Thursday, January 24, 2013

Ice Jams and the Winooski River

What: About a year and a half ago, we were faced with severe flood warnings up and down the state. Irene didn't disappoint and wreaked havoc with both flash floods and sustained flooding events. The day after the storm the air was thick, but quiet, when I went down to the Salmon Hole (just downstream from the dam in downtown Winooski). I took the photos from the bridge on Colchester Ave looking west towards Salmon Hole. They definitely don't really do justice to how absolute and immense the power of that water was.

It's full on winter (Happy coldest day of the year!) and to celebrate I thought I'd head down to the river  to retake photos from the same perspective as I did during Irene. What a difference! Upstream there are a few patches that are open, and there's a frozen waterfall. Somehow we're faced with flood warnings once again; residents in Franklin Co. NY have even been evacuated.

Ecological notes: Ice Jams are not uncommon, and occur on all different scales (you can get an ice jam in a gutter). There are a few types of ice jams, as I'm learning, and the warning is for freeze-up jams. The flood warnings are caused by the excessively cold weather we've had. The cold weather will rapidly freeze the surface water of rivers that haven't frozen over yet (sections of the Winooski, Lamoille, etc.). Surface flow will break off chunks as they freeze and send them downstream. These frozen rafts of ice can get hung up on snags, and any other obstruction. If enough of that ice starts to accumulate it dams up the water. The thicker the ice the better it acts as a dam. If and when those dams burst, they'll release all their water at once, which can cause devastating flooding downstream (as it did in Eagle, Alaska in 2009).  Here's a video from Woodsville, NH of the flooding caused by an ice jam that broke. You can imagine how destructive those chunks of ice would be to trees, houses, etc. along the way.

Where: Salmon Hole @ Winooski River

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