The lid of the unit acts as a funnel, directing rainwater down into a smaller tube housed within the larger 8-inch diameter unit. When this smaller tube is filled, the larger outer container acts as a reservoir, catching the overflow without spilling a drop for later measurement.
The inner collection tube is 1/10 the diameter of the funnel to match the kiln measuring stick’s measured increments. One inch of rain water will fill the inner tube ten inches. Each inch on the kiln measuring stick equals 1/10th of an inch, so ten 1/10s inches is equal to one inch.
The gauge is held in place by a cylindrical steel frame set in concrete by bolts. These bolts can be adjusted to level the rain gauge. It is imperative that the gauge be perfectly level and away from any vertical obstructions such as trees and buildings. A good rule of thumb is to set your gage up so that it is twice the distance of a vertical obstructions height. So if you are setting up your gauge near a tree that is 50 feet tall, your gauge should be set up 100 feet away.
A kiln measuring stick–shown leaning against the gauge in the photo above right–is carefully lowered into the orifice at the top of the gauge until it touches bottom. When removed, the water level wets stick at a readable depth. This depth is the amount of rainfall recorded. Sometimes more than one stick is required to record the total rainfall. Having more than one stick is necessary when rainwater overflows from the smaller inner cylinder into the larger outer cylinder.
During these circumstances, the observer would first measure rainwater by gently and carefully lowering the kiln stick down into the smaller collection tube, then taking his or her reading. Next, the observer carefully removes the inner collection tube, being careful to allow any drops of water on the outside part of the bottom portion of the tube to drop back into the larger outer collection tube. Dump the water out of the small collection tube just removed, allowing every drop to come out. Then carefully set the smaller tube on a flat level surface and place the funnel lid securely onto it. It is best to have a helper to support the smaller tube with the funnel lid on it as it will be top heavy and unstable, particularly when you fill it.
Next take the larger outer collection reservoir with the overflow water in it, and carefully fill the smaller collection tube by pouring the water slowly into the funnel lid. Once you have removed every drop, take a new unused kiln stick (as the old one will still have the “stain” of the water level on it) and slowly and carefully lower it into the small collection tube as you did with the first kiln stick. Take the measurement and add this to the original measurement. If more water remains in the large collection tube, then empty the smaller tube out and repeat the steps you took to refill the smaller tube, using a third (and fourth etc) fresh unused kiln stick for each measurement; adding the totals as you go. The sum of all measurements is the total rainfall. Totally awesome!
The photo above shows the smaller collector tube inside the larger outer overflow catch tube.
It is best to use whitewash to reflect sunlight off the rain gauge to minimize the effects of solar heating and potential evaporation of the rainwater inside.
~ Steve Woodruff and Devin Lussier