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Watershed – A Stream Table Model (FBCEC)
Geology - Erosion
Participants will use a stream table model to learn about a flowing body of water and its watershed. The table will show how factors affect the banks of a stream, the watershed and the body of water into which the water flows.
|Grade Level||8 - 12|
|Recommended Setting||Indoor or outdoor classroom|
|Location||Fred Berry Conservation Education Center, Yellville, AR|
Education Program Coordinator, 870-449-3484
|Duration||1 - 1.5 hours|
|Suggested Number of Participants||Up to 18|
- Describe how flowing water can alter the landscape.
- Demonstrate erosion, transport and deposition of sediment.
- Identify factors that contribute to and slow down erosion.
- Compare the features of young and old streams.
- Simulate how watershed introduces pollution.
- Relate lesson concepts to Crooked Creek.
2 (or more) large buckets
Drain and siphon hoses
Pebbles and stones
Pudding or Kool-Aid powder
Stream table kit
A stream’s water flow forms features such as cut banks, point bars, plunge pools, meanders and deltas. Several factors can influence where and how these form. A watershed is the land area drained by tributaries leading toward a major stream or river. Floods, erosion, drought, natural or human activities can affect the watershed and the streams to which it drains.
- Set up a pair of stream tables prior to the participants’ arrival. Show one of the tables and briefly discuss the different things that might be demonstrated.
- Show the parts of the table and how to use it. Tell them they will use the table to better understand bodies of running water and the watershed that surrounds them.
- Part one: rapids, waterfalls and plunge pools
- Ask participants to describe a favorite stream or river and if they considered what contributed to its characteristics. In the first demonstration, they will learn why streams change and why the source looks different from the mouth.
- Close the drain tube with a clamp. Pour water into the outlet side until it contacts the sand. Slowly pour water into the inlet side of the rapid stream trough (RST). Tell the participants this represents the headwater of the flowing body of water at the top of its watershed. As the water flows over the sand, pebbles and stones, the sand and smaller pebbles will wash toward the ends of the RST, which shows a waterfall. The material will be washed over the edge and onto the running body of water, forming a plunge pool in the sand. Have them stop pouring water when most of the sand has been eroded.
- The larger stones will be left behind. This represents rapids, part of the stream’s youth stage. In the youth stage, the flowing body of water has a steeper slope and more velocity or force.
- The waterfall, which occurs at the outlet side of the RST, shows that the running water also erodes the material supporting it. Waterfalls slowly erode the base materials they flow over, causing a gradual retreat of the waterfall until it no longer exists. At this point, ask the participants to describe what is occurring at the base of the waterfall.
- Discuss the plunge pool that formed at the base of the waterfall. Explain that the force of the falling water and the materials that have fallen erode a hole by hydraulic action. The eroded material will be transported downstream as sediment.
- Part two: meanders and deltas
- Have a participant slowly pour more water into the RST. There should be enough water falling into the table to begin flow. The water should flow through the meander and into the standing water at the outlet side of the stream table. Observe the water flowing through the meander curves. Explain that the stream or river tends to meander during its mature, older age. Ask them why. Explain that the slope declines and the velocity decreases. The obstacles in the path of the water cause the water to change direction and meanders form.
- Discuss what is happening to the outside edges of the banks as the water flows through the meander. They will notice that cut banks are forming due to increased velocity at the curve. They will also notice that the inside of the curve has a slower velocity, and sediment will deposit in those areas. This forms point bars.
- The water continues to erode its banks and carry the material as sediment, which is deposited as the flowing body of water loses velocity.
- Ask the participants to observe where the water flowing through the channel enters the standing water. Explain that when the water flows into a standing body of water, velocity is lost and sediment deposits form a fan-shaped delta.
- Part three: changing variables
- Change the slope of the table and repeat the activity. What is different about the stream flow?
- Place excess dirt along the bank and spray water to represent rain. Ask what happens to the bank when there is no vegetation on it. Next, place drops of food coloring or chocolate pudding powder on the surrounding soil. This represents pesticides, manure or other pollutants surrounding the stream. Spray more “rain” on the area and watch what occurs.
- Place vegetation into the soil and repeat the process. Discuss how vegetation stabilizes the banks and how it absorbs some of the pollutants that enter the water. Ask if the vegetation could filter all the pollutants. How can the adjacent land be adapted to lessen these destructive factors?
- After using the stream table, show the large map of Crooked Creek. Have them describe the phases of the creek and the surrounding water shed. Point out developed areas of the creek and how they may affect the creek and the organisms living in and around it. (Note: Make sure the stream table is dry prior to this activity.)
Hike the creek bottom trail at FBCEC and evaluate the stream features. Have participants point out, map or record cut banks, point bars, meanders, falls or rapids, pools, etc. Are there areas susceptible to erosion or contamination by runoff?
- Describe the following stream features and how they form:
- Cut bank
- Plunge bar
- Point bar
- Explain how sediment forms and list some materials it might consist of.
- Distinguish between erosion, transport and deposition.
- Describe how a buffer zone of trees and other vegetation can protect a stream.
- Write a proposal to stabilize the eroded bank above and below Kelly’s slab on Crooked Creek.
- Dobson, Clive and Gregor Gilpin Beck (1999). Watersheds – A Practical Handbook for Healthy Water, Firefly Books, Ltd., Buffalo, NY.
- Murdoch, Tom and Martha Cheo with Kate O’Laughlin (2001). Streamkeeper’s Field Guide – Watershed Inventory and Stream Monitoring Methods, Adopt-A-Stream Foundation.
- Pex, Deborah Rodney (1994). What Is A Watershed? America’s Clean Water Foundation, Washington, D.C., and Association of State and Interstate Water Pollution Control Administrators.
- Watershed Protection – an activity book, Project WET International Foundation, 2003. www.projectwet.org; firstname.lastname@example.org.
Cut bank – feature of streams shaped like a small vertical cliff, formed by soil erosion during high rainfall and higher-than-average water levels as the stream collides with the river bank; found in abundance along mature or meandering streams and also known as a river cliff
Delta – a low triangular area of alluvial deposits where a river divides before entering a larger body of water, such as the Mississippi River delta
Deposition – when material is added to a land mass such as sediment in rivers and streams
Erosion – the natural process by which the surface of the earth is worn away by the action of water, glaciers, winds, waves, etc.
Meander – a turn or winding of a stream
Plunge pool – water remaining in the deep, circular cavity (plunge basin) at the base of a waterfall after the waterfall has ceased to exist or the stream has been diverted; also known as waterfall lake
Point bar – low, curved ridge of sand and gravel along the inner bank of a meandering stream, formed by the stream’s slow sediment deposit when its velocity drops along the inner bank
Sediment – mineral or organic matter deposited by water, air or ice
Transport – to move matter from one place to another
Watershed – area bounded by a hydrologic system draining into a body of water within which all living things are linked by this common water source