Site information includes a sketch of the area where the cans will be placed showing the sprinklers or dip lines. Use the data sheet and map introduced previously. Dimensions must be shown. Use a measuring tape for all measurements and a ruler or protractor for drawing a sketch. Collection can placement is the next challenge to decide. First, the more catch cans one uses the better the data likely will be. Twenty-four or more cans are recommended to have on hand; the larger number of samples makes the results better statistically.
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If the sprinklers are spaced on a 30- by 40-foot spacing, the distance between cans should not exceed about 10 feet, the smaller the separation the better. More data points is better for producing more accurate results. Spacing containers at 10 foot intervals means 20 containers (Figure 4.3a). Spacing the containers at 5 foot spacing means 63 containers. Try the wider spacing of 20 containers first. Make a grid of rows so cans are equally spaced across and equally spaced lengthwise in the area.
Figure 4.3a. Sprinklers on 30 foot by 40 foot spacing with 20 catch cans to collect water samples. Cans next to sprinklers are a couple feet from sprinkler. Cans are placed one to two feet from the sprinkler head. Use a uniform placement pattern. |
Figure 4.3a |
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The above figure assumes a buried lateral line. If there is a lateral or main line to work around, the first catch can is placed on a two foot offset from the lateral and a couple of feet from the sprinkler head. Using a measuring tape, divide the space between sprinkler heads into rows going across between laterals and also parallel to the laterals. At least 20 – 24 catch cans should be used at a minimum. More cans give greater accuracy and more detailed data on water distribution. Remember, 10-foot spacing is about the maximum can separation for small sprinkler spacing. |
Locations for catch cans should be marked with a flag during the layout task. When one is satisfied with the locations, they should be marked on the sketch or map of the site. Use a circle to represent the sprinkler heads and an “X” or filled in circle or dot to represent the catch cans. Or, vice versa, just label each once so the symbols are known. Later when the data is being collected on the volume of water in each catch can, the measured volume may be written in on the site map. Figure 4.3b illustrates placing the catch cans on the ground in a regular pattern. Note that the catch cans need to be level and may require digging in the can so it sets level and below the sprinkler throw.
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Figure 4.3b. Catch cans are laid out in a uniform pattern. Note that the cans must be level and perhaps recessed into the ground. Nozzle spray must not hit the sides of the can.
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When all equipment is in place and the water pressure is correct, start the irrigation system and the stop watch. Run the irrigation system for the appropriate amount of time. Remember to record the wind speed and direction each five minutes. Note any problems with the sprinkler pattern or discharge pattern that is seen. Check the pressures again. When the application time is finished, stop the irrigation system and the stop watch. Note the stop time on the record sheet. Record the final water meter reading. Check the data sheet to see that all measurements have been done.
Measure the water in each catch can by pouring the water into the graduated cylinder, read the volume of water carefully, and record the volume next to the correct sprinkler on the diagram and in the correct space on the data sheet. Use the appropriate size graduated cylinder for measurements. |
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Figure 4.3c illustrates another catch can layout with the water measurements shown in inches of water depth. Here 16 catch cans are used; it is suggested that multiples of 4 be used for number of catch cans to make later calculations easier.
As a permanent record or backup, the data should also be entered into a table based on the placement grid. The purpose of recording the data on the site map is to be able to come back later to locate the places that are over-irrigated or under-irrigated. That in turn will help in finding specific steps for making improvements in the system’s performance.
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Figure 4.3c. Another catch can layout with equal land area per sprinkler but fewer cans. Cans are placed at a 2 foot offset of the laterals. Water measurements are shown next to cans as an example. (Source: http://edis.ifas.ufl.edu/images/1007002252, Univ. of Fl – IFAS Bulletin 266, Dec. 2005).
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