My oldest son (8-years old when I wrote this Instructable) is in Cub Scouts.
As part of one of the requirements we were trying to fulfill, our Wolf/Bear Den (combined meeting) performed Elective 15, Water and Soil Conservation, to earn an arrow. (This is all part of the Cub Scout Bear handbook, shown in one of the photos in this step.)

This Instructable shows how our Wolf (and Bear) Den met Requirement 15 (b) Conduct a soil experiment, and (d) found out what erosion is and what kinds of grasses, trees, and ground cover the cub scouts should plant to help limit erosion in one of our meetings.

My kids and I made a video using our sample material covered areas to perform the erosion experiment. It's 2-minutes long and shows what came out of the different erosion scenarios as water was poured over them.
As always, my videos are just for giggles and fun, so please watch it as if you were eight to nine (8 - 9) years old!

Step 1: What Is Erosion & What Does It Look Like?

So the question that had to be answered by the Cub Scouts (part of Requirement 15d) is "What is erosion?"

The simple answer is that erosion is the process of eroding or being eroded by wind, water, or other natural agents.*

What does "erode" mean?

Again, the simple answer is to gradually wear away soil, rock or land by natural elements such as wind, water, or other natural agents.*

I am a Civil Engineer by trade. Because I am a mother however, I tend to answer things very simply, and show my children (if possible) what the answer is.

What does erosion look like?
While driving around for my job one day, I caught a glimpse of a two very real examples of erosion, and those photos are attached to this step.
One set of three photos is of a hill that has distinct lines that are caused by eroding material. I zoomed in as close as I could get to show the erosion marks - probably caused by water drainage.
The second set of two photos is a good example of three different types of ground cover, rock, compacted soil, and bark. (The forth could be considered the asphalt, if you want to be picky.) The photos show a hole where water drained off the road, down the path of least resistance, and eroded the material by the edge of the embankment.

Please feel free to use these photos in your own Erosion Experiment, by giving me credit for the photo itself. You can download the photos from Flickr: Erosion Photos by DeAndrasCrafts on Flickr

*Indicates answers to questions asked into the Google search engine box.

Step 2: Performing an Erosion Experiment

I'll admit, the entire basis of our Cub Scout erosion experiment was based off of the Pinterest pin you see in the photo above.

I did not think I was going to do an Instructable for this Experiment, just a blog post, so my research was limited to asking the Den Leader what type of experiment we had to perform.

She was very happy with this proposal and on we went with it.

Anyway, there is no link to the attached photo I pinned to my Scouts board, so I did what any crafty-Engineer mom would do and did my own version of the photo using items that we had nearby or for our home.

Steps 3 through 5 show how we prepared for the experiment, and Step 6 describes what we could have done differently if this experiment was for a Science Fair.

Step 3: Prep of Containers

What we used for the containers:

three (3), clear, one-gallon size, square-based plastic water containers to hold our soil/cover material
three cut-off tops to 2-liter size clear soda pop bottles
twine
hole punch
measuring cup (we measured the rock)
bottle to hold and pour the water for the erosion scenarios

Preparing the erosion scenario containers:
As I used a box cutter to prepare the containers, I cut about one (1) inch or so of plastic off the top of it, after removing the label. I cut the container using my steady hand (insert snorting laugh) and recycled the plastic piece that came off.

In a previous Cub Scout meeting, we planted sunflower seeds inside the bottom half of recycled 2-liter soda pop containers. There's a photo that shows the sunflower sprouting in the soda pop container and the top of the container cut off in front of it.
The same cutting operation as described above with the box cutter was performed to get the top off the three clear soda pop containers, and those were done about 3-inches or so below the inlet of the soda pop container.

Prepare the water catch:
With the hole punch, I pushed the entire hole punch tool to the end (I would estimate about 3/4-inch from the tip of the punch itself) so that the hole wouldn't tear if it were closer to the edge of the cut plastic.

I measured the string so that it would hang just below the lowest point of my kitchen table, as we knew this experiment was going to be performed inside.

I tied a double knot on each end of the twine and hung the water catches around the ends of the FULL erosion scenario containers.

Step 4: Erosion Scenarios

What we used to demonstrate various erosion scenarios:
1st Scenario - grown grass from seeds (I talk about this more below)
2nd Scenario - rock (we used a size 3 sieve, or more specifically 'pea gravel') over loose soil
3rd Scenario - loose soil over rock

We filled all three containers to about 1/2 of the opening was uncovered.

