This article will show the superintendent how to adjust sprinkler run times based on the variation in the amount of water that actually reaches the turf.

APPLICATION EFFICIENCY
Application efficiency is basically an analysis of how evenly the sprinkler system outputs water in the field. The more variable the application of water is from spot to spot, the greater the potential there will be for both wet and dry spots occurring on the golf course.

Application efficiency determines to what degree the normal operating run time needs to be adjusted to, in order to compensate for the variation of sprinkler output in the field. Here we are talking about more than one sprinkler operating at one time in the field test itself.

An annual season "tune-up" is necessary before field testing can be implemented. A tune-up and evaluation of the system includes examining often overlooked items which can greatly effect the efficiency of the application.

Such items should include:

* Checking heads for alignment (heads should be raised or lowered and be level or perpendicular to the ground slope for flat and slightly sloped areas only).

* Check nozzles for wear, broken pieces or clogging.

* Verify operating pressure at the nozzle for nozzle/spacing combination.

* Verify if the sprinklers have matched precipitation rates if they are operated from a common valve.

Assuming the irrigation tune-up is complete, nozzles have been checked for IPH rating and operating pressure and heads checked for rotation speed, it's time to place catch cans in the field.

PLACEMENT OF CATCH CANS
Catch can devices are commercially available which allow for easy measurement and recording of the water collected in each can. The best ones are conical in shape and have grade marks on the side of the funnel which have units in either millimeters of water (mm) or fractions of inches. These devises come with steel holders which are inserted into the turf. The holders adequately prevent the cups from tipping sideways, which would provide false readings.

HOW MANY AND WHERE
In general, catch cans should be placed along lateral lines in full circle stations and should be offset slightly from edges of part circle stations. For square spacing areas (greens, tees or other areas where used) place one catch can within 5-8 feet of each sprinkler itself. Then, place one catch can halfway between itself and every other sprinkler which contributes, in head-to-head coverage. So for square spacing, the minimum number of catch cans required would be 2 for each head. One 5-8 feet away from each head and one half way between. For four sprinklers in a square spacing arrangement, a minimum of 9 catch cans should be used. Note that the placement of the one can closer to the head can be in either of two locations (at either one of the two 90 lines between the other two sprinklers in the square spacing). This would be the minimum requirement (9 catch cans). Alternatively, four rows of three cans each can be used.

For triangular spacings (commonly used on fairways), the same general rules apply. Locate one can 6-8 feet anywhere within the radius of the sprinkler. Place another catch can midway between the same sprinkler and any other sprinkler that contributes to its head-to-head coverage and vice versus. An extra catch can devise between each set of heads (in the middle of the triangle is acceptable and recommended). For details on more elaborate spacings for single sprinkler profiles and field evaluations, see references of Kah and Vermuellen.

A simple grid pattern can be used for irregular shaped areas which are odd shaped and have a mixture of spacing arrangements. This assumes that the test area is on a single station, or will be operated as one.

RUNNING THE TEST
The next operation is to run the sprinkler system for 30 minutes, making sure that any full circle heads complete at least 5 full rotations. Run multiple stations if possible for multi-station controllers, but don't exceed the capacity of the laterals to deliver the gpm at the specified pressure at the head(s). Remember that laterals that contribute to the overall application in the triangle spacing must run for the same amount of time as the other laterals that contribute to the area being evaluated.

After the system has stopped, measure the amount of water in the catch can. Hold the cup level and read the amount of water collected to a partner, who records it on a data sheet. Since the irrigation system ran for 30 minutes, you need to multiply the reading by 2, so the information will be in units of inches per hour.

If its raining (and not windy) you can simply subtract the rain amount from each catch can devise to get the precipitation rate applied to each can. The rain can is simply placed in the open turf away from trees and does not receive irrigation water. In fact, rainy days may be convenient to perform a catch can test, since most other routine tasks may not be possible.

A LOOK AT THE CATCH CAN DATA
Looking at the catch can data sheet, two important pieces of information should catch your eye immediately. First, do the numbers recorded vary tremendously (its best if they are close to one another) and secondly, are there one or two numbers which drastically stick out as having high or low values? This information will allow you to adjust your systems irrigation based on these results and the degree of turf quality you as the superintendent are expected to maintain.

After the data has been recorded from the field (columns 1 of worksheet), the second step is to rank the catch can amounts from low to high (column 2).

Note that there is a two fold difference between the lowest can (0.39 inch) versus the highest can (0.87 inch). It is important to attempt to find out what is causing these two extremes. Is it caused from improper head spacing, improper or worn nozzles, insufficient pressure at one or more heads, or nozzles which are not matched for precipitation rates?

Compute the mean precipitation by summing the depth of water in all cans and dividing it by the number of cans. Our example has a mean precipitation rate of 0.62 inches per hour (7.44"/12 cans = 0.62"). The mean precipitation rate will be used to adjust the irrigation system based on the degree of turf quality desired. We will now devise three scheduling coefficients, which simply stated, are three multipliers used to adjust normal run times (based on the mean precipitation rate of 0.62 inches per hour). Below are three examples of how to calculate different multipliers (scheduling coefficients), based on our sample data, and examples where they would be used.

FIND THE BASE RUN TIME
It is desired by the superintendent to irrigate a fairway with 0.30 inches of water. Given the mean precipitation rate of 0.62 inches per hour, we calculate a sprinkler run time of 29 minutes. (0.30" desired/0.62" precipitation) X 60 minutes gives us our 29 minutes. If we ran the system for 29 minutes, the driest catch can area would be under irrigated by 37%. This may or not be acceptable, depending on the turf quality desired and the dependency on supplemental irrigation to keep the turf green (no rainfall).

