Steve MacMinn writes:
"I'm reading a book about water resources in the U.S., and it begins by discussing beavers (nature's little hydrologists). I learned some things I didn't know before:
"A family of beavers can build a 35 foot dam in a week. Where the streams have clearly cut banks and a channel with a uniform current, beavers build a solid bank dam with the poles underneath and earth on top; water discharges through an opening in the dam's crest. If the stream is wide, they bow the dam into the flow of water, increasing the structure's stability. When the young trees nearby are all consumed and the edge of the forest is too far away for the beavers to drag their branches easily, they dig canals about 2 feet wide and 1 foot deep in which to float the branches back to home base, sometimes extending these canals for hundreds of feet to reach new trees. If a riverbank is steep they build slides down to the water. Dams more than 4,000 feet long have been found, built by generations of beavers, and nineteenth-century reports describe dams encrusted with lime and half petrified, attesting to hundreds of years of continuous repair."
Beavers also apparently (almost) make great pets - they love to be petted and will jump up on your lap. There's just one shortcoming. They're hardwired to build dams. They will gnaw the legs off your furniture and use them to block up any opening in your house that looks like it needs a dam - doorways, the space between table legs, etc...
The book is: Water, a Natural History by Alice Outwater"