View Full Version : Rain gauge question
08-20-2009, 10:41 AM
A coworker and I were talking about the amount of rain we have picked up this past week. I mentioned we got about a 1 inch this past Sunday and another 1.75 inches yesterday. He said he believes he got more but did not actually measure it. I asked what he was talking when he said he did not measure it and he said when itís supposed to rain he just puts a 5 gallon bucket on his patio and then grabs a tape measure if he really wants to know how much they got. Sounds logical to me. BUT then as we continued to talk I mentioned I have a high tech rain gauge http://www.johndee.com/discuss/clipart/happy.gifthat is about 2 inch in diameter made out of clear PVC. It has a red float and increments on the side, so I can just look out the window and see how much rain we got. But on the top of the PVC there is a cone shaped piece added and I am guessing the opening is about 4Ē then tapers down to the 2 inch. So my coworker said my rain gauge is collecting twice the amount of rain falling from the sky then his bucket. I stopped and thought about it and ya he is correct, but yet the rain gauge it store bought so the manufacture must have somewhat of an idea what they are doing. Can anyone explain why my rain gauge has a larger opening then the measuring part?
08-20-2009, 10:50 AM
The rain gauge you have has the funnel on the top and the smaller diameter tube on the inside to help make it easier to read the fractions of an inch of rain. I have a similar one that when the inner tube is filled, it is exactly 1" of rain. So if the inner tube is not filled, it is very easy to measure the 10ths of an inch of rain that falls. Once the inner tube fills, it spills out into the outer tube, so you still get all the rain collected. If the inner tube is full, you just dump it out and then pour the water from the outer tube into the inner tube to measure the 10ths of an inch more rain you got. The whole system will collect up to 11". If you get more than that in a single event, you have bigger fish to fry than wanting to know exactly how much rain fell!
By the way, your coworker's way of doing it is just fine as long as the sides of the bucket are not tapered in any way. I believe 5 gallon buckets are tapered slightly though as you can nestle one inside the other a bit. Probably not too much, so their measurements are in the ballpark.
08-20-2009, 11:53 AM
To add to John's response the indications for 1", 2" etc are not spaced one inch apart, they are spaced further apart to accommodate the larger collection funnel.
08-20-2009, 01:13 PM
Scott b.....I think you just hit the nail on the head! I never thought about that, even though I look at the darn thing all the time!
thanks John and Scott for the answers
08-21-2009, 10:17 AM
Get out your straight walled...anything (sos-long as the deemensions are same as that of the opening of that Gauge), pour some water in to a known inch mark (put some red food coloring in...very important ingreediant) and cross check what is there.
My bet is that these were made in China, and they were thinkin in metric but scribing in inches.
Jist kidd'n, you can see how well they did by your own use of some elementary science stuff....you did take science...eh?
08-22-2009, 09:38 AM
We have a number of rain guages around the yard. It always surprises me how different two will read, sitting right beside each other. The weather station guage has a little rocker/dumper that gives a reading on every .04inch increment.
We also have one that measures in volume (liters per square meter). That guage would be maxed out with a good two inch rainfall.
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