Unit 2: Fluvial Processes that Shape the Natural Landscape

Unit 2 Learning Goals:

By the end of this unit, students will be able to:

• Synthesize their knowledge and understanding of how fluvial processes shape Earth's surface by the erosion, transport and deposition of sediment.
• Make connections between Earth systems and the interactions between the hydrologic cycle, fluvial systems, and the rock cycle.
   

Unit 2 Learning Objectives:

In order to achieve the learning goals, students will work through the following objectives.

• Objective 2-1. Students will create a scale model of a fluvial system and describe the processes of erosion and deposition of sediments.
• Objective 2-2. Students will observe how stream velocity affects weathering, erosion, and size of sediment particles transported and deposited in a river system.
• Objective 2-3. Students will identify and describe physical characteristics associated with the collection, transport and deposition zones in a river system.
• Objective 2-4. Students will discuss the impact of human activity on the quality and sustainability of a river system.

Unit 2 is an activity designed for an introductory geoscience content course that is aimed primarily at pre-service teachers. It may be used as part of the Interactions between Water, Earth's Surface and Human Activity module, or as a stand-alone activity. The curriculum is designed to build a strong foundation of pedagogical content knowledge for teaching Earth science. This type of course is common at state and regional schools with large teacher preparation programs. Activities are designed to foster group collaboration as students work in small groups (ideally in groups of 3–4) with a faculty member acting as the facilitator.

Unit 2 is designed to take two hours in a lab setting. It is not recommended for implementation in a large lecture class. Students should have prior experience with the formation of igneous, metamorphic, and sedimentary rock, and knowledge of density and velocity.

The content in this unit aligns well with Science and Engineering Practices, Disciplinary Core Ideas and Crosscutting Concepts in the Next Generation Science Standards (NGSS):

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In this unit, students explore connections between the hydrologic cycle and rock cycle. They discover how the hydrologic cycle is one of the driving forces behind the rock cycle as they simulate the process of erosion, transport and deposition of sediments in a fluvial environment. Students are challenged at the end of the activity to explain, based on observational evidence, the primary function of each subsystem (zone) in a river system and where each zone occurs within the river system.

Handout that guides students through the unit

Students take notes and follow the directions presented in the Unit 2 student worksheet (Microsoft Word 2007 (.docx) 4.7MB Nov18 14).

Students work in groups of four to read and answer questions on the worksheets. Once students have been guided to a particular point of understanding, they are asked to write down their thoughts and share them with the rest of the class. One effective way to do this is with small, portable whiteboards. This facilitated discussion is where much of the learning takes place or is solidified.

The role of the teacher is to facilitate, and to try to avoid directly providing answers. The worksheets are designed so that students can reach scientifically sound conclusions on their own. If they do not, the instructor/facilitator can guide the discussion to address any remaining misconceptions.

Initial ideas

To begin this unit, elicit students' initial ideas about Earth's water reservoirs with the following questions:

• The student handout (Microsoft Word 2007 (.docx) 4.7MB Nov18 14) includes two pictures (on page 1) taken during the same season along the Sacramento River. What factors do you think would cause the water to flow faster in one area of the river compared to another?
• You are planning a rafting trip requiring only basic rafting skills. Where along a river system do you think would be a good place to start — at the beginning, middle or near the end — and why?

This can be done in class or as homework prior to class. Students should have time to write down their own ideas first, then share them in small groups and with the class.

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Part 1: Characteristics of a River System

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A diagram showing the three zones of a fluvial system from the student handout.

Provenance: Julie Monet
Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.

This is a short introduction to river systems. Students can work through this part on their own in class or prior to class if time is short; images and photos from the handout can be projected and discussed as a group as well. The handout introduces students to three zones/subsystems of a river system, shown in the diagram to the right, and some basic vocabulary; they then use this information to describe a local river and identify which zone/subsystem is shown in several images of river systems.

Materials needed:

• Student handouts
• Topographic or shaded relief maps showing entire river systems with towns and roads

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Characteristics of a River System

Background Fluvial systems are the main factors in shaping the surface of the continents as they drain the water on the continents and move weathered material (gravel, sand, silt, mud) to the ocean basins. The appearance of rivers and streams is strongly influenced by the climate, geology, and the topography of the region. Although the appearance of rivers may differ from one to the next, all rivers have three subsystems (or zones) that define the entire river system: 1) collecting system, 2) transporting system, and 3) dispersing system.

