Mapping the Streambed

Have you ever wondered what the bottom of a river or stream looks like? How about the ocean? Some say that there are hidden cities at the bottom of the sea, but how could you tell without scuba diving to the bottom?

Scientists have long asked the same questions about the bottom of large waterways like rivers and streams. Scientists can tell a great deal of information about the flow of water, ecology and history of a stream from the structure of it's bottom. This activity models the process scientists use to map stream and river bottoms.

Materials

Procedure

  1. Construct a data table similar to the one below in your lab report.

Distance downstream (cm)

Depth (cm)

0

5

10

15

20

25

  1. Attach a washer to a 15 cm piece of string. The washer will act as a weight to take the end of the string to the bottom of the stream.
  2. Use a non-permanent marker/pencil to mark the long side of a model stream container every five centimeters. Label the points from left to right starting at zero. These marks represent points where we will measure the depth of the stream.
  3. Starting at the 'zero' cm point on your scale, using the middle of the stream, lower the washer end of the string into the stream until in just touches the bottom.
  4. Record the depth of the stream by pinching the string at the highest point the water rises on the string. Remove the string, making sure to keep pinching the string, and use a metric ruler to measure the length of string from where your fingers are pinching to the bottom of the washer. Record the depth in your data table.
  5. Continue recording the stream bed depth for the remaining pencil marks.

Analysis

  1. Make a two dimensional picture of the stream bottom by constructing a graph plotting depth vs. distance.

Questions

  1. A scientist would say that your graph does not accurately depict the bottom of the stream. How could you manipulate your graph to better depict a profile of the stream bottom?
  2.  
  3. How could you manipulate the data so that a graph constructed from the data would more accurately depict the stream bottom?
  4.  
  5. On your graph, suggest land forms that may account for the peaks and valleys on the bottom of the stream.