How To: Irrigate Slopes
Some professionals may think irrigation installation and maintenance are easy, but there is always something that can and will go wrong. Irrigating slopes are growing environments that present a challenge nearly everywhere you go, on pre-existing slopes or man-made berms. Some professionals worry about maintaining the integrity of the slope on the West coast, while others are trying to keep soil well watered in sandy areas and prevent runoff in clay or loamy soils. There are many techniques to try out, but each will need careful consideration of your particular problem area. The following list is not all-inclusive, nor should each item be implemented in your situation. Consider them collectively, and then apply them wisely.
Convert the slope to a series of small terraces that can catch and slow the flow of water down the slope. The terraces would need to be designed with maintenance in mind. If the area is planted in turf, consideration must be given to accessibility and proper maneuverability for mowing equipment. For landscaped areas, the addition of edging may also help hold the water.
If terraces are a possibility, you could also convert a turf area into ground covers. You would have to factor in establishment time to full coverage and the availability of weed control during establishment. Do you have the staff to pull weeds? Are there labor-saving herbicides available? If the answer to these questions is yes, check with local experts for a list of species suited to your area. Convert areas to perennials or ground covers that tolerate exposure and thrive on little water. If turf is the necessary cover, select species that have a higher drought tolerance rating.
If irrigation systems are to be installed or reconfigured, run irrigation laterals across the slope instead of vertically up the slope. This will allow you more flexibility in scheduling and programming for the sloped area. If ground covers or trees and shrubs are installed, drip irrigation may be a possibility. Keep in mind that in many soils, drip emitters will cover only a 36-inch-radius and plan accordingly.
Match the application rate of the sprinkler system to the infiltration rate of the most restrictive soil in the field. Studies show quite a different infiltration rate between soil textures. Some sands may allow an inch of water to infiltrate per hour, whereas many fine-textured, clay soils may only allow 1/10- to 1/3-inch of water per hour. Programming a system to deliver an inch or more per hour is wasteful in such situations. If you are working with clay soils, the system may need to be cycled on and off several times in a 24-hour period to allow a small amount of water to infiltrate at a time, until the appropriate amount can be delivered.
Use a controller with multiple program capacity. This will allow you to water an area more or less frequently and for varying amounts of time, depending on the slope. Better yet, invest in a moisture sensor that can trigger a station to water only when it is needed. Do the math. If you save enough on the water bill, the investment in more sophisticated technology may pay for itself.
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