Irrigation Audit – Results and Conclusions
Fairway Country Club
Your Town, New York
May 12, 2009
Certified Golf Irrigation Auditor: Michael Vogt, CGCS, CGIA #58853
In order to locate problem areas on the course and evaluate equipment performance, I have performed a preliminary irrigation audit of the golf course irrigation system. The audit consisted of both, visual and mechanical inspections of the irrigation system.
Visual Inspection identifies problems such as poor head spacing, tree limbs, soil type, thatch, broken sprinklers, etc… and the Mechanical Inspection is an actual System
Performance Test using catch pans to evaluate sprinkler performance. The areas tested for the System Performance Test were on Holes 7, 11, and 14 fairways. Fairway areas were tested since these showed signs of poor irrigation coverage throughout the summer months. Results and recommended corrective actions from both the Visual and Mechanical Inspections are included.
One of the largest problems with the irrigation system is the lack of a “pump watch” cable, which sends real-time, pump flow data (GPM), to the irrigation computer. For the irrigation computer to calculate the number of heads the system can run at one time the irrigation computer must rely on a Precipitation Rate value (PR), which is manually entered into the irrigation software. i.e. 25 heads running at a PR of 30 GPM per head = 750 GPM of pump flow.
However, the pump station flow meter shows 740 GPM at the same time the irrigation computer shows 600 GPM. This inconsistency between actual pump station flow readings and the irrigation computers predicted flow calculation is evidence that the
Gross PR value entered into Nimbus is off by 20-30%.
When the system was designed and programmed many years ago, a value of 30
GPM/per head was used as the PR. This value is incorrect and is the primary reason for poor system performance. Also, since that time, many nozzles have been switched out with a higher flowing “double-tail” nozzle. Citing current Rainbird nozzle specifications, the actual flow of the nozzles is probably 33-39 GPM depending upon if the nozzle has a single or double-tail.
I have temporarily solved the problem by lowering the irrigation computers maximum flow to 600 GPM, or 20 heads, which gives a pump station flow reading of 740 GPM when the system is running at 100%. The drawback is that the lower maximum flow used for the irrigation computer means fewer heads can run at one time, and causes the irrigation cycle to be extended. During summer months, the system runs approx. 20 hours/day. This creates problems when trying to schedule irrigation cycles around the many golf tournaments each season.
Unfortunately, increasing the pump flow above 750 GPM is not an option. Since pump station flow above 750 GPM exceeds the carrying capacity the mainlines were designed for and will result in system pressure loss, poor coverage, and equipment failure, due to friction loss forces of the water moving through the pipes.
Friction loss forces caused by the distance from the pump station to the Upper holes are also one of the reasons why the irrigation cycle must run for 20 hours/day.
Visual Inspection (continued)
When the pump station flow exceeds 450 GPM pressure problems become apparent on the Holes 13,14 and 15. To solve this problem I have programmed separate irrigation cycles for the Upper and Lower holes. When running the Lower holes, the system will run at maximum flow, 750 GPM. Once the Upper holes begin to water, the system will stay below 450 GPM. This means that for half the night, you will be running the irrigation system at less than maximum output.
Isolating the Upper and Lower irrigation systems from each other would be the best way to solve the 20 hour-a-day irrigation cycles. If you could run both the upper and lower holes at the same time, you would cut your nightly run times in half, and minimize irrigation system runtime during daylight hours. Installing larger irrigation mainlines, and installing a new VFD pump, is one way to increase system flow above the 750 GPM it is currently designed for. Alternatives, would be to locate a booster pump at the Paseo
Street crossing, or build a 2nd pump station, using the lake on Hole 12 as it’s’ source.
This would allow you to run irrigation cycles on both the upper and lower holes concurrently.
Another problem needing corrective action is the levelness of the irrigation heads. I inspected all of the greens heads for levelness. Each green had several heads that need to be leveled. Several greens had heads that were 3 to 4 inches below grade. I recommend including an aggressive head-leveling program into the maintenance scheme, for the next several years. This is an important job, and all crew members should be properly trained to perform this task, before allowing them undertake it unsupervised. Repairing the greens heads should be a priority over the next year.
Areas of importance would be: greens 1st, then approaches, fairways, tees, perimeters, and rough last.
It has also come to my attention that the pressure regulators on the sprinkler heads for Hole 11 may have been adjusted fully open several years ago. I recommend purchasing a Pitot tube pressure gauge, and resetting the pressure regulators on Hole 11, and any other areas suspected of over pressure water loss. This is the first corrective action that should be taken since it is the least expensive and locating sources of water pressure loss is a priority. Holes 10, 6, and 5, would be adjusted next, since they sit at lower elevations than the rest of the course. Eventually, all heads on the course should be tested and have their pressure regulators set at the proper level.
Tree limbs are problematic throughout the course, but not a priority. Holes 13-16, 10,
11, 5, and 6 have the worst areas where tree limbs are causing poor irrigation coverage.
Thatch accumulation and soil compaction on many of the fairway areas is causing runoff and water waste. Specifically, the fairways on Holes 5, 7, 13 and 14 have up to 1.5 inches of thatch. Excess water must be applied to wet the thatch layer before water can move into the soil profile. This results in water runoff, shallow roots and increases irrigation run times. I have addressed the issue by creating “soak cycles” for certain fairway areas with excess thatch and areas where slopes can cause water runoff during/after the irrigation cycle.