Scenario 1: Soil covered by grass
I knew I wanted to use grass for one of the three containers to show erosion.
We didn't have grass seed in our home, so we used what my husband calls a grass seed/lint mixture (Scotts Patch Master Sun and Shade Mix ) to use for that container.

I prepared and planted the grass seed/lint mixture in one of the three containers, a month prior to the meeting we were going to have.
Note: This process could be replaced by using rolled sod, something I wasn't will to pay for for the purposes of this experiment. I go into more detail of what other options could be used to demonstrate erosion in Step 6.

Scenario 2: Soil covered by rock
All of the rock was washed in a strainer to get rid of any loose dust that might have been a nuisance to some of the boys who have allergies.
I measured the rock into 4-cups to fill the top half of the 2nd erosion scenario (rock over soil) and 4-cups of rock to fill the bottom half of the 3rd erosion scenario (soil over rock.)
For this second scenario, the bottom half of the container was filled with dirt, while the top half was filled with 4-cups of the size 3 sieve rock.

Scenario 3: Rock covered by soil
We had planting soil from our local hardware store (so that we could plant the sunflowers.)
My cub-scout son helped me prepare these scenarios so he placed the soil over the pre-measured 4-cups of rock.

Step 5: Performing the Experiment W/the Cub Scouts

At the beginning of the cub scout meeting, we talked with the boys what erosion was, what erode meant and what kinds of ground cover there was around our neighborhood.

I asked the boys which of the three types of scenarios would allow the most material (soil or rock, not water) to come off into the catch. Two of the three boys stated that the soil over rock would come off the most (Erosion Scenario No. 3) and one stated that the rock would pour out of the hole the most after the water poured over it (Erosion Scenario No. 2.)

To perform this experiment with the boys, I removed the caps from all three of the erosion scenarios and we dumped out any initial material that fell from the opening.

One boy poured the water into the soil covering rock scenario (No. 3) and the soil fell easily into the catch along with the water.

The next boy poured the water into the rock basin covering the soil (No. 2.) The rock stayed put, and the water came out much cleaner than the soil covering the rock.

Finally, the third boy poured the water over the sparsely grown grass (Scenario No. 1.) The water was completely emptied out of the container and no water came out at all from the initial pouring.

"What's happened?" One curious Cub Scout asked.

"The grass has grown roots into the dirt we can't see. Those roots are keeping the water in the soil." I told him.

We filled the container again and continued to pour more water over the sparsely grown grass. The top layer of grass "broke" and soil and water finally poured into the catch.

Conclusions

The boys made the conclusion that the uncovered soil washed away more than the rock and the grass. In our experiment, Scenario No. 2 or the rock covered soil had the cleanest water in the catch, although the boys made the observation that the grass covered soil could hold more water although it still allowed some soil to pour out when the grass layer became over-saturated. Thus the rock covered soil eroded the least amount of soil.

We continued to talk about what kinds of other things we could have used to put over the uncovered soil so that the water would come out clean. The boys thought of many different ideas and I go over a few of them in the next step.

Step 6: Different Scenarios for Erosion

Because this experiment was performed for a Cub Scout Requirement and not a Science Fair, I wanted to give additional suggestions, and the other ideas the boys thought up while we discussed what type of Erosion Control was present in our neighborhood.

We started the meeting by going around our neighborhood and picking up garbage. This met several Cub Scout requirements and it got the boys a chance to look at the exposed areas of soil and what was growing as ground cover and landscaping.

I have attached three photos that show the three types of materials listed in this Erosion Experiment of sparsely grown grass, rock covered soil, and native soil (or dirt). Those photos were all taken in rural parts of the County I work in, and NOT around the city we live in.

The boys (think 8-9 years old) when asked "What type of erosion cover do we have in our neighborhood?" (or a question as part of Requirement 15d) gave answers for things that would also make good choices to test out for an erosion experiment.

Potential Options for Erosion Scenarios

sod or pre-grown roll out grass
an all grass-seed mix (not like ours with lint)
various bush-like ground cover, although I'm not sure if this would be possible to plant on a small scale
wild flowers or pre-grown flowers such as those planted for landscaping
landscaping bark
larger rocks than pea gravel
different layers of the above mentioned material in different scenarios

I hope this Instructable helps someone. Please let me know if it did and thanks for reading!