4.1 Equipment Required

Catch cans are required to collect samples of water from many locations under an irrigation system. Typically, under an overhead sprinkler system, the cash cans are placed in a grid under a pattern of four sprinklers. For drip irrigation systems, catch cans are placed under individual drippers to collect the samples. Below is a list of equipment of equipment to consider having ready to do an audit study. Figure 4.1a shows a few of these items that can be purchased for this purpose.

The equipment that would be most useful for the study includes:

• Notebook of documents and record sheets

• Two clipboards (or one per group)

• Packets of graph paper or engineering paper

• 24 to100 catch containers – straight sided cans, tapered containers

• Bundle of flags on wires to mark can locations

• Two Plastic graduated cylinders for reading the water collected; cylinders of 100 ml, 200 ml and 500ml seem to be suitable sizes.

• Two stop watches

• One magnetic compass

• Small weather station such as Brunton ADC Summit weather station or anemometer

• Two 100-foot measuring tape

• Two 25-ft or 30-ft measuring tapes

• Wire flags to mark locations

• A pressure gauge with pitot tube and sill cock adapter

• Map of site on which to make notes.

• Two straight edge rulers

• Two protractors or triangle sets

• Digital camera

• Pipe wrench

• Adjustable wrench

• Screw driver

Any of a variety of containers will work for catch cans but there are some things to take into account when selecting the containers:

• The opening should be not less than 2 inches in diameter or 3 square inches in area. Small opening containers take too long to fill and do not provide a very reliable sample of precipitation.

• Containers with parallel vertical sides will allow one to measure the water depth directly with a thin ruler inserted into the container. One disadvantage is that the containers do not stack for storage or transport.

• Unbreakable plastic containers are better than glass. Metal ones may rust.

• The container’s base should be large enough that the container does accidentally not tip-over during the test.

• If the cost is not prohibitive, one can buy conical, graduated catch cans equipped with metal supports.

• Square catch cans with tapered sides may be stable on the ground and stackable. Pouring the collected water into a graduated cylinder to measure the precipitate volume may be easier and more accurate that using a ruler to measure depth.
  

The catch can illustrated here meets many of these requirements (Figure 4.1b).

The measuring container into which the water is poured from the catch can must have good volume markings so it is easy to read the volume of water. A measuring container that is tapered at the bottom makes it easy to read small volumes. It also must be large enough to measure the volume in one pour. Figure 4.1c illustrates one container that can be used.

An example of depth in inches will appear later. The container can be calibrated like a rain gauge and can be tapered. Reading the container is best done by one person for all catch cans so all readings are done the same. Holding the container level is important.