Truesdale Lake  

South Salem, New York

Drawdown: Report 8

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: Harold Ossher’s conclusion, following his evaluation of watershed research and flow data collected, was to use two 12” siphons plus the one prototype 6” siphon. This proved sufficient to stay ahead of this year’s wet October 8.2” rainfall total. (Average rainfall for October over the last three years is 7.7″ where OCT 2018 was 4.6” and OCT 2017 was 10.3″.)

When drawdown depth is achieved once again, I will gather the measurements of the siphons constructed on scene so that Cliff Munz can revise and convert my design drawing to CAD. 

Thursday 10/31/19 brought us a wicked double cold front for Halloween, delivering 1.01” of rain over 28 hours with strong wind gusts. In advance of the storm, James Gorman of P&LC restarted the west 12” siphon at 0930 EDT ~ providing a well timed response before the rain accumulated, before inflow exceeded outflow and before the two cold fronts passed with freezing temps. All three are flowing again at 1,100 CFM and the cause of the 12” shutdown was not identified. The lake gauge reading at restart was 2.2 feet below the spillway. 

Following the last report, the lake gauge was -2.0’ and ended the week nearly one foot lower at -2.9’ with siphon flow exceeding inflow after the 1.15“ of rainfall we received for the week.

Lake gauge at -2.0′
Last week’s rainfall
Oct 2019 rainfall

Daily observations
TUE   10/29      LG -2.0’     Rob Cummings consolidates all reports, photos & responses to the lake’s website: in order to keep everything out in front of the inevitable questions.

WED  10/30      LG -2.1’     A steep pressure, temperature, & humidity gradient cold front approaches from the west.  THU   10/31      LG -2.2’     James Gorman restarts the west 12″ siphon ahead of the storm.. All siphons flowing.

FRI      11/1       LG -2.1’     LLR from 1.01” rain received. Inflow exceeds outflow. 

SAT     11/2.      LG -2.2’    30° F with first frost of the season. Outflow exceeds inflow for remainder of the week. 

SUN    11/3.      LG -2.4’     A long stick is caught in the east 12″ siphon intake, but it is still drawing water.

MON   11/4.      LG -2.7’     Whirlpool increases in diameter over west 12″ siphon intake which is shallower than the east siphon. This is still flowing but will shut down first.

Good morning Harold,

Here is my precip report for this year which includes JAN through SEP for a total of 37” (plus the 8” we received in OCT).

The report also shows the 30-year average for each month. (The thirty year average for OCT is 4.6” and we received 8.2” this past OCT, making your siphon determination of two 12” + one 6” right on target!)

I listed the links in preference order with your favorite format first.


Many thanks, Scot, great to have this data.
BTW, I was wondering whether fins at and extending a bit beyond siphon intakes, like the bottoms of rockets, would help with the whirlpools? On the other hand, I think we reached target depth with the large siphons still running, so we might not want to keep them going longer.
– Harold

Hi Harold, 
This would very likely work to prevent whirlpools from forming above the perfect circle at the intake heads. I wonder if there exists such an attachment for PVC pipes. Maybe James will fabricate and patent his invention! Here are the baffle diagrams for rocket engine nozzles:

[. images did not download for me 🙁 .]

And you’re right, this would be a future consideration for James to consider for siphon improvements to our next drawdown attempt. 

He luckily installed the 12” intakes deeply enough so that the whirlpools shut them down right at target depth. The deep 6” siphon is still running and will help to keep up with the winter inflow and possibly enough to maintain the lake level close to target depth. 

If we get a lot of NOV rain and if inflow exceeds the effectiveness of the 6” siphon, I’ll ask James to restart the two 12 inchers. 

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