Thus far, we have performed only a few experiments dealing with erosion. This one can be done in the classroom without risking the result of clogged pipes.

Cut a V-shaped notch in one end of an aluminum foil pan. Weigh some dry soil, and fill the pan with it. Set the foil pan at one end of a larger pan, and raise the uncut end by resting it on a block of wood.

Each day for a week sprinkle a half cup of water on the soil at the top of the pan. A sprinkling can with several small holes in the nozzle would be best for this. Pour it gently.

At the end of the week examine the soil that has washed into the larger pan. The smaller, lighter materials fan out the farthest from the opening. (What is this fan called?)
This happens because the flowing water slows down as it fans out, depositing the heavier materials first and the lighter ones last. The materials deposited from rivers, as they slow down, are called "sediments."

If possible, study pictures of delta regions (e.g., the mouths of the Mississippi River and the Nile River) to discover where such deposits take place and the shapes formed
by the sediments.

What human purposes can the deltas sometimes serve?

What happens to sediments that are blocked by dams?

To find out, or to check your hypotheses, you could build a small, temporary dam in a gully or gutter of running water. You can also block the water by curving a large sheet of plastic or cardboard and impeding the flow with it. As the water rises behind the dam, observe what happens to the materials it carries.

Make an analogy to actual dams that span rivers. Discuss the problems of sediment buildup at dams, and some possible solutions.