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What Happens to a Lake When Its Dam is Removed

A little more on beaver and river restoration.
Pre-beaver-wipe-out fur trapping, the little buggers were all over, and a lot of the rivers that we know as free flowing had beaver dams, marshes and meadows, so they weren't so "free-flowing". So, removal of a dam to create a free flowing river is not necessarily restoration of the river's original state.
One thing that may be necessary as a long term plan, would be to change limits to beaver trapping. Currently, the limits are take what you want as long as they don't get extirpated. The limits for trapping would be better if the take was based on the amount of beaver that should be present in a specific area, which is generally, at this time, a lot more than what is there. Unlike other game and fur animals, beaver do modify, improve and create habitats for other species...and canoeists. I don't have any big problem with trapping, but it does annoy me when some guy goes in and takes out beaver that are doing a helluva lot more good than what's gonna come out of selling a beaver pelt. They a have a real knack for taking out breeding colonies just as an area is being colonized, instead of waiting for a healthy population to get established.

I did an artist residency in the Clackamas Wilderness (western Oregon) where I was mapping bottom land near the river. After a day or two, I wandered out into a big (1/4 mile x a short 1/2 mile) open and rocky clearing that didn't make any sense in a forest of 180 ft tall old growth Doug Firs. It hadn't been logged. Mostly, the opening was brush and some alders, but there was a little mound with a few full size fir trees. It took me a couple more days before I figured out that there was a very long and very old beaver dam rimming the clearing just inside the edge of the forest, and the mound with the fir trees had been an island, and I was walking around in an big old beaver pond. That pond had been there long enough that there weren't any dead snags, but not so long to become a meadow, and it drained recently enough that it was still in the first stage of reforestation (alders).
 
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All the dams around me in the Midwest were built to run mills of various types which are all long gone. They're small concrete low head dams. When first built all those years ago they created small "ponds" in the upstream side but now they're all silted in.

Some were broken up, either intentionally or unintentionally, many years ago and are a bit of a jumble that allows water to pass through at all water levels. Other dams are still solid and taller. These have been being removed over the past few years.

They often install a series of rock bars upstream from the dam to stair step the water level after removal.

It doesn't make a huge difference for recreation but I'm sure the fish, and even more so the mussels, appreciate it.

A few small dams create small lakes near my house. I'd be happy to see the dams removed and the lakes go back to being shallow sloughs as the were historically. I doubt it will ever happen as I'm probably in the minority other than duck hunters.

Alan
Three dams have been removed on the DesMoines. One South of Humboldt ( Corn Belt ) Two in Fort Dodge. No more drownings from those dams.

Jim
 
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