Stream Table

Engage

20 minutes

Ask students to think about the glacier photos that they analyzed. What were some of the changes to the landscape they observed after the glacier had receded? In addition to exposing land that was previously covered by ice, the water released can change the landscape and the quality of water in streams. Show them the stream table and explain that you can use it to show the effects of a stream on the land. See Teacher Background for Stream Table instructions.

Explore

50-60 minutes

Ask students to closely observe the stream table before you begin, noting how the surface appears.

Modeling Erosion: Build your stream table with sand. Use a watering can to simulate “rainfall” by holding it slightly above the high end of the stream table. Observe the small streams that form in the sand and drain into the original stream you etched out.

Ask students to watch the flow of water as it erodes the sand. What do they notice? How are the different grain sizes affected by the water flow? How is the water flow affected by different size sand or rock particles?

Ask them to sketch the resulting landscape and write an explanation of how a stream can erode the land.

Modeling Head-Cutting and Canyon Formation: Build the stream table with sand, but mound up the sand at the upper end of the tray. Create a channel through the top of the mound. Pour water from the upper end in a steady stream and observe.

Ask students to watch the flow of water as it erodes the sand. What do they notice? What happened to the channel at the edge of the mound?

Ask them to sketch the resulting canyon and write an explanation of how the water can extend the length and depth of the canyon.

Modeling Siltation: Build the stream table with potting soil, or potting soil over a base of sand or gravel. Place the tubing in the lower end of the stream channel and place the funnel below the end to direct the flow into a bucket. Use the watering can to simulate rainfall, continuing to pour until water runs off into the bucket. If you used a pan instead of a cookie sheet, you can mound up the potting soil on either side of the channel and pour water from the watering can down the sides as well as at the upper end until it runs off. Continue to add water until the water collected at the end is cloudy or muddy.

Ask students to watch the flow of water as it falls on the soil. What do they notice? What is the difference in the size of particles that get moved by the water and make it cloudy or muddy?

Ask them to write a description of what happened. Ask them to consider how muddy water might affect the plants or animals that live in the water.

To model the effect of increased flows that would occur with accelerated glacial melt, use the watering can for a set period of time and keep a sample of the runoff, then pour water down the sides of the mounds on either side of the channel or into the upper end of the channel for the same amount of time and take a sample of the runoff. Compare the two samples. Which is more cloudy or muddy? (This is a good lead-in to the Secchi disk activity.)

Have students look for examples of erosion, canyon formation, and siltation in their local watershed. They can look at a map of Alaska to see where the glaciers and ice fields are located in relation to the examples they found. Is it possible that the examples were a result of glacial retreat? If not, what caused the change?

Elaborate

30 minutes

Watch the visualization of a canyon-forming process

Modeling a Delta: Form a large pool of water (a lake or ocean) at the end of the stream table. Watch as sediments are carried and deposited at the edge of the ocean. After one delta has formed, raise the stream table to allow new deltas to form.

Modeling Melting Glacier Effects: Mix 1 liter of sand and gravel with 500 ml clay and water. Freeze the mixture until solid. Place the frozen mixture on the raised portion of the stream table, and observe the results.

Evaluate

This unit is followed by Transparency/Turbidity.