Subsurface Drip Irrigation Guide - Page 7

Of all the calculations, this one should be memorized, because doing this math quickly is what can help make system design go faster.

Example: We have a 1,000 square foot area to irrigate. It's a turf area with clay soil. By checking the General Guidelines chart, we see that 0.26 GPH/18" dripperline on 18" to 22" rows is called for. Since the formula tells us to divide by the minimum recommended row spacing, 18", that's what we'll do.

While the formula is accurate, there are any number of geometric shapes that an area may have. By using the minimum row spacing, you'll never end up on a job site with too little dripperline. So even if you have to move the rows out an inch or two, you will not run short.

Note: Formulas like this are not intended to replace the skills of a designer.

Netafim USA recommends that dripperline be buried anywhere from just below the surface to about 6". We also recommend trying to keep the burial depth consistent.

The deeper you bury the dripperline, the more work it will take to bring the water close to the surface. The result is that you will need to bring the rows closer together to do it. When you see deeper burial depth recommendations from other companies, it may be an effort to protect chemically-impregnated dripper from hot soils. Because the chemical is very sensitive to heat, burial depths of 8" are common, but can be more labor intensive to install.

If the Netafim USA General Guidelines Charts are followed, Techline CV and Techline may be used anywhere from on-surface to 6". The issue about consistency in burying depth has more to do with creating an even wetted environment to the same height, width, and depth across the zone.

Figure 30 - Examples of wetted pattern of Techline CV after running for four minutes and prior to being covered with topsoil.

Note: Past claims have been made that dripperline can be buried 1" or 2" deep in soil even though published applications for the product clearly show that the product is designed for non-subsurface applications. Soil is soil, whether it is 1" deep or 6" deep. The issue is not whether "being one or two inches deep is nothing more than being under mulch," but rather the dripper's inability to guard against root intrusion. If the catalog doesn't clearly call out a subsurface application that includes turf, it shouldn't be used anywhere but on-surface, where the roots won't be.

A myth that nay-sayers use to dissuade you from using subsurface drip irrigation is, "you must have all dripper emission points at the same depth all along the run, because if you don't, this will affect the evenness of the water distribution."

Figure 31 - A Vermeer® LM42 laying Netafim dripperline over three rows at a time.

The reality is that if you follow the General Guidelines Chart for what you are irrigating, Netafim has already determined the water's ability to move in the soil. The dripper overlap pattern is such that the water is radiating out past any neighboring drippers. With that as the case, you end up with a very well-balanced application of water. In fact, far better than anything you could create with sprinklers.

Subsurface Drip Irrigation Guide - Page 7