It isn’t often that I update the water level charts more than once a day but I did this day, the water was coming up so fast you could almost watch it rise. The lake has come up a little more than 12″ since last Monday when it started raining, rising from -56.52″ below the top of the dam to -44.16″ earlier this afternoon and they’re forecasting rain for a couple more days too so the lake isn’t done rising by a long shot. Runoff was limited at the start because most of the rain soaked into the dry ground rather than running off into the lake the ground is now saturated and runoff rates are more or less normal now.

You’ll notice a new feature on the water level charts: a straight black line across the chart at an elevation of -34″ below the top of the dam which is the approximate elevation of the bottom of the hole in the dam. When the water rises above this level it will start pouring through the hole. Last year Kelley did everything he could to keep the lake level below -40″ to prevent enlargement of the hole, causing further damage to the dam. If he keeps up this practice this year, expect him to open the gate this weekend.

We’ve finally gotten around to putting current Clary Lake water monitoring data online. It’s a subset of the data collected by David Hodsdon and Jack Holland and will be updated roughly every 2 weeks from early spring through late fall or as often as David and Jack get around to it. What’s online now includes all the data from 2012 and what’s been collected so far in 2013. That little thumbnail at left is what a secchi disk looks like- it’s used to measure the transparency of the water.

• Clary Lake Water Monitoring Data

I hope to get some historical data online soon; there’s quite a bit of it. David has been collecting water quality data on Clary Lake since 1975, Jack Holland since about 2001. Both are certified volunteer water quality monitors. Here’s a typical data sheet from a data collection session and here are 3 charts based on the collected data. Graphing the data is helpful because it allows you to see trends in the data that aren’t necessarily obvious from just looking at it. One disturbing trend evident from the secchi disk chart is that the transparency of the lake water has deteriorated markedly in recent years. This trend also coincides with the increase in phosphorus evident from the Total Phosphorus chart. We’ll be talking more about these trends in the near future.

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Last spring I accompanied David and Jack on one of their regular water quality monitoring sessions and have put together a short photo gallery of that session: “Our Water Quality Monitors at Work“.

Some of you will remember seeing a table something like this last year, on the old site:

These figures were derived empirically which simply means these are based on measurements we made and recorded. They are what they are. They’re averages and on any given day they will likely vary a little or (even a lot) due to changing conditions: lake surface area, the shape of the lake, and most important, the amount of runoff from rain or snow melt. But all things being equal, these numbers should be pretty close most of the time.

Which brings me to the reason for this post: the question of how low can the lake get. I have in the past come to the conclusion that the rock-bottom low water level was somewhere around 6 feet (-72″) below the top of the dam. This figure was arrived at after measuring the water depth at the mouth of the channel at the northwest end of the lake. I also came across a fascinating book entitled “The Water Power of Maine” by Walter Wells, first published in 1869. In it I found a table that I’ve reproduced the table at left. It estimates the additional storage in Pleasant Pond (now Clary Lake) as 4 to 6 feet. Coincidence? I don’t think so.

Yesterday afternoon Colin Caissie and I went over to look a the narrow gauge rail road abutments to assess their suitability for the construction of a coffer dam. To get the distance between the abutments, I waded across the channel (and filled my boots in the process) while dragging a tape measure and found the center of the channel to be 2′ deep. The water level at the time was -54″ below the top of the dam. Adding 24″ to this gives you an elevation of the center of the channel between the abutments of -78″ or -6.5 feet below the top of the dam. The average distance between the abutments by the way is 16.5′. There are more pictures from this adventure in the Spring 2013 gallery.

And there you have it folks. The lake can’t possibly fall more than 6.5′ below the top of the dam and chances are, since there is a gentle slope to the channel on the order of about 1/2 a foot over it’s entire length, the limiting factor likely is the elevation at the entrance of the channel. So if anyone asks you how far the lake can fall, tell `em “6 feet.”

The lake is down -54″ now. It can fall another 18″. Last spring it reached -63″ below the top of the dam. At the rate the lake is dropping, we’ll get there again in 10 days.