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Make a Rain Gauge
 
Although it’s August we can still expect a bit more wintery weather and rain.
After a good rain, you’ll notice a sudden growth spurt of your veggies because they love the rainwater (this is great!).  You’ll also see how all the snails and slugs come out  after rain (this is not so great!).
 
The Bureau of Meteorology reports daily on how much rain has fallen over the past 24 hours but you can make your own rain guage to read the rainfall in your very own back yard.
 
The most common instrument for measuring rainfall is the 203 mm rain gauge. This is a circular funnel with a diameter of 203 mm which collects the rain into a graduated and calibrated cylinder. The top of the rain gauge is ideally 0.3 m above the ground with no nearby objects to alter the wind flow.
 
Our rain gauge will be a bit more simple, and not quite so big!


Materials:
  • Empty 2 litre plastic bottle
  • Scissors
  • A few handfuls of clean pebbles, gravel, or marbles
  • Masking tape
  • Water
  • Ruler
  • Permanent marker
  • Rainy weather
  • Paper and pencil

Method:

  1. Carefully use the scissors to cut the top of the bottle off at the wide part just below where it begins to get narrow.
  2. Put the pebbles in the bottom of the bottle—these will help keep it from getting blown over if it’s windy.
  3. Turn the top of the bottle upside down—make sure there’s no cap on it! It’s going to act like a funnel—and place it in the bottom part of the bottle, pointing downward. Line up the cut edges and tape them together so the top part is held firmly in place.
  4. Use a long piece of tape to make a straight vertical line from the top edge of the bottle to the bottom. Use the marker to draw a line on the vertical piece of tape just a little above the top of the pebbles. This will be the bottom of your rain gauge.
  5. Set the ruler against the vertical tape so that the “0” line lines up with the bottom mark. Use the marker to mark every centimetre and half-centimetre (you could even mark millimetres if you want to be more precise)
  6. Set the bottle on a level surface and pour some water in until it reaches the bottom mark. Your rain gauge is now ready to go!
  7. Put the rain gauge outdoors—you’ll need to pick a really good spot! You want somewhere level that’s open to the sky and that’s not likely to get too windy, where the gauge isn’t likely to be disturbed. There shouldn’t be anything hanging over the gauge that could either block any rain or make extra raindrops drip into the bottle (like a tree or a power line or the edge of a roof).
  8. Pay attention to the forecast. On a day that you’re likely to get rain, make sure the water in the bottom hasn’t evaporated below your bottom mark; if it has, refill it to that mark.
  9. 24 hours later, if it has rained, check your gauge and see how high the water is now. Read the gauge by looking at the waterline straight on, at eye level. The water line's surface will be curved; this is the meniscus, formed as the water comes in contact with the container and creates surface tension. Your reading needs to be from the bottom of the curve for an accurate reading.
  10. Note down on your piece of paper the date and the amount of rain.  Then read the newspaper or go online and find out the official amount of rainfall in your area for the day and make a note of it—see how closely your figure matches the official one!
    The Adelaide rainfall observations from the Bureau of Meteorology can be found here...
  11. Alternatively you can create a chart and map the daily rainfall in your area.  Make sure you take your reading at the same time every day.  The Bureau of Meteorology do their readings at 9am every morning.  To make a rainfall chart, mark the days of the week along the top and 1cm to  15cm along the side. After drawing a dot for each day to indicate the amount of rain you received, you can use a ruler to connect the dots and see the fluctuations in the rain measurement for that week.
References: 
What’s Up? 45 Hands-On Science Experiments That Explore Weather, by B. K. Hixson, pp. 82-83 (Loose in the Lab Science Series, 2003).
Bureau of Meteorology Observation of Rainfall: http://www.bom.gov.au/climate/cdo/about/rain-measure.shtml
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