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A member of the NHDES prepares a dam for a lake drawdown. Courtesy photo.




Letting it flow
Annual lake drawdowns are planned for October

09/25/14



When New Hampshire’s first dams were constructed in the 1800s and 1700s, most man-made shifts in lake and pond water levels coincided with the needs of mill owners moving their products down the rivers. Often, water levels were lowered for the winter. 

Lumber and other agricultural products aren’t floating down New Hampshire’s rivers anymore, but the state’s Department of Environmental Services still conducts drawdowns of state-owned water bodies every fall, and they still have a purpose.  
“[Drawdowns] started off just for hydropower purposes, but as time went on, the landowners could count on the fact that it would be lower in the winter.” said Daniel Mattaini, NHDES operation and maintenance engineer.
Lower water levels give shorefront landowners a chance to conduct maintenance and renovation projects, including work on docks and retaining walls. They need to know when drawdowns are happening so boats can be stored safely and work can be scheduled appropriately, Mattaini said.
There are about 2,000 dams across the state, and the dam bureau’s three operators conduct drawdowns at about 50 of them. 
“Other lakes that do have drawdowns are owned by municipalities who do the work, and some lakes don’t get drawn down because they have natural outlets, so the water just rises and falls with the weather,” Mattaini said.
For larger dams, the work involves raising a large gate by turning a big crank on top. 
“It’s almost like an old-fashioned barber pole,” Mattani said. “There’s a big screw that picks up a big wooden gate that water passes underneath.”
Instead of gates, smaller dams most likely have “stacked logs” — boards of various sizes with rings attached to them. Operators reach down to those rings with a big metal hook and pull each log out individually.
Determining how fast and when in the fall to drop water levels is a balancing act. The DES tries to drop the water levels at gradual enough rates that animal life has a chance to move to deeper water without being stranded. If it waits too long to get levels low enough, animals that are already hibernating for the winter could be in danger.
On the other end of the spectrum, if water levels come up too soon in the spring, before ice has melted, ice sheets can cause damage to shorefront properties. But officials need to catch runoff from melting snow surrounding watersheds in order to get levels back up by the recreation season.
“We try to keep the water levels down long enough that most of the ice is melted on the ponds,” Mattaini said. 
One lake that wasn’t included on the state’s list of scheduled drawdowns is the state’s largest — Lake Winnipesaukee doesn’t operate like other waterbodies.
“We need a constant release rate in Winnipesaukee because of a hydropower company that has historical water rights that go back before the State of  New Hampshire owned dams,” Mattaini said. 
 
As seen in the September 25, 2014 issue of the Hippo.





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