River Expeirements

In my 9th grade class my group did an experiment with Diatomaceous earth. We raised the container and ran water down it to make a river with an erosion. Then we used sand, and also raised it up too, and made a dam in the sand and used foam to stop the water. We made it work with just little water going through the foam. In my hypothesis, i thought that the foam wouldn't work and that the water would soak through it. My hypothesis was incorrect, cause the water did not soak through it, it went under it.