Hole #7 is showing the worst signs of thatch accumulation. Sod in the fairways can be peeled up, since the roots don’t extend very deep into the soil. Another side effect of excess thatch seems to be an accumulation of salts just beneath the thatch layer.
I have provided an example in the following photos. Notice how the sod peeled up in an almost even layer just below the thatch layer. This is how shallow the roots are. The white salt nodules on the soil surface are very evident as well.
The typical treatment for thatch accumulation is aerification and/or verti-cutting. An alternative is the application of wetting agents to the problem areas. If you have noticed the large, dark green areas on #7 fairway, these are test areas where I applied a wetting agent several months ago. Although temporary and rather expensive, using a wetting agent to help water move past the thatch layer appears to be an option in increasing irrigation efficiency. Future testing of excessively thatched areas, using an infiltrometer, is recommended to document the thatch layers effect on water infiltration rate, and establishing soak cycles, for future irrigation programming. This could help shorten overall irrigation run-time as well, by eliminating run-off and water waste.
System Performance Test
System performance can be measured in what is termed Distribution Uniformity.
Distribution Uniformity is the "measure of how uniformly water is made available to the plants over an area. DU value is expressed as a percentage and generally represents the major component of irrigation efficiency". Specifically, I looked at the Lowest
Quarter DU, which is calculated by taking the lowest 1/4 of the catch pans' values from the irrigation audit as an average, and dividing them by the average for all the catch pan values. Most new irrigation systems are designed with a minimum DU value of 80% and several states have already mandated an 80% DU for all new systems. Having a high
DU (>80%) is a good PR tool, as it shows you are making efficient use of your water resources with documented results.
Precipitation Rate is the "rate at which irrigation water is applied per unit of time". For these tests I calculated Net PR, which takes into account the water losses that occur between the nozzle and the ground. As I mentioned before, you’re Rainbird Central
Computer has a PR value manually entered into it. This value represents the Gross PR, and does not take into account any water losses between the nozzle and the ground.
Gross PR represents the actual water flow out of each head.
Each test consisted of a before-and-after evaluation of Precipitation Rate (PR) and Distribution Uniformity (DU). The initial test (Audit 1) was an "as-is" test and the 2nd test (Audit 2) in each area was done after replacing the nozzles in each tested head with new nozzles. Initial results showed that the DU can be increased by 10% and PR can be made more uniform for the entire system, simply by replacing the old nozzles with new ones.
I used 25 catch pans in each audit area. 4 adjacent heads were used for the audit and run for approximately 16 minutes each.
Soil samples were also taken from each area to determine the soil "texture" classification. Combined with the PR value calculated from the audit, the soil texture information will be used when scheduling future irrigation run/soak cycles. I have attached copies of each Audit Worksheet for your inspection.
Test Results Summary: Run Time per DU PR (in/hr) head at 0.20ET
Hole #7 Audit 1 – Green 66% 0.54 32 sand
Audit 2 – Green 75% 0.47 32
Hole #11 Audit 1 – Tee 69% 0.51 33 loamy sand
Audit 2 – Tee 82% 0.44 31
Hole #14 Audit 1 – Green 70% 0.41 40 sand
Audit 2 – Green 77% 0.41 37
As you can see from the results, I obtained an average DU increase of 10% each audit area. The interesting thing was that, the PR went down considerably on both holes 7 and 11, simply by replacing nozzles, and at the same time, the irrigation run-time went down by several minutes on Holes 11 and 14. This shows the value of increasing DU, since even though the PR went down, the irrigation efficiency was increased enough to lower overall run times for the sprinkler heads.
Pressure problems are the primary cause of poor irrigation system performance on the upper Holes 12-16. By making changes to the irrigation schedule, the pressure problems can be overcome, but also create a new problem, a 20 hour watering cycle during peak watering periods. So now, in order to reduce the length of time we are watering each night, we must increase the efficiency, or DU, of the irrigation system.
Many of the fairways on the course show symptoms consistent with the areas I tested for this initial irrigation audit. My opinion is that, if we were to replace the nozzles in these problematic areas with new ones, we could save several hours of irrigation time each cycle. Further increases in DU, could be achieved by beginning an in-house head leveling program, or perhaps contracting the work out to a 3rd party.
My recommendations for increasing the efficiency, or DU, of the irrigation system are:
In order of priority:
1. Adjust pressure regulators on sprinkler heads.
2. Replace nozzles in problem areas.
3. Intensive head-leveling program.
Turfgrass cultural recommendations are:
1. Continue aggressive turfgrass cultural program on fairways (aerification and verticutting).
2. Use of wetting agents on problem areas could be an alternative, when aerification is not possible.
3. Refine irrigation schedules, by using an infiltrometer, to establish soak cycle lengths required during irrigation schedules.
Future capital improvement projects and long-range planning should include:
1. Installation of an irrigation computer-to-pump station, “pump watch” cable.
2. Separation the Upper and Lower irrigation systems, by installing 2nd pump station on
Hole 12 lake, or install a booster pump on the section of mainline crossing Smith Road.
I also recommend, performing further irrigation audits on the greens next spring.
Getting a better idea of the actual PR for the greens, would allow more precise programming of the irrigation schedules. This could help to eliminate many man-hours dedicated to hand water the greens during warm periods.
Michael Vogt, CGCS, CGIA #58853