Using design software isn’t for everyone. In his 25 years of designing irrigation systems for residential properties, Bob French, owner, French Landscape Irrigation, Edmonds, Wash., has found most design software cumbersome and inconvenient. "It takes so long to use," he said. Unless he has time during winter months to learn a new software package, French said he would rather design the old-fashioned way: with a paper and pencil.

Giordano agreed. "In the future, if computer software manufacturers make design software easier to learn and use, we may try it," he said.

PAYING THE PRICE. Generally, a design’s value should be built into the total cost of an installation job or billed separately. Either way, in order to emphasize a design’s value, its monetary worth should be pointed out during the estimation process, Clark advised.

The average homeowner with a property under 1 acre in size will pay anywhere from $300 to $1,000 for the irrigation design alone, Giordano said, based on man-hours involved and project difficulty.

Water supply also affects a design’s cost. "The water supply for an irrigation system isn’t always coming from the city meter," Giordano said. "Depending on the size of the property, the city meter may not supply enough water to irrigate the property in a 24-hour period. Looping the main lines or providing holding tanks with pumps will cost more money. If there is a lake nearby, though, the fee to draw an unlimited amount of water from the lake may only be $100 or $150 per year. This would bring costs down. The water source is an obvious place to start when design is concerned, but some contractors still skip this step in the process.

"Design is an important step," Giordano continued. "Contractors shouldn’t short cut the design."