By Michael D. Vogt, CGCS, CGIA
Unlike an IRS audit, an irrigation audit can be very beneficial in golf course water savings, power savings, irrigation equipment longevity and result in better all-around turf conditions.
It’s impossible to see where all the water goes after it leaves the sprinkler head and to what degree distribution uniformity is achieved. A well designed and maintained watering system will deliver a uniformed amount of water throughout its irrigation pattern, thus eliminating wet and dry spots. However, even the best sprinkler / nozzle combinations fall short of perfect uniformity. Watering systems with poor uniformity must apply greater volumes of water to an area to achieve the same results as a system with good uniformity, most often resulting in a wet golf course. Sprinklers typically used on golf courses fall into three categories as identified by the Irrigation Association’s Certified Golf Irrigation Auditors manual, these are:
• 70% distribution uniformity (good, expected)
• 55% distribution uniformity (poor)
Golf Course Irrigation System Audits
More golf courses are deciding to perform audits to discover how much and where water is being applied to the course. An irrigation audit is a thorough analysis of the operation of this complex system of water delivery on modern golf courses; a comprehensive audit covers the following:
• Water Supply • Pumping system(s) • Piping system
• Pipe fittings • Valves • Sprinklers
• Control system • Management practices • Water distribution audit
Irrigation audits are very effective in documenting irrigation system efficiencies and a well written report can be an excellent tool for communications to members, Board of Directors, committee members and owners to better understand one of the superintendent’s most important and complex tools. Members and owners seldom see the irrigation system; an audit will help them understand the significant investment, maintenance expense and operational cost of one of the largest, complex systems on the course.
Distribution Uniformity
As mentioned earlier, distribution uniformity (DU) is a critical measure of the irrigation systems ability to apply water uniformly to the turfgrass. A value of 100% represents perfectly unformed coverage of water to a predetermined area; however, perfect uniformity never occurs, even with rainfall.
For golf course irrigation audits, DU is generally calculated by identifying the volume of water that is applied to the driest 25% of the test area and dividing it by the average volume throughout the test area. This is also expressed as the Lower-Quarter Distribution Uniformity or DULQ.
DULQ is an important component of the audit and points out the areas of low efficiency in order for a plan to be formulated and begin to address irrigation system flaws, saving water, power and improving playing conditions and turf health through dryer surfaces.
DULQ is calculated though the use of catchments (collection devices), each catchment that is used in the test must have the same opening area or “throat” and must be stable enough that it can not be relocated or knocked down by operating sprinklers. The proper placement of catchment devices is critical in conducting a water distribution audit. The catchments should be placed in a grid throughout the entire target audit area.
The System Check
Before the catchments are place for the DU test a simple system check is required, these checks include:
Sprinkler check: an activation of each sprinkler in the test zone to inspect and correct any tall grass around the sprinkler. Level and free of physical damage that needs attention.
Nozzle check: make sure proper nozzles are used. Also be certain that nozzles are not cracked broken or otherwise distorded.
Conditions Check: The audit should be conducted under normal system operating conditions. Normal irrigation run times are in the evening when wind conditions are less pronounced, as a rule audits should not be performed with wind conditions that exceed 5 mph. Document: Sketch a map of the zone to be tested, use an existing drawing if available. Show all sprinklers, nozzle type, rotation arc, model number, operating pressure and pairings if wired to operate together with other sprinklers.
Lay Out the Catchments, Begin DU Test
After the above system test the actual DU catchment test can be performed. The catchment devices should be place in a grid sequence 12 to 15 feet apart.
Run sprinklers in a normal sequence that would simulate an irrigation event for the unique zone being examined. The minimum time prescribed for the DU test is 15 minutes so that the catchments can accumulate a sufficient amount of water for measuring. All sprinklers in the test zone should run for an identical period of time.
Record the volumes on the site map of each catchment and perform the calculations. DULQ can be calculated by the average volume of the lower one quarter of catchments times one hundred divided by the total average of catchments or:
DULQ = Average of Lower Quarter Catchments x 100
Average of all Catchments
Remember:Average of all Catchments
• 80% distribution uniformity (excellent, achievable)
• 70% distribution uniformity (good, expected)
• 55% distribution uniformity (poor)
What Does DULQ Really Mean?
DULQ is a percentage that can be calculated into what is referred to as a Run Time Multiplier. This number factor in a given value that indicates you must run your tested portion of the irrigation system a multiple of X to get proper coverage in the driest spots.
These are the Run-Time Multiplier conversions:
Run-Time Multiplier, How is it Significant?
Run-Time Multiplier (RTM) is a calculation used to determine the number of additional minutes sprinklers must run to ensure the driest areas in the sprinkler’s coverage area receives adequate water.
Using the table above, it’s plain to see how areas with poor DU would require more water. An area with a DULQ of 68% would require 24% more water to achieve ideal coverage. Thus, a system improvement of 12 DULQ would yield a RTM of 1.14 or an overall efficiency increase of 10%. That might not seem like much, but take for example if your combine power and water use is $120,000 that would be an annual savings of $12,000. That does not include longevity on pump station run time which could easily be one addition year of service amortized over the life of the station cost, in most cases at least $10,000.
Real Life Precipitation Rate Calculation
The above catchment data can also be used to arrive at the average precipitation rate. The precipitation (PR) rate is expressed in inches per hour in the USA.
PR= Catchment Volume Average (in milliliters) x 3.66
Test Run Time x Catchment Device Area (throat area in square inches)
Once you have determined average PR, determining station run time is accomplished by multiplying a desired precipitation rate by 60 and dividing it by the PR. An example would be:
If a PR for a given area is 0.71 inches per hour, and a desired application rate is 0.2 inches per hour, the area should be programmed for 16.9 minutes.
0.2 inches per hour x 60 = 16.9 minutes
0.71
In addition to this calculation, if the area above had a Distribution Uniformity or DULQ of 64% the run-time multiplier can be used to determine the adjusted area run time.
16.9 minutes x 1.28 = 21.63 minutes
Thus, in the area audited it would require approximately 22 minutes to supply the area of turf 0.2 of an inch of water.
The Irrigation Audit Bottom Line
By auditing the irrigation system a superintendent can find additional savings in water, power, system life; an irrigation audit and a good irrigation system maintenance program always pays for itself.
Select only a Certified Golf Irrigation Auditor (CGIA); they know golf courses and the workings of a complex golf irrigation system. Also select an auditor that has no affiliation with a company that sells irrigation supplies, an auditor with no bias will insure a proper audit takes place without regard to further his or her business.
After the audit is performed map out an action plan based on recommendations from the CGIA, and let the local community know that the club is concerned with the areas water resources, concerned enough to keep water consumption to a minimum through careful management of water and additionally, the use of electric power.
The overall efficiency of the irrigation system is dependent on the golf superintendent’s devotion to protecting natural resources. The best operated and maintained irrigation system a superintendent can attain is end to that goal.
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