The diagram to the right is a sketch of a prototypical river system with a dashed line between zones. Although there is typically only a gradual gradation between the subsystems, when you view them at a regional scale, you can recognize patterns characteristic of each subsystem.

Directions To answer questions 1-1 through 1-3 you will need to find a river on a topographic map of the state or county where you live.

Collecting system (Zone 1)

The collecting system is where the headwaters are located in the region where the river begins. The collecting system is typically a mountainous region containing a network of small tributaries that are created as water and sediment are funneled toward the main stream.

Question. What is the name of the town, county, or area where the river begins?

Transporting system (Zone 2)

This part of the river system consists of the main channel (trunk) and the major tributaries. The transporting system is where water and sediment that have been collected in the headwaters are transported downstream to a lake or ocean. This section of the river system will often contain meanders. These are formed by the combination of erosion and deposition of sediment. As the slope (gradient) of the stream channel decreases, so does the velocity.

Question. What are the names of towns or cities located along the transporting system?

Dispersing system (Zone 3)

This part of the river system is at the end of the river where the elevation of the river is nearing sea level. Here you can observe a network of distributaries that redistribute the water and sediments into the ocean. The fine-grained sediments (clay, mud) remain suspended in the water and continue to be transported and finally deposited into the bay or ocean. The coarser material is deposited at the shoreline and forms a delta.

Question. What body of water does the river empty into at the end of the dispersing system?

Observations Each of the following images illustrates one of the three subsystems in a river system. Identify under each image the type of subsystem and the zone in which it is located. If you need more information, refer to the general description of each subsystem in the previous section.

Part 2: Erosion, Transport and Deposition by Fluvial Processes

Students use a stream table to simulate the process of erosion, transport, and deposition of sediment in a fluvial environment. They are prompted to interpret the patterns they see (shape of the water pathways, amount of erosion, and deposition of sediment based on grain size) and connect them to the three zones/subsystems that they learned about in Part 1.

There are several terms that students should be prompted to use in describing their observations of river systems:

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Terms

Sediment: Material that has been eroded from preexisting rock.

Weathering: Breakdown of material caused by physical, chemical and or biological processes, often happening simultaneously. Weathering is a process that occurs in place.

Erosion: The process that moves weathered material by a transport agent (air, water, ice, gravity).

Canyon: A narrow, deep, often V-shaped valley, usually cut by a stream.

Meander: A half loop bend in the major trunk of the stream channel.

Floodplain: The region along the edge of the stream that overflows during floods.

Tributary: The smaller of two streams that meet to make a larger stream.

Distributary: A channel that branches off and flows away from the main stream channel (trunk of a river).

Delta: A deposit of sediment, approximately triangular in shape, formed where a stream enters a lake or ocean.

Prompt students to answer the question "Why study a river system?" in their handouts. Ask students to consider this question individually, then discuss in small groups before sharing with the class as a whole. After the group discussion, break into small groups to get students working on their stream tables.

Building a scale model of a river system

Ideally, each group of 3–4 students has its own set of materials to work with. Note: this is the same set of materials used in Unit 1 of this module with a few additions.

Materials needed per group:

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• Stream table tray: The tray used in this activity comes with pre-drilled holes and can be ordered from from Delta Education, (1-800-442-5444) for about $8.00 each (order number 1412098-WW). You can also use a plastic tray or an aluminum foil roasting pan that you can modify by drilling a 3⁄8" drainage hole into the edge of the tray or pan between the bottom and the drainage wall.
   
