Dealing with Slope Irrigation

Meeting plant material water requirements with irrigation systems can be a challenging task under normal circumstances. When slope plantings are involved, applying water efficiently and effectively can be extremely challenging. Too little water and nothing will grow, too much water and you've got erosion problems. If this sounds familiar, read on.

From controller programming to selecting the correct sprinkler, several tactics can be utilized to help you deal with the ups and downs of slope irrigation.

Tip #1
Look for controllers that can limit run times and have multiple start times.

Choose an irrigation controller that will allow you to apply several applications of water during a watering cycle. Do not exceed the infiltration rate of the soil. Applying too much water on a flat areas will cause puddles. When too much water is applied to a slope, erosion will occur.
Select an advanced controller with a feature like Cycle+Soak™. This will easily allow the total irrigation run time to be split into usable cycles, thereby minimizing runoff.

Tip #2
Space lateral lines across the slope rather than with the slope.

When installing the lateral lines, make sure they follow the contours of the slope. If lateral lines are incorrectly installed from the top to the bottom of a slope, the pressure differential by the elevation change will create severely uneven pressures at the sprinkler nozzles. This will cause irregular water distribution. Additionally, the higher pressures could damage pipes and sprinklers.

Tip #3
As an insurance policy, use a master valve and flow sensing equipment.
It's very important to use a master valve when irrigating slopes. Locate the master valve as close to the point of connection as possible and before the zone valves. A master valve only turns on when the system is running. A master valve prevents the mainline from being pressurized unless the irrigation controller initiates an irrigation cycle.
Flow sensing equipment can detect excessively high flows, which are usually created if a pipe breaks or a sprinkler is damaged. If a pipe or sprinkler failure occurs, this will minimize damage to the slope.

Tip #4
Keep zones as small as possible.
Smaller zones will allow you to tailor the irrigation system to meet the specific water requirements of the slope areas. Separate zones to apply water to slope sections with different exposures to sun, wind and other climatic influences.

If mixed, it will be hard to keep plant material healthy due to one side getting too much or too little water. Pressure regulating modules can be installed on some valves to assure that nozzles are distributing water as efficiently and uniformly as possible.

Tip #5
Use pressure regulating nozzles.

When used in accordance with the manufacturer's specifications, sprinklers with built-in pressure regulating devices will maintain a constant pressure, despite the variance in pressures created by elevation differences. This will eliminate the misting or fogging caused by high pressures, stops water waste and will restrict water loss if a nozzle is removed or damaged.

Tip #6
Place part-circle sprinklers on separate zones or use matched precipitation rate nozzles.
Uniform water distribution is critical for effective slope irrigation. To achieve this, separate part-circle sprinklers from full-circle sprinklers and adjust the run times. An easier method is to use nozzle sets that are specifically designed to create consistent precipitation rates, despite the various arcs and radii.

Regardless of the method you choose, using matched precipitation rate nozzles prevents the system from putting down too much water and helps eliminate the potential for severe soil erosion.

Tip #7
Adjust the distance between lateral lines to compensate for the slope.

On a 2:1 slope, a properly adjusted sprinkler will throw about 80 percent of its radius above the head and 120 percent of its radius below the head. This concept is difficult for many people to understand because, on the site plan of an irrigation project, slopes appear to cover less ground than they actually do.

While planning for slope irrigation, remember that the true size of a slope cannot be represented on a two-dimensional plan. You will find that the slope is represented much shorter than it actually is in order to give the appearance of relative size. In other words, there is more area to be irrigated than you initially think or is indicated on the plan.

Sprinklers can be spaced consistently along the lateral, but distance between laterals needs to be adjusted. Adjust along the bottom and middle laterals to compensate for the slope.

Tip #8
Use reverse flow zone valves.

A reverse flow valve is effective because, if the diaphragm gets torn, it will stay closed or fail in the closed or "off" position. A valve without a reverse flow feature will fail in the open position and run continuously until the problem is detected.

Tip #9
Install the mainline at the base of the slope.

Installing the mainline along the base of the slope is a great preventative measure to guard against potential problems if it fails. If a mainline is installed at the top of a slope and it fails, catastrophic water erosion could occur.

Tip #10
Install check valves at the base of each sprinkler.

A check valve will contain the water in the lateral lines after the system has completed its watering cycle. This prevents drainage from sprinklers that can lead to flooding and erosion. Also, a check valve installed at the base of each sprinkler will minimize water hammer during start-up.

Look for sprinklers that have built-in check valves. This eliminates the need for a separately installed check valve under each sprinkler.

An Added Benefit
Because many slopes are planted with ground cover instead of turf, consider installing 6- or 12-inch, pop-up sprinklers rather than riser-mounted sprinklers. Not only will the pop-ups improve the visual impact of the site, they aren't as visible and may help cut down on vandalism.

Effective slope irrigation is a mixture of good upfront planning and proper installation technique. If done properly, it will not only make for a happy customer, you'll avoid costly call backs.