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Friday, January 15, 2016

Currents


The BLID installed an aerator in 2002 after a severe winter fish kill.  The purpose of the aerator is to oxygenate the water during the winter to ensure that the fish don’t suffocate from lack of oxygen in the water. 
I always thought that shallow lakes would freeze out when the ice got so thick that there was not enough water left.  That was what killed the fish.  In researching the aerator, I leaned that the real cause is lack of sunlight.  A high snowfall winter is actually more dangerous than a cold low snow winter.  Here is why.  Birch Lake is weedy.  Weeds grow all year long including the winter.  If the weeds have enough sunlight, they grow and produce oxygen.  If the snow and ice get too thick, the sunlight is blocked.  Instead of growing and creating oxygen, the weeds die, rot, and consume oxygen.
So, how effective can an aerator be if Birch Lake is 100 acres and the aerator keeps less than ¼ acre open and oxygenated?  I discussed this with fishing pro and naturalist Larry Dahlberg, the host of Hunt for Big Fish on the Outdoor Channel.   
Larry explained that the aerator would only save the fish within a certain radius of the aerator.  It would ensure that some fish survive and be a spawning stock for the fish population to recover - unless there was a current in the lake.  A current would move the water and carry the oxygen across a larger portion of the lake.
I always wondered if there were still currents in the lake.  Most of the natural water flow was cut off when the construction of Highway 96 separated Birch Lake from the water inflow on the south side.  The construction of North Birch Lake Blvd. cut off the out flow on the north side.
This winter I was able to observe something interesting.  The mild winter and low snowfall has made it easier to see where currents are be operating.   The first thing I noticed is that there is a line of melting snow that stretches from the culvert on North Birch Lake Blvd. to the aerator.
Here is an areal view from over the aerator.  You can actually see the flow lines.


Looking north from the aerator you can see the flow to the culvert on North Birch Lake Blvd.



The flow goes directly to North Birch Lake Blvd.  Sure enough, the water was flowing out of the culvert to the Rotary wetlands.





I also noticed that much of the shoreline adjacent to the Rotary Park wetland was full of water.  The culvert opening is small in comparison to the volume of water attempting to get out.  I began to wonder if the water is flowing out by seeping through the fill of the road. 

On my way over to the culvert I noticed something odd.  There is an in-flow of water from a sping at the Cloisters.  There is a current line from the cloisters to the aerator!









 The following picture is taken from the Cloisters facing south toward the aerator.

 
The last question that came to mind was why would the flow run through the aerator?  The aerator may act as a breather for water movement.  Have you ever poured gas into your lawnmower without opening the breather on the gas can?  The gas does not flow.  When you open the breather it clears the vaacum and lets the gas flow.  I think the opening in the lake caused by the aerator is like a breather.  The ice is putting pressure on the lake.  The water wants to flow out but can’t.  The aerator releases the vacuum and allows the water to flow.
What do you think?

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