Historic Mills of Connecticut

Companies Associated w/Complex

• Connecticut Light and Power Co. 1929-2000

Use (Historic)

• Other: Power generation

Largest Documented Workforce

n/a

Historic Narrative

Rocky River Hydroelectric Plant was one of the first pumped-storage hydroelectric plants in the United States, and the largest such facility in the country when it was completed in 1929. Water is pumped from the Housatonic River into the reservoir and the same water flows back down from the reservoir through the turbine to generate power. It takes 1.63 times as much energy to raise water into the reservoir as is generated from the same water on its return to the river. This apparently irrational system made economic sense only when inter-connection of electric generation and transmission systems over large areas made it possible to use power from other plants, during off-peak hours, for pumping. Steam plants were run throughout the night even though demand was quite low, so energy for pumping was obtained there. Power for night-time pumping was obtained from hydroelectric plants during the spring, when runoff water exceeded normal demands for electricity at night. Thus, pumping was done with low-cost, off-peak energy and energy from the stored water was released at peak-load periods when it was at a premium. The plant still produces electricity with mostly original equipment. (Roth)

Number of Existing Buildings

One (1) block.

Dates of Construction

1929

Architect

n/a

Builder

n/a

Building Type

• Powerhouse

Architectural Description

Connecticut Light and Power Co. hired U.G.I. Contracting Co. of Philadelphia to design and build the facility. The plant sits on the bank of the Housatonic River at its confluence with the Rocky River, which was dammed to create the storage basin. An earthfill dam (100' high, 925' long, 525' wide at the base) was built and smaller dikes were raised at low points in the surrounding hills to create Lake Candlewood, at 81.3 square miles the largest lake in Connecticut. A half-mile long canal leads to a wood-stave penstock (943' long, 15' inside diameter). The wooden penstock carries water to a steel surge tank (76' high, 9' inside diameter) and steel penstock (672' long, inside diameter reduces from 15' to 11') which runs downhill to the power house, where an S. Morgan Smith single runner horizontal turbine, under 226' head, drives the single General Electric generator. The 105' x 40' brick powerhouse also contains two motor-driven Worthington centrifugal pumps, which are used to fill Lake Candlewood. Water pumped up travels through the same structures (except the turbine) through which it will flow back down when used for generation. (Roth)

Exterior Material(s)

• Brick

Structural System(s)

n/a

Roof Form

n/a

Roof Material

n/a

Power Source

• Hydro-Electric

Condition

n/a

Condition Notes

n/a

Specific Location

One 33 acre parcel between the Housatonic River to the north and Kent Road to the south

Adjacent To

• Water (for Power)

Exterior Visible from Public Road?

Yes

Parcel ID / Assessor Record Link

• 34/31/1 / Link →

Acreage

33.0

Use (Present)

• Industrial

Form Completed By

n/a

Date

n/a

Bibliography

1. Roth, Matthew, et al, Connecticut: An Inventory of Historic Engineering and Industrial Sites (Washington DC: SIA, 1981).