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Streams and Water Quality

Hydrogeologists and environmental scientists often study streams and lakes to determine the quality of the water. Water quality depends on several factors including sediment load and pH (level of acidity). Water quality in these environments is important, because this is where many people get their drinking water. In this activity, students will measure stream velocity, sediment load, and pH.

Grade Level: 9-12

Make sure students aren’t too close to the water, so they won’t fall in. Take special care after a rainfall, when the banks can be muddy and slippery, and the water may be moving more quickly than normal. Be aware of weather and flash flood warnings. Make sure that your stick or other floating object is handled with care so as not to cause injury from a sharp point or edge. Bring a first aid kit.


  • Stopwatch
  • Measuring tape/meter stick
  • A stick or other floating object that can be discarded after experiment
  • pH paper and corresponding color chart
  • Paper and pencil
  • Calculator

For the Teacher
Prior to conducting this activity, particularly step 6, the teacher should determine the cross-sectional area of the stream. Measure the stream’s width with a measuring tape, and find average depth with a meter stick. Cross-Sectional Area = Average Depth x Width.


  1. Travel to a local stream, preferably a place where it is easy to stand on the bank. With the measuring tape or meter stick, measure out 2 meters parallel to the stream.

  2. Have a student stand at one end of the measuring tape upstream (Point A) and another student stand at the other end downstream (Point B). Hand the student at Point B a stopwatch.

  3. Hand a third student a stick or floating object that is large enough to be easily seen.

  4. To measure the velocity of the stream, the student with the stick drops it in the stream about 2 feet beyond where the student at Point A is standing. When the front end of the stick reaches the measuring tape at Point A, then that student says “Go,” and the student at Point B starts timing. When the front end of the stick reaches the end of the measuring tape at Point B, the student at Point B stops timing. Record the time on the stopwatch.

  5. To calculate the velocity, the equation is Velocity = Distance/Time. So in this case, Velocity = 2 meters/X seconds, where X is the time on the stopwatch. (For example, if the time on your stopwatch is 2 seconds, then the Velocity = 2 meters/2 seconds, or 1 meter per second.)

  6. After finding the velocity of the stream, calculate discharge, the amount of water flowing past a certain point per second. An important indicator of what organisms live in the stream, discharge also influences a stream’s ability to dilute chemical pollutants. To determine discharge, use your measurement for the stream’s cross-sectional area, which is expressed in meters squared, as indicated above. So the equation for discharge (Q) is Q = Cross-sectional area (A) x Velocity (V). (For example, if A is 10m ² and V is 1m/s, then Q is 10m ³ /s or 10 cubic meters per second.)

  7. If there is time left, find the pH of the stream using pH paper and a color chart. Simply take a piece of pH paper, dip the end of it into the stream for a few seconds and pull it out to see if there is a color change. Then use the pH paper color chart key to determine how acidic or basic the water is.

  8. Discuss how the velocity, discharge, and pH of the stream might affect the biology of the stream and the quality of the water as a source of drinking water for humans. Why is the stream acidic? Why not? Could there be human or animal contamination? Does the stream’s velocity affect which animals you see in the stream? Are there fish or insects? How many and how big? Discuss the biodiversity of the stream. Are there many different types of organisms or a lot of the same kind of organism?

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