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  •  Rollers are (7+ / 0-)

    on the dam.  The water flows over them in a regulated way to keep river levels right for river traffic, etc.  I'm not sure how they do that, but when they are up, the river is free-flowing.  Right now the current is somewhere between fierce and maniacal.

    Here's more info and a pic.  The rollers are the reddish things.  If you click on the pic, you can get a better view of the water tumbling out from them.  This is what makes us prime real estate for eagles in the winter and pelicans in the summer.  They hunt the stunned fish emerging below the dam.

    -7.62, -7.28 "Hold fast to dreams, for if dreams die, life is a broken winged bird that cannot fly." -Langston Hughes

    by luckylizard on Fri Apr 19, 2013 at 03:04:21 PM PDT

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    •  We have lots of dams around here, but I've (6+ / 0-)

      never come across a roller dam before, or any mention of that. Learn something new every day. Sounds like their primary function is to minimize turbulence downstream to limit erosion, which must be a bigger problem on the Mississippi than the Columbia. Very interesting engineering. The description of them as a "washing machine of death" is a bit alarming. Under a dam wouldn't be my first choice as a swimming spot anyway. I can see why the fish would get stunned. Do they ordinarily go to and fro through the locks?

      Regardless, those pictures give a real sense about how much water you're talking about. I'd forgotten what a gigantic river it is. Hope it doesn't rise much higher.

      •  I didn't realize until lately (2+ / 0-)
        Recommended by:
        OceanDiver, RiveroftheWest

        that roller dams were not the norm.  I had no idea that ours was the biggest one in the world.  Having lived here all my life, I'd just taken the dam for granted.  

        I'm sure some fish go up through the locks, but probably not nearly as many as go over the dam.  The channel is guaranteed 9ft., which doesn't seem like much for the massive barges that ply the river.  I don't know how deep the locks go, but I do know that there isn't any room on the sides to speak of.  That would limit the exchange of fish between the two sides.

        The upper river has many place that are cut through rocks, forming scenic bluffs.  Beginning just upriver from us, the valley spreads out into a wider flood plain which pretty much continues to the Gulf of Mexico.  

        The map of the U.S. around the LA coast would look quite different (and be ever-changing) without the system of locks and dams.  In fact, the river would probably not enter the Gulf where it does now.  It was in the process of changing course to follow the Atchafalaya River.  That would have left New Orleans and its ports a commerce without the vital connection to the rest of the country.  That was a big factor in the decision to build the dam system.

        How's that for too much information?  :-)

        -7.62, -7.28 "Hold fast to dreams, for if dreams die, life is a broken winged bird that cannot fly." -Langston Hughes

        by luckylizard on Sat Apr 20, 2013 at 06:16:07 AM PDT

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        •  Now I'm curious about fish and your roller dams (3+ / 0-)

          Over here, our anadromous fish (mainly salmon) have to go past dams both ways to complete their life cycle, and dams that block them will cause them to go extinct (like the race of salmon on the Elwha river). Our dams are built for hydroelectric power, and secondarily irrigation, and have a lot of vertical drop, so figuring out a way to get the fish past them has always been a problem, and has not really been solved, even with fish ladders etc. Your dams seem to be mainly for flood control and maintaining channels. I suppose fish could just live on one side or the other?

          •  The dam produces some hydro power, (3+ / 0-)

            for the Rock Island Arsenal, I think, and maybe for the bridge.  Our fish don't depend on a particular route to survive, so making it difficult to migrate upstream isn't quite as big a problem.  No salmon this far from the sea.  :-)  There may be other issues down by the Gulf, but I don't know as much about that.

            -7.62, -7.28 "Hold fast to dreams, for if dreams die, life is a broken winged bird that cannot fly." -Langston Hughes

            by luckylizard on Sat Apr 20, 2013 at 12:02:47 PM PDT

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