Reconstruction of an historic hydro-electric facility that has produced renewable energy for 81 years has been completed. Central Vermont Public Service has finished extensive improvements to the company s Arnold Falls hydroelectric project, located on Mill Street along the Passumpsic River in St Johnsbury. The upgraded concrete structures replace wooden rock-filled, timber-crib dams similar to those originally constructed during the 19th Century for nearby mills. The deteriorating timber dams remain in place, with the new concrete dams just downstream of them to ensure the facility s long-term future.
The federally licensed generating station, which was built in 1928, includes two dams separated by an island. The 180-foot north dam and 60-foot south dam consisted of interlocked logs, which had a limited lifespan due to the riverine exposure and the inevitable decay of wood.
CVPS made substantial repairs to the Arnold Falls dams in the 1940s. In 1976 and 1977, CVPS reconstructed the dams using logs from a local sawmill, and in recent years the company has made ongoing repairs. Compression of rotting logs allowed the crest of the timber-crib structures to settle to the point that more permanent improvements were necessary.
The timber-crib dam structures served as coffer dams during construction. The new dams were built one at a time, starting with the north dam, beginning this past June.
Bancroft Contracting Corp. of South Paris, Maine, did most of the work, under supervision from CVPS Principal Environmental Engineer John Greenan and Area Hydro Station Foreman Frank Chaloux.
The new dams consist of a concrete structure cast in place immediately downstream of the existing timber-crib structures. New flashboards atop the north dam and a crest control system atop the south dam stabilize the water level in the impoundment.
Work on the $1.3 million project was delayed somewhat by heavy rains during the summer, but CVPS officials said they were pleased with the finished work. The facility has produced an average of 1,112,328 kilowatt-hours of electricity annually over the past 10 years.
We expect slightly improved production, possibly as much as an additional 120,000 kilowatt-hours per year, plus improved employee safety and dam operations, spokesman Steve Costello said. Most importantly, the upgrade ensures the continued production of clean, renewable generation at the site for decades to come.
The Arnold Falls facility is one of 20 owned and operated by CVPS across the state. Along with power supply contracts and other generation projects, they help provide CVPS customers with a solid energy value and the lowest rates of any major utility in New England, according to the Edison Electric Institute, and Vermont with the lowest air emissions in the country.
Source: CVPS. 1.6.2010
CVPS completes historical St Johnsbury hydro facility makeover
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