Can Water Carve a Canyon? Build a Stream Table to Test Erosion

The Grand Canyon is about 446 km (277 mi) long, and it was carved by running water. It’s hard for children to picture, but a stream table lets them watch erosion happen in ten minutes.

Build a stream table

You need: a disposable foil roasting or lasagne pan (about 30 × 23 cm), damp play sand, a paper cup with one small hole near the bottom (your “rain”), a measuring cup, books or blocks to prop the pan, a ruler and a tray or tub to catch water.

Pack damp sand into the pan, smooth it, and prop one end up on books to make a slope.
Put a small tub at the low end to catch water.
Fill the cup with 250 mL of water and let it drip over the top of the sand, so a steady trickle runs down.
Watch where the water goes. Look for a channel, eroded sand and a fan of sand dropped at the bottom.

A fair test: gentle or steep?

Question: Does a steeper slope carve a deeper channel?

Run the test with the pan propped on one book. Measure the channel’s width and depth with a ruler and record the amount of sand carried to the bottom.
Smooth the sand again, prop the pan on three books and repeat with the same amount of water.
Compare.

Keep fair: same sand, same dampness, same water amount, same height from which water drops and same starting surface.

What usually happens

On a steeper slope, the water flows faster and carves a deeper, narrower channel. It carries more sand downhill. At the bottom, where the slope flattens and the water slows, it drops the sand it carried in a fan shape called a delta.

The science

Moving water carries sediment, and faster water carries more and bigger pieces. Three steps are involved: erosion (wearing away and picking up), transport (moving it) and deposition (dropping it when the water slows). Over thousands to millions of years, a river can cut through hard rock and shape a valley or canyon.

Models like this are smaller and faster than real rivers, so we should say what a model can and can’t show. A real canyon takes a very long time, and rock is much harder than damp sand.

Protecting the land

Try placing grass, pebbles or small twigs on the slope, then run the water again. Plants and rocks slow the water and hold soil. See What protects a hillside from washing away?

Safety

Keep the work on a tray, mop up water and sand (sand is slippery on floors), and wash hands afterwards.

The activity is Can water carve a canyon? from Rocks and Erosion: How Land Changes Shape, which also includes Are all rocks the same? and How do rocks become sand? Sign up for three lessons free.