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 have 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 which 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 to reduce run-off resulting 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 simply be split into usable cycles and the application of water into intervals the soil will easily accept.
Tip #2 - Use master valves and flow sensing equipment as an insurance policy.
It is 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 a damaged sprinkler, 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 which are provided 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 more water will be available to cause damage in the event 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 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 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 which 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-inch 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 are not as 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.
Straight Talk About Slope Installations
Irrigating sloped areas is not difficult, but does need to be handled with several things in mind. Above all, it must be understood that to view a slope on an irrigation plan means to view it on a flat surface. Thus, the angle of the slope needs to be accounted for and the exact dimensions of the area to be irrigated needs to be determined.
Once the area's size has been established, consider the application rates of different sprinklers and carefully select the type which is most appropriate. In general, rotors have lower precipitation rates compared to sprays and are better suited for use on slopes. If the area is too small for a rotor, drip or micro irrigation technology may need to be used.
If possible, use low-angle trajectory nozzles (A) for zones near the top of the slope, to reduce wind drift. These heads have less radius of throw (at the same pressure and discharge rate) than a standard 25° trajectory sprinkler, so they should be spaced a little closer together (this will increase precipitation rate) and installed vertically. If standard nozzles are used, tilt the heads toward the toe of the slope (B) and install slightly down from the slope's top edge to decrease wind drift.
Mid-slope heads (C) should be installed at an angle (halfway between vertical and perpendicular to the slope is recommended), while heads at the toe (D) should tilt slightly away from the slope to avoid driving water into the slope directly in front of the sprinkler.
There are several other variables to consider, including ratio of slope, piping, soils, scheduling and zoning, plus check valves to prevent low head drainage.