How strong is a beaver dam?

These pictures don't really do this dam justice, but if you
look closely, you can see that the pond behind the dam is
suspended about 3 feet higher than the spillway by this
marvelous specimen of beaver engineering.

This was following the large tornado that brought
heavy rain.  The water is running swiftly over
the beaver dam.

About 25 feet beyond the dam, the water
spills over this naturally created waterfall.

You can see the waterfall in the background. 
The stream of water continues, flows into
a man made tin whistle, under the road, and into
Wolf Creek.  Wolf Creeks winds southward for
several miles before emptying into the
Cimarron River.  The Cimarron R. eventually
joins the Arkansas R. which is a major
tributary of the Mississippi R.