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CALCULATE THE SPEED OF MOVING SURFACE WATER

We're going to learn to calculate the speed at which surface water flows. There are several different ways to make this determination:

a. Float an object, such as a cork or small, thin piece of wood, onto some moving water (e.g., a stream or gutter flow), and measure the distance the object travels in 1
minute or some specified number of seconds. For example, an object placed in moving water might travel 88 feet in 1 minute.

We can convert the rate from feet per minute to miles per hour, using simple mathematics: Eighty-eight feet X 60 minutes (the number of minutes in an hour) = 5280 feet
per hour or 1 mile per hour.

b. Mark a 100 foot distance along a straight-flowing portion of a stream. Float an object between the marks, and record the time. If the object travels 100 feet in 25 seconds, then dividing by 25 gives 4 feet traveled in 1 second. The speed per hour can also be calculated: 3600 seconds (the number of seconds in one hour) X 4 feet
per hour = 14,400 feet, or approximately 2.7 miles per hour.

This activity does not address the fact that surface water often travels at a different rate of speed, and often in slightly different directions than deeper water. Also, it is
interesting to note that water within the same waterway will often flow at rates of speed that differ as from one side of the waterway to the other side. In a stream or river that meanders (twists and turns in wide or narrow turns, rather like a mountain road), the water on the outside of the curve will travel faster than the water on the inside of the curve.

Why do you think it is that we need to know the speed of moving water, anyway?

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