Irrigation systems should include separate zones to accommodate different watering requirements, drip irrigation for plant beds, and rotating sprinkler heads for turf areas that should be laid out to avoid duplicate coverage and watering paved areas and buildings. Surface runoff can be reduced by keeping the precipitation rate from sprinklers below the soil’s infiltration rate, and establishing different zones for the tops and toes of slopes.
Overwatering is a major problem, according to results of a new EPA water-use study. In fact, 62% of the homes in the national study exceeded the theoretical irrigation requirements (TIR) for their sites by as much as 187%—mostly due to owner error in setting and maintaining timer-based controllers.
The Irrigation Association’s (IA) Smart Water Application Technologies (SWAT) program, a partnership between water utilities and industry representatives, promotes the use of “smart” irrigation control technology that uses climate, site, horticultural, and/or soil moisture information to adjust irrigation to conditions on the site.
Case studies carried out by the IA suggest that systems that use smart controllers can reduce water use by 20% to 40% compared to timer-based systems. While the price of a sophisticated system will depend on the number of zones and specific features, it isn’t necessarily steep. “Products coming out now are very comparably priced to traditional [timer-based] controllers,” says Brent Mecham of the Irrigation Association. “And often you can add new technology on to an existing controller to make it smarter.”
The IA has developed a testing protocol for climate-based controllers, which schedule irrigation based on a range of site-specific weather data. More than 25 products have been tested, and performance summaries and technical reports on each of them are available from the IA (www.irrigation.org).
The association is also developing a protocol for soil moisture–based sensors, which schedule watering based only on soil moisture levels. Calibration reports are available for products tested during the first phase. Other protocols under development at the IA offer guidance on sprinklers, rain sensors that shut off timer-based systems when irrigation isn’t necessary, and add-on devices to update and refine the programming of existing systems. A WaterSense certification for weather-based controllers, which will verify performance as well as conservation, is in the works from the EPA.
On small sites, or on sites that have hardscaped areas that don’t require any water, micro-irrigation is an option. These are low-pressure systems that spray, mist, sprinkle, or drip water close to a plant’s root zone through plastic hose lines or small emitters. These systems lose little water to evaporation, wind, and runoff, and they also can be used within multi-zone designs.
Even with all of the available technical data and certification programs, it’s best to use an installer with knowledge of soil science, grading, and other factors that will help ensure a system is tailored to make a landscape thrive. The IA offers certification programs for irrigation designers, contractors, and auditors, and the WaterSense program includes irrigation partners.
LET IT RAIN
In areas where rainwater is available and local regulations allow, rainwater harvesting is gaining attention as an alternative source of irrigation water. These systems can be as simple as a rain barrel connected to a soaker hose or as sophisticated as a large underground cistern connected to a pressurized irrigation distribution system. The more complex systems require components that might be new to irrigation contractors, including debris excluders; first-flush diverters; quiescent inlets; floating inlets; and the controls, filters, and disinfection systems designed specifically for the catchment system volume. The amount of water that can be harvested is determined by calculating the size of the roof area and the typical amount of rainfall.
In some places, due to water rights issues and health and safety concerns, water harvesting is closely regulated, but already Georgia, Oregon, Texas, and Virginia have published code addenda addressing rainwater systems, and last year the ICC collaborated with the American Rainwater Catchment Systems Association to provide rainwater systems language for the International Green Construction Code now under development.
And finally, harvesting, or simply redirecting water from downspouts to plants (along with utilizing porous materials for non-planted areas) keeps runoff out of the sewer system, easing stress on infrastructure while allowing more water to percolate back into the groundwater. Water from a small roof area can simply be sent to a lawn or planting bed; larger amounts can supply a specially designed rain garden that is graded to collect water, filled with well-drained soil, and planted with species that can tolerate inundation as well as drier periods in between storms. Some local governments offer design assistance or even grants to expand the use of rain gardens and other techniques that treat rainwater as a resource, not a waste product.
Linda McIntyre is a contributing editor for Landscape Architecture magazine.