By definition, a dam is “a barrier preventing the flow of water or of loose solid materials such as soil or snow”…so why does Union City Dam sometimes look like there’s no water in it?
That contradiction is by design: Union City Dam is the only “dry” reservoir in the U.S. Army Corps of Engineers Pittsburgh District.
For much of the year, there is little to no water at the reservoir.
Passing by the dry-bed reservoir causes some people to think the dam is broken.
Although the reservoir does not maintain a permanent water pool, the dam functions as designed to retain excess water during rainy seasons, Union City Dam exists to control flooding. Much like the rest of the dams operated by the Corps of Engineers, with one exception -- it is entirely self-regulated.
Because of its design and purpose, Union City is unstaffed. Unlike the other 15 reservoirs within the district, a park ranger or maintenance worker visits the control tower each morning to check or adjust the water flow.
The dam works without any gates or machinery, Water passes through a conduit invert at the bottom of the dam at a steady rate. It was built in 1971 to control the frequently-flooding French Creek.
Megan Gottlieb, the district’s water management unit lead, describes the dam like a colander: if too much material pours into a colander, the colander will temporarily back up. When too much water flows into the reservoir, the riverbed turns into a lake, which helps the dam control the water release amount.
During heavy rain, the dam releases water via its spillway crest once the pool’s elevation eclipses 1,254 feet above sea level. The spillway crest does not require manual operation, just like the conduit invert. The water release is automatic once it surpasses a specific elevation.
The pool elevation can reach 1,277 feet before overtopping the spillway. Since its construction more than 50 years ago, the water level has not overtopped the spillway.
“Without Union City Dam, the French Creek would be a large, uncontrolled tributary to the Allegheny River,” said Gottlieb. “Even though the dam doesn't have gates, it still provides flood risk management because it's there.”
Union City Dam in Saegertown, Pennsylvania, is only 25 miles away from Woodcock Creek Lake, also owned and operated by the Pittsburgh District. One crucial distinction between the two, aside from Woodcock Creek Lake using gates and other machinery, is the two facilities’ drainage basins.
A drainage basin is the area of a watershed that drains into a reservoir and changes based on topography. Union City Dam’s drainage basin is about 222 square miles, extends into southwestern New York and feeds into French Creek. The creek flows downstream to Woodcock Creek Lake, which has only 46 square miles of drainage basin.
The reservoir’s design funnels those 222 square miles of water into the French Creek, mitigating flood risk for areas between the dam and Woodcock Creek Lake.
Union City Dam sees several unique wildlife benefits because of its location and dry-bed conditions.
“The dam is a unique project in the sense that one minute the waters might be a lake and one minute they return to a stream,” said Carl Nim, a biologist with the district’s Water Quality Team. “It provides different flow regimes and habitats for fish and amphibians. Smaller fish species are beneficial for the broader ecosystem.”
According to Nim, the area’s forestation and lack of industry mean the dam can act more like a natural river system and contribute to the French Creek watershed.
“French Creek was named the 2022 River of the Year by the PA Environmental Council,” said Ryan Hill, the supervisory natural resource management specialist at Woodcock Creek Lake. “French Creek contains 27 of Pennsylvania’s 65 freshwater mussel species, four of which are federally endangered. It's a unique water system Union City Dam contributes to.”
Hill’s office at Woodcock is 30 minutes from Union City Dam, but he is dual-hatted to oversee both reservoirs. Hill and his staff visit Union City Dam weekly to ensure the dam is functioning correctly.
As a Jamestown native, Hill grew up near Woodcock Creek Lake. Hill sought to return to his ‘biological roots’ and joined the Corps of Engineers in 2021 after earning a bachelor’s and master’s degrees in conservation and wildlife biology.
“One of the first things I learned here is every day is different,” said Hill. “You have to be adaptable, but the bottom line is we’re here to do the best job we can for the public. That’s everything from being fiscally responsible, caring for the area’s natural resources and exploring ways to improve visitors’ experiences.”
Union City Dam has several projects and enhancements on the horizon. According to Hill, his team recently wrapped up a long-overdue entryway-paving project. Next, they are paving a roadway, installing a playground, adding concrete cornhole boards, and establishing several wetland potholes for wildlife in the project’s footprint.
“The sky’s the limit,” said Hill.