IIW

STEM Activity: How do rivers form?

A river is a naturally flowing channel of water that forms from a spring or places where rainwater and snow collect. ‎Typically, rivers originate in mountains, and run across the land until they flow into other rivers, lakes, and oceans. Rivers ‎are important to civil engineers because of their extreme ability to sculpt the Earth’s topography while they carry large ‎quantities of water and sediment to the land and sea.

In these activities, students will explore how rivers form in different landscapes. During the activities, note the similarities ‎and differences of the formation of the river due to the different landscapes.‎

Key Terms

  • River mouth: The location where a river flows into a larger body of water (also known as another river, lake, or ocean).‎
  • River source: The beginning of a river (headwaters).‎
  • Downstream: Toward or nearer the mouth of a river.‎
  • Upstream: In or toward the source of a river.‎
  • Meander: A loop or bend in a river.‎
  • Tributary: A smaller stream or river that joins a larger stream or main river.‎
  • Deposition: The accumulation of natural materials by a gradual process.‎
  • Erosion: The gradual wearing away of land surface materials, especially sediments, rocks, and soils, by the act of water, ‎wind, or a glacier.‎

Materials

  • Garden hose
  • Large plastic storage bin (optional)‎
  • Rectangular aluminum tray (baking pan)‎
  • Sand (enough to fill the tray halfway)‎
  • Watering Can
  • Items to prop up the tray: 2-4” blocks, rocks, or sticks (just enough to create an incline)‎
  • Notebook (to write down notes)‎

Preparation
The activities work best outside and with some adult supervision. Refer to the photos on the right as you work through the instructions. ‎

  • Use scissors to puncture a 2”-3” long slit near the rim on the short end of the aluminum tray. The end will be ‎referred to as the “downstream.” The opposite end will be the “upstream.”

 

 

 

  • Pour sand evenly into the tray until it is halfway full. Wet the sand with the mist setting of the garden hose and stir ‎until it is evenly moistened. Doing this will help ensure the sand stays inside the tray while the tray is propped on ‎an incline.

 

  • Place a large plastic bin under the slit on the short end of the aluminum tray if you want to catch the water and ‎sediment. You can also let it drain into the grass, an area with soil, or rocks (as shown).

  • During each activity, record observations and sketch the final resulting river.

Activity 1: Flat, Inclined Terrain Model

  • Smooth out and flatten the sand and prop up the tray under the “upstream” side to create a slight incline.

 

 

 

 

  • Predict what will happen when the water begins flowing. (What will happen to the sand? Where will the water ‎flow? Etc.) Take a picture before you begin.

  • Fill up the watering can or turn hose on to a steady, slow stream.

 

 

 

 

  • Let the water flow for a few minutes and watch.

  • Record your observations in your notebook.

  • Turn the water off and create a sketch of the sand and water. Compare to the “before” picture.

Activity 2: Hills and Valleys Landscape Model

  • Shape the sand in the tray to create several hills and valleys. Use your hands to carve out different formations in ‎the sand.

 

 

 

 

  • Predict what will happen. Will the same river formation occur? (What will happen to the sand? Where will the ‎water flow? Etc.) Take a picture before you begin.

 

  • Fill up the watering can or turn hose on to a steady, slow stream.

 

 

 

 

  • Let the water flow for a few minutes and watch.

  • Record your observations in your notebook.

  • Turn the water off and create a sketch of the sand and water. Compare to the “before” picture.

Optional Additional Activities‎

  • Add a large rock next to a valley that you’ve carved out of the sand and repeat the process.

  • What happens to your rivers during a heavy rainfall and flood? You can simulate this by increasing the flow of ‎water from the watering can or hose and see what happens.

Post Activity

  • How were the river formations similar?

  • How were the river formations different?

  • How did the hills and valleys affect the river formation?

  • Was the amount of erosion equal in each river? Was more sand carried away in one activity than another?

  • Did the sand erode evenly? Observe if different size particles of sand were carried away more or less by the water.

 

 

Engineering in the Real World
Civil engineers must address erosion in many of the projects they work on. Sometimes they’re specifically working on a ‎bank stabilization project where they’re trying to stop the erosion from happening in order to protect buildings near the ‎water. Other times, they’re designing a man-made channel to drain stormwater from a city and they need to make sure the ‎channel is made of the right materials (often concrete or large rocks called “rip rap”) so that damaging erosion doesn’t ‎occur. Where have you seen effects of erosion in your life? Key places to look are near rivers, creeks, waterfalls, or even ‎your backyard!