Public Lab Research note


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Measuring water in a rain gauge

by stevie |

Lead image from commons.wikimedia.org

The purpose of this activity is to document how to use a rain gauge to collect information on rainfall.

While you can use a gauge to document other types of precipitation, this activity will walk through how to take a water measurement from a rain gauge that has already been put up. For more information on installing your rain gauge, measuring other forms of precipitation, or documenting your data on a data map, visit the CoCoRaHS website here.

"CoCoRaHS is an acronym for the Community Collaborative Rain, Hail and Snow Network. CoCoRaHS is a unique, non-profit, community-based network of volunteers of all ages and backgrounds working together to measure and map precipitation (rain, hail and snow). By using low-cost measurement tools, stressing training and education, and utilizing an interactive Web-site, our aim is to provide the highest quality data for natural resource, education and research applications. We are now in all fifty states." (CoCoRaHAS.org)

Materials Needed:

  • A rain gauge
  • A writing utensil
  • A form for documenting the results (example from CoCORaHS here)
  • A post for putting the gauge up to their specifications (see this resource for information on putting up your gauge)
  • Spare bucket (you will use this if it has rained over an inch since your last measurement).

Video tutorial

Watch this video (1min-2:37) to help you visualize the steps below.

Naming the pieces of the rain gauge:

  • The Lid: the top of the rain gauge that is an inverted cone shaped
  • The measuring tube: the smaller cylinder inside your rain gauge. this piece comes out and has measuring units on it in 0.00inches up to an inch)
  • The outer cylinder: this is the larger outside piece of the rain gauge. The smaller cylinder sits in this. It catches the water from the smaller cylinder if it rains over one inch.

Collecting your CoCoRaHS data

Once you have put your rain gauge up, you can start collecting your daily rain data.

An inch or less of rain:

If it has rained less than one inch since you've last collected the your rain data, there will be no water in the outer cylinder of your rain gauge.

  1. Remove the measuring tube of the rain gauge by taking off the lid and reaching into outer cylinder.
  2. Check to see if there is any water in the gauge itself.
  3. If there is no water, record 0.0 on your data sheet and return the measuring tube to the rain gauge and set it up to collect rain again.
  4. If there is water in the measuring tube, record the amount of water in the tube to the nearest hundredth of an inch. (0.00in)

More than an inch of rain:

If there is more than 1inch of water, your tube will have overflowed into the larger outer cylinder, to measure this:

  1. Follow the steps one and two above.
  2. Ensure that you have only one inch (or less) of water in the measuring tube by pouring some of the overflow back into the larger outer cylinder.
  3. Record the amount of water in your measuring tube to the nearest hundredth of an inch (0.00) on your data sheet. (it is ok if it is less than one inch, we will add these up to total at the end)
  4. Pore the water from your measuring tube out into your spare bucket.
  5. Take the cap from the rain gauge (the top funnel shaped piece) and place it inverted on your measuring tube, it will act as a funnel for your remaining sample.
  6. Pour water from your large cylinder into the measuring tube (again insure it's one inch or less).
  7. Record the amount of water in the measuring tube to the nearest hundredth of an inch on your data sheet.
  8. Pour the water from your measuring tube into the bucket.
  9. Repeat steps 6-8 until there is no more water in the outer cylinder.
  10. Add up the amount of water you've recorded (check where your decimal places are and make sure you match them up!) **
  11. Record the total amount of water on your data sheet.
  12. Pour out the water from your bucket and set up your rain gauge again.

**If you're not sure you added or measured correctly, you can use easily measure the water from your bucket again by repeating steps 6-10 using the water from the bucket and the measuring tube.


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