Head-to-Head Coverage

My front yard is basically, a 5 x 4 grid of rotors. Each sprinkler sprays to it’s neighboring sprinklers for head to head coverage.

Since every inch of the grass is watered by multiple zones, I like to think of it in “segments.” For example Zone 1 runs 180 degrees and waters only segment A. Zone 2 runs 360 degrees and waters segments A and B at half the precipitation rate as Zone 1.

Do I need to adjust for the fact that zones overlap or is that assumed since it’s best practice?

Does Rachio assume head to head coverage like this? How does it know that segment A is being half watered by Zone 1 and half by zone 2?

A perfectly installed sprinkler system will have overlap just as you are seeing. With rotors, it is a bit tricky because you need to match the nozzles correctly. The rotors that spin 180 will need a “X” PR, and the 360 will need “2X” PR in order to put down the same water in a 360 swing as the 180 does.

At the end of the day, the PR entered into Rachio for the zone can be entered based on whatever your sprinklers put out. If they didn’t overlap, your inches per hour would be one value, with the overlap, its another. Best way to find the nozzle precipitation rate (inches per hour) is to do a catch cup test, or a meter read while the zone is running and calculate based on yard area.

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This is the part I don’t understand. Let’s say I need an inch of water and that my Zone 1 has a PR of 1in/h and my Zone 2 has a PR of 1in/h. Both water the same segment of grass. Am I right that Rachio will schedule both zones for an hour? If so, I get 2in of water put down.

you need to measure entire coverage not just per zone since your zones overlap. This means installing the cups, then running all zones that cover the area you are measuring and only after the last zone runs taking the measurements and doing calculations.

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Ok, I think I get it. Let’s say I need an inch of water and all my zones have a PR of 1in/h. Each segment of grass is watered by 2 zones. I should set my PR rates at 2in/h. That will get Rachio to water for 30m on each zone, giving me my 1in.

If the above is true, it sounds like all of my zones need the same PR not just all heads within a single zone. Thanks for the help.

No, the PR you get from a catch cup test is going to take into account whatever overlap is seen between different heads/zones. Zone overlap can be tricky if the zone attributes are wildly different (shade vs. full sun), which can cause the watering frequencies to get out of sync.

If you are going by the manufacturers specs for nozzles, then they account for overlap in their specs.

1" of PR is 1" of PR regardless if it is being delivered by 1 head or 5 heads.

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This is certainly true, but I’m still lost on how Rachio understands this when it comes to Soil Moisture. Rachio thinks in terms of zones and it tracks Soil Moisture by zone, but Soil Moisture is actually “spot on the lawn” specific, not zone specific since it can be effected by multiple zones. If that spot is hit by 2 zones Rachio’s zone specific Soil Moisture estimate won’t be right because it will be ignoring water contribution from the other zone and vice versa.

I might be over thinking this and probably should just break out the tuna cans and test it out. I do appreciate the help.

Rachio knows these things: 1) how much water soil can hold (Available Water); 2) how deep the water needs to go (Root Depth); 3) how much water is lost over a day (ET/Cc). So with (1) and (2) it knows the total size of the reservoir, if you will. With (3) it can calculate how empty it is. Once it determines that the reservoir’s water has reached the level at which it needs to be refilled (Allowed Depletion), it will use the rate at which water is applied (Nozzle Incher per Hour) to calculate for how long it will need to water. So as you can see, as long as all of your zones have the same parameters, it doesn’t really matter how many there are covering an area.

It is somewhat rare for large areas to be watered by heads from more than one zone. Typically, zones overlap only where one zone meets another, and typically each zone at that point puts out less water, so the overlap can be ignored. Even if you don’t ignore the overlap, and calculate it all out, the result can be at odds to the time for the remainder of the zone. So overlaps are usually ignored.

A case where it CANNOT be ignored is where the same area is actually watered by two separate valves and sprinkler head systems. Like a 20’ x 100’ area with one “zone” on one side watering with 20’ throw to the other side, and another on the other side of the area. Here, each applies about half the water to the actual zone, even though they’re piped separately. Another we had was 3 zones for a rectangular area: on zone with heads along each side of the area, and another in the center of the area. That’s even more complex, or at least different, as each side overlaps the center, but the sides don’t overlap each other. For those kind of situations, they need to be looked at separately and together to get them to work in the best way.

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Another we had was 3 zones for a rectangular area: on zone with heads along each side of the area, and another in the center of the area.

This is the exact scenario I have in my front yard. There is a set of 6 rotors at the curb that water a 180* arc, then another set of 6 rotors at the house sidewalk that water a 180* arc. Then a set of 6 rotors down the center that spin 360* and water from head to head (except on on the end at the driveway at only water 180*).

So what’s the best way to configure the advanced settings so that a Flex schedule is more accurate?

I’m assuming these are on 3 separate zones. A properly designed system like this on a single zone will have the flow rate of the center row of sprinkler heads twice what the ones on the side rows are, because it’s watering twice the area. This may still be the case with 3 separate zones, but as you can compensate with time, they don’t have to be.

Anyhow, I would calculate the Nozzle Inches per hour for each zone by:

  1. Measure the water flow for each zone in gpm using the water meter and watering for a specific time (21 gallons in 2 minutes equals 10.5 GPM).
  2. Measure your total Area of the zone in square feet, and use 1/4 of that value for the side rows, and 1/2 of that value for the center row.
  3. Calculate Nozzle Inches per Hour = GPM / Area x 96.25.

Yes, there is substantial overlap of the spray heads, and you want that, but in effect, the center row has to provide half the total water to the zone in order to water most evenly. If the same spray head and adjustment is used in all locations, I would expect the center row Nozzle Inches per Hour to be roughly half of what the side rows are.

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