Simplifying The Science of Slope Irrigation

Industry Tips for Proper Sprinkler Installation on Those Challenging Slopes

In collaboration with Hunter Industries and Jodie Carter, regional editor

If possible, use low-angle trajectory nozzles for zones near the top of the slope to reduce wind drift. (See A on diagram) Because low-angle heads have less radius of throw (at the same pressure and discharge rate) than a standard 25-degree trajectory sprinkler, they should be spaced a little closer together (to increase the precipitation rate) and installed vertically. If standard nozzles are used, tilt the heads toward the toe of the slope (see B on the diagram) and install slightly down from the slope?EUR??,,????'???s top edge to decrease wind drift.

Mid-slope heads (see C) should be installed at an angle halfway between vertical and perpendicular to the slope is recommended. But, heads at the toe (see D) should tilt slightly away from the slope to avoid driving water into the slope directly in front of the sprinkler.

Landscape contractors who install or maintain turf know that irrigators on slopes offer greater challenges than a typical flat turf area. When approaching new installations or adjustments on a sloped site, consider that you?EUR??,,????'???ll need to quantify the angle of the slope and the exact dimensions of the area to be irrigated. Next, compare the application rates of different types of sprinklers and select the type that is most appropriate.

In general rotors have lower precipitation rates compared to sprays and are good for use on slopes. If the area is too small for rotor irrigation, then drip or micro irrigation products might be better suited for your application.

If the top or toe (bottom) of the slope is an area of pedestrian traffic, pop-up type heads help prevent trip injury and damage to the system. Many manufacturers product 12-inch pop-up sprinklers for use with taller ground covers.

All pop-up sprinklers should be installed on swing joints so that the angle can be adjusted without applying twisting stress to the lateral lines. (See figure 4A). With shrub-type sprinklers, once the position of the riser and degree of sprinkler head tilt is set, rebar should be driven into the ground at the same angle. Secure the sprinkler to the stake with a staking kit (available from manufacturers). Some specs require stainless-steel hose clamps be used to attach sprinklers to stakes. If so, be sure the screw is also stainless or it will corrode and eventually let the sprinkler fall out of the proper angle.

Sprinklers installed on slopes will produce an elliptical wetted pattern; the downhill throw will be increased, while at the same time the uphill throw is decreased. Because of this, sprinkler spacing will need to be adjusted to provide uniform coverage.

A general rule is to decrease the row spacing across the slope by one percent for every one percent increase in a slope over ten percent. For example, if the slope is 16 percent and the radius of the sprinklers is 50 feet, you would decrease the spacing by six percent or three feet (50 divided by 16 equals 3.125).

The row of heads closest to the top row of sprinklers on the slope will throw short of their desired radius and the row closest to the bottom row will throw beyond their desired radius. To correct this, it?EUR??,,????'???s necessary to shift the interior rows of sprinklers toward the top row by the amount that the uphill throw is reduced.

These spacing alterations are suggested in addition to adjustments made for wind conditions, relative humidity or other site-sensitive variables.