Meeting plant requirements and managing irrigation systems
can be a difficult task under normal circumstances. When slope
plantings are involved, applying water efficiently and effectively
can be extremely challenging. Too little water and plants
won't grow, too much water and you've got other problems.
Several tactics can be utilized to help you deal with these
ups and downs. Following are ten design and product application
tips for effective slope irrigation.
Tip #1: To reduce run-off, select an irrigation
timer that controls your water applications.
Choose an irrigation timer with at least four start times
per program. Determine how long a station can be on before
run-off occurs. Divide the run time necessary to meet the
plant water requirements by this factor. If necessary, use
each start time and reduce run-off that results from running
valve stations too long. Even better, use an advanced controller
with a feature like Cycle+Soak™. This will allow the
total irrigation run time to be simply split into usable cycles,
and the application of water in intervals that the soil will
easily accept.
Tip #2: Use master valves and flow sensing
equipment as an insurance policy.
It's important to use a master valve when irrigating slopes.
Strategically locate the master valve to reduce the length
of constantly pressurized mainline around the slope, and before
the zone valves. A normally closed master valve will supply
a mainline with water only when a cycle is initiated from
the controller. This equipment will reduce the time that a
damaged sprinkler, a broken pipe, or a defective valve will
have to wash away the landscape.
Flow sensing equipment can detect excessively high flows
when a problem occurs. If calibrated properly, the flow sensing
equipment will work in conjunction with the master valve to
shut the system down and eliminate significant damage during
an excess flow condition.
Tip #3: Use reverse-flow valves to reduce
problems associated with a worn diaphragm.
The inner workings of a reverse flow valve will prevent water
from continuously flowing if the diaphragm is torn. In other
words, it is effective because it will fail in the "off"
position. A valve without a reverse flow feature can fail
in the open position, run continuously and erode the slope
until it is repaired.
Tip #4: Use pressure compensating/regulating
devices to get the best sprinkler coverage.
When used in accordance with the manufacturer's specifications,
pressure-regulating modules can be installed on valves to
adjust the operating pressure of sprinkler heads down stream.
Sprinkler nozzles that are provide the optimum pressure distribute
water as efficiently and uniformly as possible. Sprinkler
nozzles operating at pressures significantly above or below
the optimum usually perform poorly and, as a result, plant
material suffers.
Built-in pressure compensating or regulating devices provide
the best option since the optimum operating pressure is delivered
directly to each sprinkler head. This will eliminate misting
caused by high pressures, reduce water drift due to wind,
and give the water droplets the best chance of getting to
where they are designed to go.
Tip #5: 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, and the effect of the slope cannot be accurately
portrayed.
Therefore, sprinklers can be spaced consistently along the
lateral, but the distance between bottom and middle laterals
should be reduced and moved up toward the top of the slope
to obtain head-to-head coverage and compensate for the true
effects of the slope.
Tip #6: 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 resulting from the elevation change could create
severely uneven pressures at each of the sprinkler nozzles.
This will cause irregular water distribution. Additionally,
the higher pressures at the bottom could shorten the longevity
of the pipes and sprinklers.
Tip #7: Limit sprinkler heads on a valve
zone to decrease potential damage.
As you add more sprinkler heads to a zone, the size of the
delivery system components and infrastructure will increase.
In this case, bigger also means that more water will be available
to cause damage in the event that something on a system breaks.
Consequently, large zones are not recommended unless other
safeguards are included to circumvent potential problems.
Tip #8: Limit sprinkler heads on a valve
zone to increase performance.
Tailor the irrigation system to meet the specific water requirements
of the slope areas. Separate zones to apply water to slope
sections with considerably different plant material, as well
as different exposures to sun, wind and other climatic influences.
If you mix zones together, it will be hard to keep plant material
healthy because one side of the slope will get too much or
too little water.
Tip #9: Place part-circle sprinklers on
separate zones or use matched precipitation rate nozzle packages.
Uniform water distribution is critical for effective slope
irrigation. To achieve this, separate part-circle sprinklers
from full-circle sprinklers, and then adjust the station 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.
Using matched precipitation rate nozzles on the same valve
system reduces the chance that your system will put down too
much water with some heads and not enough from others. This
will help to diminish the potential for severe soil erosion.
Tip #10: Install sprinklers with check valves
to contain erosion.
When used properly, a check valve will contain the unpressurized
water in the lateral lines after the zone valve has completed
its watering cycle (if the valve is located at a higher elevation).
Without a check valve, the elevation difference from a valve
above to the sprinklers below could generate enough internal
pressure to force water out of the sprinkler.
A check valve will prevent the water that remains in the
pipe from draining out of the sprinklers after the valve has
shut off—thus reducing the chance of erosion of the
landscape areas around or on the slope. 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 highly efficient Landscape Dripline which offers controlled release watering to help eliminate runoff and encourage healthy root growth. Not only will the landscape dripline
improve the visual impact of the site, it isn't visible,
and may help cut down on vandalism.
Effective slope irrigation is a mixture of good upfront planning,
proper installation, and a solid maintenance technique. If
all three are done properly, many emotional, financial, and
physical problems can be avoided—and a healthy, aesthetically
pleasing slope planting will be the result.
