Re: [Paddlewise] "Refurbished Lowhead Dams"

>>Hey, Joe P.
>How was yours "refurbished?"
>
    Originally it was a 200 ft wide dam about 4-5 ft nearly vertical drop
over it. I posted a photo it on the NE Paddlers' Message Board under
"Safety" if you want to look at it.  So you had a strong recirculation with
the backwash returning from nearly 20-30 ft out.  To make it even worse,
there were tiny spillways at each end so if you had worked your way to the
shore the current would push you away.
    The modifications consisted of nesting gabions (wire cribs filled with
rock) installed as steps across the face of the dam.  This formed a gentler
slope and far less recirculation.  I think they also put some gabions below
just there to break up the recirculation.  I still wouldn't run this, but I
think you'd now have a chance to escape it.
    What we didn't know until the reconstruction was being done was that the
engineers had originally installed a low wall completely across the river
about 100 feet downstream.  As it was underwater, it actually Increased the
backwash, elevating the boil line about a foot above the normal water level.
You can see this in the posted picture.
    Why they did this is unknown, but it sure made for a very efficient
killing machine.  The dam was intended to hold back water for the intake of
a water treatment plant.  There is also a fish ladder here and perhaps
someone thought the low wall would offer a quiet spot for fish to regroup
before heading up/down the ladder.
Joe P.


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