Truesdale Lake  

South Salem, New York

Drawdown: Report 9

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: Both 12″ siphons shut down: the west 12” on Tuesday night 11/5/19 and the east 12” on Wednesday night 11/6/19. The 6” siphon was the only one flowing most of this week and it was able maintain the lake level following 0.3″ rainfall with a 2 ½” lake level rise. Lake Gauge started at -3.0′ target depth and ended the week rising to -2.8′. 

Two 12″ siphon pipes dry (right) and 6″ siphon pipe energized and flowing (left).
Hoyt Street lake gauge showing around 2’10” below spillway height.

The intake head of the west siphon is 9” below target depth and the east siphon intake head is 17” below target depth. Both developed widening whirlpools above the intakes and this is likely what shut them down. We need to figure out something that eliminates the whirlpools over the intakes. Internal baffles and external fins are two ideas to reduce or eliminate the whirlpools above the intake heads. External fins in second diagram would be easier to construct and less restrictive to the flow. Experiment with this design first.

External fins with the fin “trailing edges” leading out from the siphon intake head.Experimentation will determine minimum number of fins necessary to eliminate a whirlpool – i.e. eight or fewer fins.
Daily Observations:

TUE     11/05        LG -2.9’        All siphons operating with west whirlpool widening. West siphon shuts down that night.
WED    11/06        LG -3.0′        Target depth achieved once again after the October 10th departure from our last target depth achieved.
THU     11/07        LG -3.0’        Both 12″ siphons have shut down. Scot took measurements of these siphons to provide to Cliff Munz, who is working on a large construction project and cannot convert the siphon design to CAD at this time.

FRI       11/08        LG -2.9’        LLR begins with 0.3″ rainfall. 6″ siphon operating at 125 CFM. 
SAT      11/09        LG -2.8’        Inflow continues to exceed outflow 
SUN     11/10        LG -2.8’        Outflow matches inflow with 6″ siphon flowing

MON    11/11        LG -2.8’         As above. Sue Enos schedules Lake Planning Group Meeting for 11/20/19.

Email from Michael Lombardi, South Salem Fire District Commissioner, regarding the dry well on the north end of Lake Truesdale near Indian Lane and the Dam.

Dear Skip, 

The board of fire commissioners is weighing options to repair and extend the dry hydrant pipe in Lake Truesdale. We have the following questions.1. Will the lake draining program be an annual process or is this the only year it will be done. 2. Is the lake going to be drawn down further. 3. When will the lake be refilled. 

Thank you in advance for your assistance feel free to contact me. 

Michael J Lombardi                                                                                                       Fire Commissioner (914) 588-8270

Thank you for contacting us Michael. We will be planning to do the lake drawdown annually as a way to better control weed growth and overall health of the lake. 

The drawdown is at the expected level at this time with only one smaller siphon running to maintain the target depth with expected normal rainfall. 
The drawdown will last until February 1, 2020 – that’s when we will turn off the maintenance pipe. This is the smaller 6″ pipe which we will use to try to keep the lake level 2.5 – 3 feet below the spillway level. 

After then the lake will fill up with winter snowmelt and spring rain. We anticipate it will be back to regular height by May 1, 2020 and likely well before then.

More information on the drawdown is published on the Truesdale Lake web site -

Thanks for your support,
Skip Jahn

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