ELLSWORTH — A defective electronic sensor, melting snow and heavy rain last week led to the high water flows in the Union River that flooded Shore Road last week and through the weekend.
On Tuesday night last week, a submerged electronic transducer that monitors water levels at the Graham Lake dam failed, Samantha Edwards, a spokeswoman for dam owner Brookfield Renewable Energy, said Monday afternoon. That allowed water in the lake to rise to more than 105 feet above sea level, about 1 foot higher than the maximum 104.2 feet allowed under the dam’s federal license.
“We had a crew at the dam the Friday before [Jan. 19] and everything was fine,” Edwards said.
According to Edwards, the transducer at the dam measures water pressure, which increases with water depth, and sends a signal to the company’s national system control center in Marlborough, Mass., near Boston. Operators at the Massachusetts site are able to open and close gates in the dam to control water levels in the lake.
Last Monday and Tuesday, Brookfield began getting phone calls from area residents about rising water levels. Edwards attributed the increased water level to recent heavy rains and snow melt.
Despite the phone calls, “everything was reading normal, as it should,” at the control center, Edwards said.
Though the readings looked normal, the water level was more than a foot higher than indicated. After investigation, Brookfield workers replaced the defective transducer last Wednesday.
“We’re still looking into how the transducer failed,” Edwards said Monday morning.
Even after replacing the transducer last week, Brookfield “had people on site” at the Graham Lake dam Wednesday and Thursday night, and again through the weekend, Edwards said, to monitor the situation.
According to Edwards, local Brookfield employees do “weekly checks” of the Graham Lake and Leonard Lake dams. During the winter, locally based crews check the dams “a couple of times a week” in Ellsworth and elsewhere in Maine.
Brookfield owns about 50 dams in Maine, including several that create water storage rather than generate hydroelectric power.
On Monday morning this week, the water level at Graham Lake was 103.3 feet, about 8.4 inches below the legal maximum.
“Our first priority is getting the elevations correct,” Edwards said.