How To Find The Precipitation Rate

How to Find The Precipitation Rate For Your Sprinklers

Knowing each zones precipitation rate for your sprinkler system is crucial for setting a proper watering time. It will allow you to make sure your plants get all the water they need while not going over your soil’s infiltration rate. When that happens you get water run off and waste.

There are many ways to do this and a helpful chart to follow. You’ll have to find out a few things about the zone you want to start with first. It’s important to know that every zone must be done separately.

You’ll have to look find at least one full spraying head, meaning 360° spraying. The nozzle should show a GPM (Gallons Per Minute) on there. If it doesn’t but shows the brand and model, you can look up that nozzle chart online. Otherwise, you’ll have to do it manually by using the formulas. You’ll also have to find the spacing between each head in feet.

Ideally, they all your nozzles are the same brand. This is how we get a matched precipitation rate. So, every nozzle distributes a proportional amount of water in comparison to each other.

Spray head nozzles match themselves if they are all from the same manufacturer. With rotor heads, you must match them manually. So, if you have a 6.0-gallon nozzle on a 360° head. To match your precipitation rate, you must put a 3.0-gallon nozzle anywhere you are only spraying 180°, and a 1.5-gallon nozzle spraying 90°. This is matched precipitation.

You can also get the GPM by watching the water meter while running that zone. Once you know your GPM for that zone, we also need to know how far apart the heads are from each other on that zone. Then line up your answers on the chart to find your PR (Precipitation Rate).

You can find your Precipitation Rate using the chart or manually using these different formulas.

How To Find Precipitation Rate - Lawn SenseTotal Area Method for Precipitation Rate:

One of the preferred methods because it accounts for all heads at once. You can get this number by watching your water meter or a flow meter.

Precipitation Rate = 96.3 X Total GPM/ Total Area Covered by That Zone

(GPM – Gallons Per Minute)

Specific Area Method for Precipitation Rate:

Popular for calculating one zone at a time.

Precipitation Rate = 96.3 X GPM (Of one 360° head) / Head Spacing X Row Spacing

(GPM – Gallons Per Minute)

Triangular Spacing Method for Precipitation Rate:

For heads spaced in a triangular spacing fashion.

Precipitation Rate = 96.3 X GPM (Of one 360° head) / (head spacing)2 X 0.866

(GPM – Gallons Per Minute)