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Measurement In Rough Seas

Keep a level head with this stilling well

Australian Curriculum links

  • Science > Earth and Space Sciences > Year 4 > ACSSU075
  • Science > Nature and Development of Science > Year 7 > ACSHE223
  • Mathematics > Measurement and Geometry > Year 4 > ACMMG084

You’ll need

  • Large, deep container
  • Ruler
  • Large spoon or spatula
  • Clear plastic cup
  • Scissors
  • Permanent marker pen
  • Blu Tack
  • Water

Try this

  1. Half fill the large container with water and measure the water level with a ruler.
  2. Now simulate a rough sea by sloshing back and forth with a spoon or spatula. How easy is it to read the water level now?
  3. Empty the water into another container so you can start again. This time you will use a stilling well to measure the water level.
  4. Using the marker pen, place a mark every 1 cm down the cup (like a measuring cup).
  5. Use the scissors to poke holes every 2 cm in a vertical straight line down the cup.
  6. Use Blu Tack to secure the plastic cup to the base of the large container.
  7. Pour the water back into the container and watch as the cup slowly fills until the water in the cup and the container are at the same level.
  8. Use the spatula to slosh the water in the container. Can you read the level of the water in the cup?

What’s happening?

It’s very difficult to measure the water level when the water is sloshed around in the container. The cup acts as a wave break while still allowing water to flow in and out of the small holes. This is the same way a stilling well is used in the sea to protect tide gauges from the rough seas, making it easier to measure the sea level at a given point in time. Many measurements are taken during the day because the tide rises and falls.

In the past, a scientist would go out to the tide gauge and take measurements at particular times every day. Recent tide gauges use electronic measuring devices that are inside a floating buoy. They also require a stilling well to keep them steady while the readings are recorded and transmitted back to land or up to satellites.