Irrigation rules and design in metro Atlanta

The hours

Georgia law permits outdoor irrigation for the purposes of planting, growing, managing or maintaining ground cover, trees, shrubs or other plants only between the hours of 4 p.m. and 10 a.m. daily. The schedule was added to state law at O.C.G.A. 12-5-7 by the Georgia Water Stewardship Act of 2010, and counties and municipalities were required to adopt it by ordinance. It applies daily rather than on odd and even days, and it applies to anyone supplied by a permitted water system.

Most controllers here end up programmed to run in the small hours, which is where they should have been anyway. Watering overnight or early in the morning loses less to evaporation and gives foliage time to dry before the heat of the day.

The exemptions worth knowing

The statute lists exemptions with no time limitation. The ones that matter on a residential landscape are:

• New and replanted plant, seed or turf in landscapes, during installation and for 30 days immediately following the date of installation. This is the establishment window.
• Drip irrigation or soaker hoses. No time limit at all, which is a strong argument for drip in beds.
• Hand watering with a hose fitted with an automatic cutoff, or with a handheld container.
• Personal food gardens.
• Private wells or surface water on the property.
• Installation, maintenance or calibration of an irrigation system, which is how a technician is allowed to run zones at midday to check them.

What the Metro Water District requires of a new system

Fulton, DeKalb, Cobb and Gwinnett are all among the fifteen counties in the Metro North Georgia Water Planning District. The district's water-efficiency code requirements, adopted as a local amendment to the Georgia State Minimum Standard Plumbing Code, apply to new landscape irrigation systems connected to a public water system. The provisions that shape a design are:

• Pop-up heads must rise at least 4 inches above soil level when emitting water.
• Pop-up spray or rotary heads must direct flow away from adjacent surfaces and must not be installed closer than 4 inches from an impervious surface.
• Areas less than 10 feet wide in any direction must use subsurface irrigation or another method producing no overspray or runoff.
• Narrow or irregular areas less than 4 feet across opposing boundaries must use subsurface irrigation or low-flow emitters.
• A rain sensor shut-off is required and must be left unobstructed.
• A master shut-off valve is required per controller, as close as possible to the point of connection but downstream of the backflow prevention assembly.
• Pressure-regulating devices are required so emission devices run at the manufacturer's recommended pressure.

None of that is exotic. It is the specification a competent designer would produce anyway, which is presumably the point of writing it into the code.

The backflow, which is a plumber's work

Georgia law allows a person to install, alter or repair the plumbing component of a lawn sprinkler system from a backflow preventer which was installed by a licensed plumber. That single clause draws the line: the potable connection and the backflow device belong to a licensed plumber, and everything downstream of it belongs to the irrigation installer. Sandy Springs requires a plumbing permit for plumbing projects.

Backflow assemblies on irrigation systems are also subject to testing. Georgia's rules for safe drinking water require field testing at installation, after repair or relocation, and at least annually, performed by a certified tester. A quote that has no line for the backflow assembly and no mention of annual testing is a quote with a cost missing from it rather than a cheaper quote.

Designing for clay

This is where most existing systems in Sandy Springs go wrong. The Metro Water District puts practical clay absorption at up to about half an inch of water per hour. A typical spray zone applies considerably more than that, so within a few minutes the surplus is running across the surface, and on a sloping lot it runs downhill carrying mulch with it.

The fix costs nothing on an existing system: split each run into two or three shorter cycles with soak time between them, so the total volume goes on but the application rate never exceeds what the ground can take. On a new system, the design answer is to zone by what is being watered rather than by what is convenient to pipe. A bed under a closed canopy and a strip of bermuda in open sun have completely different demands, and putting them on one zone guarantees one of them is wrong.

• Zone by exposure and plant type. Shade beds, sun beds and lawn are three different schedules.
• Cycle and soak. Short repeated runs rather than one long one.
• Drip in beds. It is exempt from the time restriction, it applies water slowly enough for clay to take it, and it keeps foliage dry in a humid climate.
• Check the head layout against the code items above. Narrow strips are where most systems waste water.

Whether a system is needed at all

NOAA 1991 to 2020 normals for the Atlanta area record just under 50 inches of precipitation a year, spread across about 113 days with measurable rain, with July the wettest month. On a well-chosen plant palette in prepared soil, established planting rides out most summers without irrigation. Where a system earns its cost is through the establishment period of a new install, and on turf, which has no drought strategy beyond going dormant.

Plenty of Sandy Springs properties are best served by drip in the beds, a system on the lawn, and nothing at all in the woodland areas. That is a cheaper system to install and a cheaper one to run.

Sources

O.C.G.A. 12-5-7 as added by the Georgia Water Stewardship Act of 2010, for the watering schedule and the exemption list. Metro North Georgia Water Planning District water-efficiency code requirements for new landscape irrigation systems. O.C.G.A. 43-14-13 for the backflow preventer provision. Georgia Rules for Safe Drinking Water, Chapter 391-3-5, for backflow testing. City of Sandy Springs plumbing permits page. NOAA 1991 to 2020 climate normals for Atlanta Hartsfield-Jackson.