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Hands On Erosion

By Liz Clift

Editor’s Note: This post provides a hands-on experiment you can do with children to help them understand how erosion and floodplains work to re-distribute nutrients, especially in flood events. You may want to couple this with reading news reports about floods (new or old) for older children, or with a visit to a local brook, creek, stream, or river to try and identify high (or low) water indicators, such as damage to trees, bank erosion, detritus or debris from previous floods, or to observe how or if the bank has been stabilized through placement of riprap or vegetation.

Years ago, I lived near a pond. During heavy rains, it overtopped its banks, crept toward the nearby playground, and over a walking trail. It would back up into its inlet, which was lined with riprap and willows. During these rains, it seemed impossible that when the waters receded the fish and other animals that lived in the pond would retreat as the water dropped.

But of course, for the most part, the fish, turtles, crustaceans, and other animals retreated as the water levels returned to normal. The flood waters would leave detritus—dead grass, small animals tangled up in the summer clots of algae that snagged on the blue grass that surrounded most of the pond, decomposing leaves—and nutrient-rich muck. No one ever did anything about the detritus. Sometimes geese or ducks would pick at it, but for the most part, it decomposed along the upper banks of the pond.

This is similar to what happens when other bodies of waters, such as rivers, flood—and part of what has made flood plains historically beneficial places for agriculture. The flood waters deposit nutrient-dense material onto the flood plains, and over time, these materials build up.

Modified fluvial plain, from a Prentice Hall image by an unknown artist

You can replicate this for children in your life several different ways. One way is with andwich cookies and a milk (not chocolate) of your choice. You’ll need at least one sandwich cookie for each person who is participating in the experiment, a small cup of milk for each participant, and a shallow-bottomed bowl or a plate with fairly high edges for each participant.

Start out by placing the sandwich cookie(s) at the bottom of bowl on one side. Replicate erosion by slowly dribbling milk over the sandwich cookie and observing what happens. You might ask the children if they notice the milk turning colors. You might ask if they notice small crumbs from the sandwich cookie being carried away.

Ask the children to observe what happens as the sandwich cookies continue to soften. Does the erosion speed up or slow down? What happens if you add more milk?

They should see the sandwich cookie “eroding.” They should notice that the crumbs follow a particular pattern (the exact results will depend on the bowl or plate you’re using).

Ask the children to pour more milk in to represent a flood. How does this change the distribution of the crumbs? What happens to the sandwich cookie?

You can ask children to use a straw to gently suck up some of the milk (some crumbs will come too, and that’s okay). This will allow them to better see how the crumbs are distributed.

You can repeat the experiment using sandwich cookies that are pre-crumbled and see how that changes things.

You can also do this with other cookies, based on dietary needs or preferences. You might do it with some potting soil and water on a cookie sheet or in the garden. The goal is to help children engage in ecological processes, so that they can better understand not only what they see in the natural world—but so that they might grow to care about it.

You can also incorporate landscape architecture or engineering (does arranging the sandwich cookies or soil in a different way change what happens when you add milk/water? How can you slow erosion through design? Can you alter patterns of deposition?

Give it a try. Get dirty.

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