Irrigating Difficult Spaces
Distinguishing yourself in the irrigation business is a perpetual challenge. Competition is intense and the battleground is littered with casualties of the low-bid war. Too often we choose to compromise profit rather than win the battle of innovation and ideas. Having been in the irrigation business for more than 30 years, I attribute my longevity and success to being innovative and creative in design, utilizing the latest technologies and products, and taking a holistic approach to design and installation.
Over the years, I've built my company identity on being able to handle difficult landscape situations. As a regular subcontractor for several landscape architects, I am often selected for the “difficult jobs” — those with complicated microclimates, unusual landscape designs and intensive management requirements. In this article I will share my overall design philosophy and approach to meeting common challenges in irrigation design, and share some of the ideas, techniques and design methods that I find successful in addressing unusual situations. Of the challenges I face in irrigation design, trees, stair-step landscape design, slopes, pots and planters are the most difficult.
It's been my experience that the most difficult of all plants to design for are trees. Trees are usually specially selected by the customer for their visual appeal, sentimental value and as a long-term investment in the property itself. They are also generally the most expensive plant specimens. For these reasons, you must give special consideration to ensuring that the trees survive the initial shock of planting, and give them the best chance of a long, productive life.
With few exceptions, group newly planted trees on their own zones (or valves). This allows for more precise control of water application. As trees mature and root zones expand, this “temporary” system may be turned off altogether depending on the root profile and water requirements at maturity. For small trees (10 to 15 gallon sizes) use either 6-inch spacing or in-line drip tubing, installed in a concentric-circle design around the base of the tree. The number of concentric-circles depends upon the size of the excavated area around the tree and soil type. The close emitter spacing and slow application rate of the in-line drip product provide a good wetting pattern around the root ball without drowning the tree. This is a common cause of tree death in heavy clay soils.
A second design approach is more applicable to large tree specimens — those typically larger than 60 gallons. For trees of this size, providing an even distribution of water to the fine root hairs across the large root ball is sometimes difficult. Rather than using bubblers and drip tubing, use flat-angle, fixed-spray nozzles that irrigate the excavated area and root ball. The high application rate of fixed-spray nozzles is generally not a problem since the root ball and surrounding soil typically have a high water-infiltration-rate potential. Again, isolating these trees on their own irrigation zone is critical for control.
Another common challenge is the common “stair-step” planting design. With this arrangement, larger plants are placed in the back, usually against a structure (house wall or fence), and plants “step” down in size toward the front of the planting bed. For me, the objective is two-fold: 1) to prevent water stains on windows, walls and fences, and 2) vary water application rate to accommodate optimal plant water requirements for each “stair-step.”
My approach to solving this particular challenge is also two-fold: 1) use flat-angle, closely-spaced, high-precipitation-rate nozzles positioned a minimum of 6 inches from the structure itself and that spray underneath the canopy, and 2) employ what I call the “disproportionate nozzle selection technique.” Using this technique, vary irrigation application rates through nozzle selection, thereby accommodating rows or groups of plants of different sizes and water requirements. For example, high-application-rate nozzles are placed in the rear of the bed to water larger plant specimens, while lighter application rate nozzles are used for middle and front bed specimens.
Since many planting beds slope away from structures, a certain amount of water will move down the slope (or to the front of the bed) from gravity and capillary water action. To prevent water stains, use a variety of specialty low-angle or flat-spray nozzles at a low height. This minimizes wind drift and over-spray. If the planting pattern and density allow, use multiple rows of 6-inch spacing, in-line drip tubing. I tend to use this design if the particular plant species has a lower water requirement relative to the surrounding plants. Although this design approach does sometimes clash with other philosophies of irrigation design (particularly those that propose equal application rate at all costs within a single zone), it is one way to limit the number of irrigation zones in a design, while at the same time addressing the different water requirements in a single planting bed.
Slopes pose a significant challenge for all irrigation designers. The degree of difficulty varies with steepness, soil type (infiltration rate), level of compaction, plant type, plant density and proximity to critical surfaces (sidewalks and streets, for example). The goal is simple — to prevent water runoff and minimize erosion. With sprinkler systems, keep irrigation application rates as low as possible. This is difficult to do when the area is small and slope is steep, considering that the application rate for fixed spray nozzles is relatively high. Factor in compact or clay soils with slow infiltration rates, and your design options using spray systems are limited.
To minimize runoff: 1) use square rather than triangular sprinkler spacing, and 2) separate the top and bottom of the slope into different zones and vary nozzle trajectory and pop-up height. Square spacing provides good coverage, yet applies a lighter application rate compared to triangular spacing with the same nozzle. For the top zone, I prefer a flat trajectory or low-angle nozzles, and sprinkler heads with a low pop-up height. For the bottom zone, maximize spray radius and spray pattern distribution by selecting a nozzle with a steeper spray trajectory and sprinkler heads that pop up higher than those on the top of the slope. Generally speaking, the steeper the slope, the higher pop-up height for sprinkler heads positioned at the bottom of the slope.
POTS AND PLANTERS
Over the last few years, more and more customers have recognized the aesthetic value of decorative pots and planters. These days, nearly every landscape design features pots or planters. Fortunately, the product options for irrigating pots and planters have also expanded.
The difficulty with irrigating pots is maintaining adequate moisture while preventing water staining on expensive surfaces. When possible, try to provide input on the front end — expressing the need for a good pot medium that has high-water-retention capillary action properties. This definitely helps control moisture level in the pot, however, too much water retention can lead to waterlogged soils, anaerobic conditions inside the pot and poor plant quality.
For pots and planters, the soil mix and water retention properties are a key determinant in design. In pots with porous soils, use one or more micro-spray (or micro-mist) applicators at the surface of the soil to ensure that the entire soil surface is wetted. In heavier soil media, use closely spaced, in-line drip tubing, positioned such that emitters are at the base of plants. Understanding the water-retention quality of the soil medium is also important in scheduling pot irrigation systems. Isolating pots on their own irrigation zones is a must, and necessary to prevent over-irrigation, which can stain other surfaces.
From my experience, soil is the key variable to understand when designing for difficult situations. Understanding soil and the part it plays in efficient irrigation design is a continuing process. The knowledge I've acquired (and continue to pursue) through experiences (both good and bad), experimentation, research and educational courses, such as those taught by the Irrigation Association, pays huge dividends. As an irrigation contractor, your ability to respond to difficult design challenges with knowledge, creativity and innovation will distinguish you from the pack. That I've remained in business for more than 30 years is testament enough that this is true.
Gene Barnes, CID, CIC, CLIA and Texas Licensed Irrigator 1915, is also president of Gallion Irrigation (Houston, Texas).
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