Sedimentator Simulates River Erosion and Motion
A Geography and Geology Activity on Stream Geomorphology
Rivers shape the places that they move through. At times, a river gradually erodes its bed, moving small quantities of dissolved and suspended sediments down to a lake or ocean. During flood peaks, a river moves larger rocks and may even bounce boulders along the river bottom. Large quantities of rock and sediment move quickly down the river channel.
Rivers also deposit sediment in the river channel. While they undercut banks and move materials from the riverbed in some places, they also deposit these materials in other places, called bars. After a large flood event that moves onto the floodplain, sediment, large rocks and woody debris like logs end up on the river bank.
River Geography Activity for the Classroom
Students who are studying rivers may not have the opportunity to watch a river go through its annual cycle. A visit to a river is an opportunity for students to examine undercut banks, bars, and look at the different sorts of rocks that are carried by a river. By making a simple tool called a sedimentator, a geography class can also create different river scenarios in the lab.
Materials Required for This Geography Lab
To make a sedimentator, purchase tough clear plastic tubes that are one to two feet long. The tube must have a removable end. It is possible to reuse old tubes that used to contain toys or tennis balls. A clear plastic mailing tube is a good choice for purchase.
Pre-Teaching River Geomorphology
Discuss the different sizes of rocks that rivers can move. These include tiny particles, sand and mud, gravel, hand-sized cobbles, and even boulders. Talk about the times when the different rocks might move. While rivers constantly carry small particles and slowly move gravel along the river bottom, it takes a flood to move very large rocks like boulders.
Discuss the ways that rivers move rocks. These processes include traction, saltation, suspension, and solution. Rocks can roll along, bounce along the river bottom, move as suspended solids, or be dissolved in the water.
Talk about how rivers shape their landscape. Where do the rocks come from and go to? Rocks move from cliffs, river banks, and the river bed. Some stay in the river and move to form bars. Others move slowly down the river until they reach a lake or ocean.
Building the Sediment Tube
Find sediment to put into the sedimentator. Place different sizes of rocks in the tube. Since the sedimentator is a microcosm of a river, the gravel can be used to represent boulders, while pebbles represent smaller rocks, such as cobbles.
When the rocks are in the tube, add water until the tube is nearly full. Shut the open end. Ask the students to examine the way that the rocks and water are arranged in the tube.
Watch Rocks and Water Move
Move the tube from side to side. Fast movements simulate a flood. Slow movements simulate the river during the slower summer months. Note what happens to the rocks as the tube moves. Do they jump along the bottom, roll, or move in the water column?
After students finish, prop the sedimentator on a flat surface and make a note of how the sediment settles. What settles first and last? Is there any sediment still in the water column?
Building and using a sedimentator brings river processes into the classroom. It’s a good way to follow up on or introduce a geography field trip, study erosion, or examine river movement.
River Movement and Erosion
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