Run the sprinkler system for 30 minutes.
Measure the amount of water collected in your watering gauge, pan, or shallow can.
Multiply that depth by 2 to get the amount of water that your sprinkler applies over a one hour period.
Adjust the flow rate and running time of the sprinkler to apply the amount of water intended without causing runoff.
For example, your sprinklers ran for 30 minutes and you collected ¾” of water. Multiplying ¾” by 2 equals 1.5 inches over a one hour period. You thought you were applying ½” over 30 minutes, or 1” over a one-hour period.
Next time you irrigate, you can reduce the flow rate (gallons per minute) as needed to result in ½” over 30 minutes or 1” over a one-hour period. You can figure this out through trial and error. If the flow rate is set and not contributing to runoff problems then simply reduce the running time. For example, you could reduce the watering time to 20 minutes and then measure again to see if you are now at ½”.