OPTION 1. S.C. -- Scheduling coefficient
This adjustment is a numerical value which is calculated by dividing the mean precipitation rate by the single driest catch can. From our example:

S.C. = 0.62 inch (mean) = 1.59

0.39 inch (driest area)

The S.C. of 1.59 is used as a multiplier to adjust the base run time of 29 minutes. The new adjusted run time, based on a S.C. of 1.59 is simply calculated as follows:

29 minutes base time X S.C. of 1.59 = 46 minutes.

The larger the S.C. adjustment, the longer the irrigation system must run. The S.C. is the most severe case adjustment, since we are adjusting the irrigation to cover the single most driest spot! Other areas will be overwatered, but at least the superintendent knows how much each collection area is either over or underwatered. The S.C. factor can be used on the highest priority areas such as greens and tees, where turf quality and performance needs are maximum, and loss of turf from under irrigation is not acceptable.

OPTION 2. -- Distribution Uniformity -- D.U.
The D.U. is the second run-time multiplier option the superintendent can use based on catch can analysis data. The simple task here is to adjust the irrigation system base run time by taking into consideration the lowest 25% of the catch cans. Previously with the S.C., we used the single driest can only. From the worksheet, write down the precipitation rates for the driest 3 cans (25% of 12). These are 0.39", 0.51" and 0.54" located in column 4. The total sum precipitation of these three cans is 1.44, and the mean of these cans is (1.44/3 cans) = 0.48 inches.

D.U. = 0.62" (mean of all cans) = 1.29

0.48" (mean of lowest 25%)

Thus we have a D.U. multiplier of 1.29.

To find the proper run times, let's do the following:

29 minutes base run time X D.U. of 1.29 = 38 minutes.

Thus you can see that the D.U. applies less water overall than the S.C. For most cases, the D.U. can be used suitably for maintaining turf at moderate maintenance levels, such as fairways and other medium profile areas.

OPTION 3. -- Midpoint Uniformity -- M.U.
The midpoint uniformity is a third option and as you will see, the M.U. is the most conservative adjustment of the three scheduling coefficients used.

To compute the M.U. adjustment factor, transcribe to column five of the worksheet, the lowest 50% of the catch can data (.39", .51", .54", .56", .57" and .61").

The total of these six cans is 3.18", and the mean of these six cans is (3.18"/6) 0.53 inches.

The M.U. is calculated as follows:

0.62 (mean of all cans) = 1.17

0.53 (mean of lowest 50%)

Thus our M.U. multiplier is 1.17.

To use this new multiplier, simply multiply the base run time by the M.U. value.

29 minutes base run time X M.U. of 1.17 = 34 minutes.

Thus you can see that the M.U. is more conservative than the S.C. and D.U. for irrigation purposes. The M.U. can be used to irrigate lower maintenance turf with lesser quality expectations than turfs which are irrigated with either of the other two adjustment factors.

The M.U. will under irrigate more areas than the D.U. therefore, it is suitable for golf course roughs, out of play areas, and other low profile areas.

Looking back at our examples, the operating run times needed to apply 0.30 inches of water using the three different scheduling coefficient run-time adjustment factors are a follows:

METHOD SYMBOL VALUE RUN TIME
Base run time Base --- 29 minutes

Scheduling coefficient S.C. 1.59 46 minutes

Distribution Uniformity D.U. 1.29 38 minutes

Midpoint Uniformity M.U. 1.17 34 minutes

Once again, to calculate the base run time, use the formula (water replacement value/mean precipitation rate) X 60 minutes.

Select the proper adjustment factor (S.C., D.U. or M.U.). Then multiply the base run time with the selected adjustment factor to determine the final run time in minutes.

The number of catch cans placed in the field depends on how accurate you want to be on a specific type of irrigation condition, or how many conditions (locations, different types of sprinkler makes, models, spacings) you may have on the golf course. The back nine might have been constructed at a different time with different irrigation equipment than the front nine. Partial retrofit areas need separate investigation as well.

For the same fairways which have the same spacings, nozzles and head combinations, you may want to concentrate by placing more cans on one fairway and using this information for systems adjustment for areas which have the same hardware. (see reference of Kah)

If the golf course has several areas which differ greatly, the superintendent can place the minimum number of cans as proposed and use the site specific information for each area only. Either way, you will have a better understanding of actual irrigation precipitation in the field, and have the capability to adjust accordingly depending on turf quality expectations.

Note that different terms may be found in the literature regarding the specific names of scheduling coefficients (run time adjustment factors). Also, the method of determination may be different. Given the same exact data, slightly different values of scheduling coefficients may result. The methods and example used here show how to calculate three run time adjustment factors and options on where to use them.

1. Kah, Gary and W.C. Willig. "Does Your Course Measure Up." Golf Course Irrigation. Jan/Feb 1994. (pp18-21).

2. Vermuellen, Paul. "Rain Making." USGA Green Section Record. March/April 1994. (pp8-10).

3. Solomon, K.H. "Irrigation Efficiency". GCSAA One Day Workshop. (pp1-205).

4. Kopec, D.M. and C. Throssell. "Irrigation Scheduling Techniques." GCSAA One Day Seminar. (pp1-126).

 Figure 1.
 

Placement of 12 catch cans within a golf course green. Diamonds represent sprinkler heads in a square spacing design. Note that two lateral lines are used in this example.
 
Figure 2.
 

Placement of catch cans in a fairway. Note that three lateral lines are used in this example. Diamonds represent sprinkler heads in a triangular spacing.