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:
- 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).
- 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.
- 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.