• Scraper: A wooden angle is used to smooth and shape the sand in the stream table. You can order a pre-made angle that fits an 11" wide stream table pan from Delta Education, (1-800-442-5444) for about $2.70 each (part number 010-2530-WW).
• Water source container: The water source container can be a 500-ml plastic container; you will need to drill a 5/32" diameter hole in the bottom of it to simulate flood conditions. Or the "water source, flood" container can be ordered from Delta Education: part number 230-2365-WW. The cost is $10.35 for a set of 8.
• Ruler
• Sponge
• 1" block of wood
• 1/2" block of wood
• Runoff catch basin or bucket
• Earplugs for plugging the drain hole
• Sand mixture (~2 quarts of sediment per tray) 
  The amount of mixture you need varies depending on the size of the tray, but the following mixture will fill 6 stream tables (22" × 11" × 2 1⁄2").
  • 5 liters or 2.5 lbs coarse sand (available from building supply stores and aquarium supply stores; try to find 3-grit sand, but 10- or 12-grit sand will also work)
  • 5 liters or 2.5 lbs fine sand (30-grit sand, also called "medium sand," is used in construction and works well)
  • 1 liter or 1 lb baking soda (from the grocery store) or clay (available from Delta Education for $4.00 per bag, part number 030-4920-WW)
    Place the components in a 10-gallon container. To combine them, add enough water to get it completely damp and mix well. When you are ready to set up the stream tables, put 2 quarts into each stream table tray.

A schematic diagram of the model setup is shown on the right. All of the instructions below are included in the student handout; each group of students can set up its own model if the materials are provided — you do not need to set these up ahead of time.

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Setting up the model:

• Add sediment and water to the tray. Add only enough water until the sediment feels damp, and mix well.
   
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  Use the wooden scraper to push the sediment to one side of the tray so it fills about ¾ of the stream tray (refer to diagram on the right), this should leave approximately ¼ of the tray bottom empty.
• Shape the sediment into a hillside, as shown in the image above, by gently patting the sand with your hands to form a wedge shape (A). The thickest side of the wedge should be farthest away from the location of where the river will eventually empty into a body of water. The "ocean floor" should be free of any sediment.
• After you form the hillside, add a slight indentation to the sediment forming a line down the middle of the hillside (B). This is meant to direct the flow of water down a central path.
• Be sure the catch bucket (F) is empty before running water through the system. Do not empty any water containing sediment down the lab sinks. Instead use a waste bucket that can be emptied later.

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Procedure

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• Once the hillside is formed (A), elevate one end of the tray using a ½-inch block (C), as in the image above.
• Place a ruler across the width of the stream table, about 4 or 5 centimeters (2 inches) from the edge of the tray (D).
• Cover the hole in the bottom of the flow container (E) with your finger and fill the container to the top with water.
• Carefully place the container on top of the ruler and center it over the indentation you previously made with your finger. Release your finger and watch closely as the water flows downstream.
• Look for any features that may develop on the surface of the hillside as gravity transports the rainwater downslope. Before the flow container is completely empty add another 500 ml to the container.

Students are prompted to answer a series of questions in the handout on pages 7–8, including drawing a sketch of their model fluvial system and labeling the zones/subsystems.

Part 3: How does slope affect erosion, transport and deposition of sediment?

In this final part, students conduct another experiment with the stream table model to explore how slope affects erosion and deposition.

Before students begin this next experiment, prompt them to make a prediction about what patterns they will see when they increase the slope of the stream (page 8 in their handout).

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Procedure

• Re-mix the sediment. Try to recreate the same wedge shaped hillside (shape and steepness) created in part 2.
• Increase the slope by removing the ½-inch block and replacing it with a 1-inch block.
• Pour 500 ml of water into the water flow container. Before the water has stopped flowing, add another 500 ml. Observe the formation of surface features that form in each zone of the subsystem.

Students are prompted to answer a series of questions in the handout on pages 9–10, including drawing a sketch of their model fluvial system and labeling the zones/subsystems and describing the effects of increasing the slope.

Summarizing Questions

After students have completed parts 1, 2,and 3, ask them to consider what they have learned by answering the questions on pages 10–11 of their handout. You can also prompt them to look back at their initial ideas as they respond to these questions to see what they have learned through this process. The two questions are:

1. Explain how streams and rivers are an important factor in the formation of sedimentary rocks.
2. Explain how stream velocity (assume the steeper the slope, the faster the velocity) relates to the transportation and deposition of sediment. Use specific examples from Part 2 and Part 3 to support your answer.
    

