In the fall of 2009, an announcement in the newspaper of planned maintenance to the existing Rainbow Hydroelectric Plant Dam on the Farmington River in Windsor, CT, was news I had been waiting to hear for many years. This activity would dramatically lower the water in the reservoir that the dam impounds and to my knowledge would reveal a scene that hasn’t been visible since 1976 – the remains of the Oil City Hydroelectric Dam.

Photo 1: Oil City dam and powerhouse remains, 1976. Richard Daley Photography, Inc., Windsor Historical Society collections 2010.58.28.

Photo 2: Powerhouse remains, 2009. Photograph by the author, WHS collections 2010.58.30.

Photo 1

When the present 60-foot high Rainbow Hydroelectric Dam was built in 1925, the large reservoir it created submerged the older Oil City Hydroelectric Dam built in 1890-1891 a quarter of a mile further upstream. An April 12, 1890 article titled A Great New Project announced the building of the original dam and electric power plant. It was to be a 27-foot high dam providing power to Hartford to light streets and power motors in factories there at great cost savings. The plant produced 2,000 horsepower a day. The Oil City dam and the hydroelectric equipment was used to generate and transmit electric power over copper wires eleven miles to Hartford. In these pioneering years of electric power use, this plant also served as a laboratory for experiments with different electrical frequency and phase generation. This 1976 image shows the Oil City dam’s timber and trap rock that impounded the water and its powerhouse remains below the dam. These are normally submerged underwater. The photo was taken from the bottom of the dam looking upstream on the Farmington River on the Northwest Park side of the Reservoir.

Photo 2

During the month of September 2009 when the water receded, the submerged remains of the Oil City Dam and hydroelectric complex could be viewed again and compared to photos taken in 1976. The comparison reveals that the remains have deteriorated. In Photo 2 there is a noticeable difference where you see what appears to be a roof or floor above the powerhouse’s turbine/generator assembly that has collapsed to a greater degree. The powerhouse burned in 1897. A Hartford Courant article dated September 7, 1897 detailed the story. The fire broke out at 2:30 in the morning because of short circuited wires. The powerhouse burnt to the ground and Hartford’s downtown experienced a power outage but for only fifteen minutes. The outage was so short because the Hartford Electric Light’s former steam powered Pearl Street plant was brought online to provide the needed power until the hydro plant was rebuilt. The article also stated that if additional power was needed because of the outage, there were big storage batteries at the rear of the Courant building.

Photo 3: Sliding input gate remains, 2010. Photograph by the author, 2010.58.32.

Photo 4: Penstock remains, 2010. Photograph by the author, 2010.58.33.

Photos 3 & 4

I took many photos of the submerged remains but the two that I think are most interesting and perhaps the first time ever photographed are Photos 3 and 4. Photo 3 shows a sliding wood input gate in the arched cavern at the bottom of the impounded Northwest Park side’s stone abutment. When this input gate was opened, it allowed water to flow in the penstock and turn the turbine/generator remains seen in Photo 4. A penstock is simply a conduit to channel water. With a 27-foot head of water, one can imagine the tremendous and efficient hydraulic force that went through gate to feed that turbine. It was a remarkable engineering accomplishment in its day.

Photo 5: Oil City dam under construction, 1891. WHS collections 2009.1.9.

Photo 5

This 1891 view shows the dam under construction. It was taken slightly downstream from the dam’s abutment and reveals the logs and trap rock that made up the dam and impounded the water.

Photo 6: Abutment remains, 2009. Photograph by author, 2010.58.31.

Photo 6

I took this image in 2009 slightly upstream from the dam’s abutment. It shows that the logs and trap rock are still holding up well. The submerged logs are over 120 years old and well preserved. The trap rock used possibly came from the abundant basalt quarries on nearby Metacomet Ridge.

At the conclusion of the Rainbow Dam’s repairs in 2009, the great watershed of the Farmington River soon refilled the Reservoir and now only the Oil City stone abutments are visible. Submersion will help preserve these remains. Perhaps in many years to come the Reservoir’s impounded water will be again drained and the thrill of seeing the remains between the abutments will once again be a treasured event for industrial archaeologists.

Rainbow Reservoir can be reached by a short hike in Windsor’s Northwest Park or by boat from a state boat launch in the Rainbow section of town.

By Jim Trocchi, volunteer.
Top image: the Oil City dam before 1897. WHS collections 1954.2.6.42.


  1. Roth, Matthew. An Inventory of Historic Engineering and Industrial Sites. Society of Industrial Archaeology, Houghton, MI, 1981.