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 that 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.

It is also suggested to use the Hunter Staking Kit, which attaches to a piece of rebar and is a safe and secure way to install PGS and I-10 sprinklers in slope applications. The kit (part #46-3551) is available from your local authorized distributor.

There are several other variables to consider, including ratio of slope, piping, soils, scheduling and zoning, plus check valves to prevent low head drainage. For complete information on slope irrigation, download Irrigation Notes: Slope Irrigation (LIT-095).