Students should answer these questions individually first, then share their answers with their small group. In their small group, they should then develop a labeled sketch to support their answer to question 2, and prepare to share the answer with the entire class. 

There are two options for setting up the stream table: you can confine the flow by plugging the drainage hole (image on the left below) or have continuous stream flow by leaving the hole open and letting water flow through into a catchment basin (image on the right below).

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You can choose between these two options based on practicality (easy access to sinks, for example) or to illustrate different concepts. You could ask half the groups to plug the drainage holes and the other half to leave theirs open and see what patterns of deposition emerge.

Comments on the sediment mixture:

If students oversaturate the sediment and/or are using sand that does not have a range of grain sizes, it can result in poor development of landform features. To avoid this:

• Use powdered clay instead of baking soda;
• Remind students to dampen and not to saturate the sediments at the start of the activity (this is especially important if you run lab sections back-to-back);
• Students must re-mix the sediment (not just reshape it) between Part 2 and Part 3.

Formative assessment occurs via the following:

• Facilitator listening in on group discussions of specific prompts to make sure that students are on the right track/holding productive conversations.
• Facilitator listening in on class discussions of specific prompts.
   
• Quality of individual student answers to specific prompts in the activity sheet.

Note: Assessable objectives are in normal font, and the writing/discussion prompts that assess those objectives are in italics:

Formative Assessment:
Objective 2-1. Create a scale model of a fluvial system and describe the processes of erosion and deposition of sediments.

Part 2, Question 2-3. In an actual river system, stream velocity naturally sorts the grain sizes over the course of the river system. The faster the flow of the river, the larger the grain size that will be transported downstream. Considering this information, where would you expect to find the largest rock and sediment size in a river system? Use the stream model to support your reasoning.

Objective 2-2. Observe how stream velocity affects weathering, erosion, and size of sediment particles transported and deposited in a river system.

Part 2, Question: 2-5. The diagram below illustrates the interaction between water as it flows downhill and rocks or sediment it pushes in the river channel or along the river bank. During this process kinetic energy in the water is transferred (causing a decrease in kinetic energy) to the solid material (rock or sediment). What type of energy increase causes the sediment to move downstream?

Objective 2-3. Identify physical characteristics associated with the collection, transport and deposition zones in a river system.

Part 2 Question 2-1. What do you notice about the shape, width and depth of the stream channel as you move away from the headwaters? (Zone 1)

Objective 2-4: Discuss the impact of human activity on the quality and sustainability of a river system.

Part 2 Initial ideas: Rivers are invaluable resources for plants and animals. Think about the significance of rivers and why it is important for scientists to study how a river system behaves. Brainstorm your ideas with your group and summarize your answers below. Be prepared to share your group's response with the class.

Unit 2 Summative Assessment:

Summarizing question Q1: 

Explain how streams and rivers are an important factor in the formation of sedimentary rocks.

Summarizing question Q2:

Explain how stream velocity (assume the steeper the slope, the faster the velocity) relates to the transportation and deposition of sediment. Use specific examples from Part 2 and Part 3 to support your answer.

References

Unit 2: Part 1 (Student worksheet pages 3–4)

Photos of river systems:

• Image 1: Sacramento River Delta, Sacramento, CA - From Wikimedia Commons
• Image 2: Roaring Fork River, Headwaters near Independence Pass, CO, USA - By TheBoyFromFindlay. Slightly color-corrected by Daniel Case prior to upload (CC-BY-2.0), via Wikimedia Commons
• Image 3: Cauto River, Meanders of the Rio Cauto at Guamo Embarcadero, Cuba.Meanders - Public Domain File - From Wikimedia Commons
• Image 4: Mississippi delta - By NASA [Public domain], via Wikimedia Commons
• Image 5: Arkansas River, Headwaters near Leadville, Colorado - From Wikimedia Commons
• Image 6: Delaware River, above Walpack Bend - Photo by George Ratliff From Wikimedia Commons

Resources

Activity 2: Part 2 & 3

• All materials can be ordered from Delta Education Phone 800-442-5444 - Fax 800-282-9560 
   
• Sand mixture recipe from: STREAM TABLE INQUIRY A Professional Development Curriculum from the Institute for Inquiry®