Projected Flow versus Actual Flow

Posted by Craig Zellers / John Hamilton

Why this is important to you and your Golf Course

When Golf Irrigation Consultants conducts a water audit and water use study, we pay close attention to what the irrigation central projected flow (toro) is compared to the actual flow. Projected flow is the total flow that the central computer calculates to run during the nightly cycle. In the Rain Bird central this is known as the “Dry Run”. The actual flow is what is measured from a flow meter installed at the pump station. Knowing the differential and correcting for discrepancies is crucial to the overall efficiency of your irrigation system.  

When we program a central computer, our goal is to be within 5% of these two figures. The perfect scenario for efficiency would be 100%, where the projected flow matches exactly what the actual flow is. Unfortunately we do not live in a perfect irrigation world where valves shut down in a timely manner and there are no leaks in the hydraulics or the sprinklers. From our experience, we have found variances of between 7% and up to as high as 48%.  We find that 80% of the time the actual flow is higher than projected.

When the actual flow exceeds the central projected flow, many irrigation systems will operate in a low pressure environment, often for many hours throughout the nightly irrigation cycle. Low pressures often lead to a golf course having increased wet spots and dry spots. You may also see the “donut” patterns around Irrigation heads. With increased dry spots, irrigation managers resort to increasing cycle times, or increased hand watering and hose dragging to compensate for the deficit. More often than not, when an irrigation system is operating under a low pressure environment, more water will be required to keep the course in a healthy and playable condition. These practices are merely treating the symptom and not the cause which wastes time, power, money and most importantly water! 

Low Operating Pressure Sprinkler

Factors which can be attributed to variances include:

  • Incorrect  sprinkler data programmed in the central
  • Leaking sprinklers, valves, hydraulic piping or fittings
  • Worn nozzles
  • Sprinklers added or changed after the initial installation and programming.
  • Slow closing valves
  • Faulty pressure regulation valves (PRV’s) or pilot valves
  • Landscape satellites installed and running in “stand alone” mode with no communication to the central.  (clubhouse satellites are an example)

In the following audits and water usage studies we found the following:

Course 'A'

Projected Flow:   439,000 gallons
Actual Flow:        510,000 gallons
Discrepancy:       71,000 gallons 
Variance:             16%

On course ‘A’ the variance was caused by an extremely large quantity of older leaking sprinklers and incorrect sprinkler and nozzle data in the central. On the higher elevations of the course pressure was very low during the nightly cycle.

Course 'B'

Projected Flow:   796,850 gallons
Actual Flow:     1,182,000 gallons
Discrepancy      385,150 gallons
Variance             48%

On course “B” there was many factors contributing to the large variance. The course added additional landscaping around the clubhouse, tennis courts and pool. Five controllers not connected to the central accounted for 55,000 gallons.  On the front nine housing had been added and an additional 11 acres of turf was installed and irrigated. Although the added stations were connected to the golf course satellites, they had never been correctly entered into the central database. These stations accounted for an estimated 35,000 extra gallons being pumped.  

In the central all sprinklers were programmed at 24 GPM. According to manufacturer nozzle charts the Toro 735 set with 65 PSI regulators should deliver 27.4 GPM. However; the sprinklers were retrofitted with an additional third nozzle that added 4 GPM.  We expected these sprinklers to distribute 31.4 GPM but in flow tests we discovered the number was close to 40 GPM.  Once all three of these variances were accounted for in the central, turf conditions improved dramatically.

Course 'C'

Projected Flow   522,900 gallons
Actual Flow        560,900 gallons
Discrepancy       38,000 gallons
Variance             7%

On course ‘C’ the variance is not too concerning but given that the system was only two years old, we expected the variance to be less. After further testing we determined that the flow rates per sprinkler were higher than what was programmed in the central.

Low Operating Pressure BeforeOptimal Operating Pressure 







In conclusion, we point out that variance tests are not difficult to conduct and every golf course should be aware of the effect that a higher variance can have on course conditions.   We can all agree on these three things;

1.  The demand for better more consistent playing conditions is a factor every  
     Superintendent must deal with and it will always increase, not decrease.
2.  The costs for water, power and labor make up a majority of every course budget and these too, will only increase and never decrease 
3.  Improving the efficiency of your irrigation system can only be beneficial! 

If you have questions or need help with these tests, call Golf Irrigation Consultants.

Cell: (415) 342-1030