Truesdale Lake  

South Salem, New York

Drawdown: Report 11

These are some of the email reports and communications from Scot Evans from Truesdale Lake, James Gorman from Pond & Lake Connection, and others involved with the project. Putting selected parts up here for all to see what some of the discussion and learning is looking like.

Summary: This four-week report involved so many environmental changes that I had to wait to complete it until a break in the weather – the dry spell we’re experiencing – now in its third day. We received so much rain this month that the lake level rose 38 inches after receiving five inches of rain and Snow/Ice Water Equivalent (SWE), even with all siphons flowing much of that time.

When flowing, all three siphons draw nearly 12 million gallons of water out of the lake each day, so you can imagine how much water must flow in to continue increasing the lake level even while they are working.
The lake is now frozen, so we can observe what happens next when the water is pulled out from below the ice. If the ice doesn’t melt during the upcoming 40-degree days, it may start to cave in under its own weight through the air spaces up to the three-foot target depth. This may make access to the middle of the lake for ice skating and ice fishing rather challenging. 

On the up side, if the ice cap over the siphons descends with the lake, it may help to prevent the whirlpools above the siphon intakes that form when target depth is near (see photo). 

Siphon Whirlpool beginning to expand

You have probably noticed that the lake rose to its maximum level of three inches above the spillway ramp elevation a few days ago, even with all the siphons flowing. Once again, this demonstrates that we’ll have no difficulty filling the lake back up in the spring as water flows from West Mountain heights down to our oasis.

LG +0.3

The small 6” siphon continued flowing all by itself during the first two weeks of this reporting period. When the lake level rose from target depth to 2.8 feet below the spillway on December 1st (photo below), we requested that P&LC return to restart both 12″ siphons when the lake rose one more foot, which occurred ten days ago. P&LC restarted both 12″ siphons right on schedule – on the 10th & 11th of December – to keep up with the inflow. They will continue working until the 3-foot target depth can be reached for the fifth time.

LG -2.8 on 12-1-2019

While trees are without leaves, I’ll arrange a visit to Ridgefield Academy to take a photo of the lake from West Mountain and post it on NextDoor and in the next report so all can see that we live in a watershed valley.  

Rain Total30 YR AVG3 ft target depth achievedLake freezes completely
SEP 0.6″ 4.5″1st – Sunday 9/22
OCT7.4″4.6″2nd – Monday 10/7
NOV3.1″4.4″3rd – Tuesday 11/71st – Sunday 12/8, then melts
DEC5.3″ (to date)4.1″4th – Friday 11/292nd – Friday 12/20 solid

When December ends in ten days, rain and SWE may match last year’s wet December that totaled 6.33 inches. Today, with all siphons flowing, the lake level is two inches below the spillway ramp and descending.

Daily Observations:

Precip as of Winter Solstice in 2019

TUE     11/26        LG -2.5        Outflow exceeds inflow with all siphons flowing.
 WED    11/27        LG -2.7′       Outflow exceeds inflow with all siphons flowing. 
THU     11/28        LG -2.9’       Outflow exceeds inflow where the west 12″ siphon shuts down naturally.
FRI       11/29        LG -3.0’      Target Depth is achieved where the east 12″ siphon shuts down naturally.
SAT      11/30        LG -2.9’       Inflow exceeds outflow with only the 6″ siphon flowing.
SUN     12/1          LG -2.8’       Inflow matches outflow as Winter Storm Ezekiel approaches.
MON    12/2          LG -2.7’       0.77″ rain where Inflow matches outflow.
TUE      12/3         LG -2.5’       0.20″ rain where Inflow exceeds outflow as coastal low pressure cell 
                                                 moves in with steady light rain.
WED     12/4         LG -2.4’       Inflow exceeds outflow.
THU      12/5         LG -2.3’       Inflow exceeds outflow with salt added to each siphon frozen discharge.
FRI       12/6          LG -2.2’       Inflow exceeds outflow.
SAT      12/7          LG -2.2’       Outflow matches inflow.
SUN     12/8          LG -2.2’       Outflow matches inflow where 100% lake is frozen.
MON    12/9          LG -2.1’        0.37″ rain where inflow exceeds outflow where lake ice completely melts.
TUE      12/10       LG -1.3’        0.88″ rain where inflow greatly exceeds outflow with heavy rain. 
                                                  P&LC restarts both 12″ siphons. (east shuts down)
WED     12/11       LG -1.3’        0.58″ rain where Inflow exceeds outflow after receiving 0.87” rain.
                                                  P&LC restarts east 12″ siphon.
THU      12/12       LG -1.3’        Outflow matches inflow with all siphons flowing well.
FRI       12/13       LG -1.3’        Outflow matches inflow with all siphons flowing.
SAT      12/14       LG -0.5’        1.47″ heavy rain where inflow greatly exceeds outflow and all siphons flowing.
SUN     12/15       LG -0.2’        0.7″ light rain where inflow exceeds outflow with all siphons flowing.  
MON    12/16       LG 0.1’       Level rises over spillway ramp for the first time this drawdown.
TUE     12/17       LG 0.2’’       Inflow exceeds outflow with all siphons flowing.             WED    12/18       LG 0.2’’       Inflow matches outflow with all siphons flowing.
           THU     12/19       LG 0.1’’       Outflow exceeds inflow with all siphons flowing.
           FRI      12/20       LG 0.0’’           Lake level descends to spillway ramp height. 
           SAT     12/21        LG -0.1’’        Outflow exceeds inflow with all siphons flowing.

           SUN     12/22       LG -0.2’’        Outflow exceeds inflow with all siphons flowing.  

This report is set to launch upon the occurrence of Winter Solstice – at 2319 EST.

Happy Holidays to all,

Should we issue a warning to stay off the ice due to the risk of it collapsing as the drawdown continues?


Hi Lara,

Good question and there are two aspects to consider here. 

The first aspect is considering the effect of the drawdown with regard to the ice. The ice cannot support it’s own weight since it is flat and not shaped like an arch. The ice sheet will descend with the lake from the center out toward the perimeter. The air pockets and stress relieving ice breakage will occur in the perimeter areas where the exposed lakebed is already documented. The only risk to the resident is in navigating the broken ice and craters in order to get beyond the exposed lakebed perimeter on the way toward the center for good skating and ice fishing. So the risk for 90% of the lake will be the same as it has always been. Passing along this information may be better than issuing a warning to stay off the ice altogether, unless the board is concerned with potential liability. 

The second aspect is the classic monitoring and reporting of ice conditions so residents can make their own decisions as well as assume the risk for skating or ice fishing. 

Meghan Crystal has posted a question about ice conditions on NextDoor. So regarding your question above, I’ll answer with a post about today’s conditions only. Please let me know if you want to post a caution regarding the future or if you want me to.


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