$568 million upgrade of the Gilboa Dam finished

GILBOA—After two decades of planning, design and construction, a $568 million upgrade of the Gilboa Dam at the Schoharie Reservoir is now completed.

The New York City Department of Environmental Protection (DEP) celebrated the work’s conclusion on Friday along with the centennial anniversary of the city’s Catskill water supply system.

“In completing the modernization of the Gilboa Dam, we are strengthening the engineering marvel built by past generations, preparing it for the challenges of our changing climate, and ensuring that millions of people can continue to enjoy safe, high quality drinking water,” said DEP Commissioner Lisa F. Garcia.

The upgrades bring the system’s northernmost reservoir up to modern standards and will allow it to serve New Yorkers for the next 100 years, according to Garcia.

Work included reinforcement of the dam with 234 million pounds of concrete, rehabilitation of the inlet to the Shandaken Tunnel, and construction of a new high-capacity drainage system—called a low-level outlet—that can empty the entire reservoir in under two weeks and enables DEP to control the water levels.

DEP also planted more than 100,000 trees and shrubs and added a public overlook with displays of Gilboa fossils―nearly 400 million year-old petrified tree stumps from one of the oldest known forests on earth.

“This milestone highlights the significant progress made as the DEP and local communities have come together to work side by side in our mutual interest,” said Schoharie County Board of Supervisors Chairman Bill Federice.

“The open communication has resulted in increased cooperation between the DEP and the watershed community, a partnership we look forward to continuing,” Federice said.

Back in 1905, the New York State Legislature passed a law allowing New York City to acquire land to build dams, reservoirs and aqueducts in the Catskills to meet its growing water demand.

Work on the Catskill system began in 1907 with the 92-mile-long aqueduct to bring water from the planned Ashokan Reservoir in Ulster County to the city. In 1917, with the aqueduct and Ashokan, Kensico and Hillview reservoirs complete, Catskills water reached New Yorkers in all five boroughs.

But the city wanted more water and that same year acquired the now flooded village of Gilboa, along with more than 2,000 surrounding acres. Homes and businesses were razed, graves were relocated, and some 350 people were forced to move.

The 18-mile-long Shandaken Tunnel, to carry water from the Schoharie Creek to the Ashokan Reservoir, was built and during the summer of 1926, workers sealed the Gilboa Dam, allowing the Schoharie Reservoir to fill for the first time, holding roughly 20 billion gallons of drinking water.

The original dam cost $7.8 million to build by the time it was put into service in 1927. It measures 2,024 feet long, 182 feet high, and more than 150 feet wide at its base.

Today, the DEP-managed water supply―comprising 19 reservoirs and three controlled lakes―provides approximately one billion gallons of drinking water each day to nearly 10 million residents, including 8.3 million in New York City.

Previously, a $138 million reconstruction of the Gilboa Dam was completed in 2014.

DEP began an investigation into the integrity of Gilboa Dam after the flood of 1996, which overtopped the spillway by 6.7 feet―a record until 2011 when Hurricane Irene sent roughly eight feet of water over the dam’s spillway.

An initial investigation, completed in 2003, found that Gilboa Dam would require comprehensive rehabilitation and upgrade because it likely did not meet modern standards for dam safety. Additional engineering work in 2005 found that the dam could collapse under extreme weather conditions, according to the Association of State Dam Safety Officials (ASDSO).

If that happened, many residents would have only minutes to escape. The villages of Schoharie and Middleburgh would be submerged under 30 to 40 feet of water, and floodwaters would carve a path of destruction up to 60 miles long, the ASDSO reported.

Following that report, DEP moved immediately to make emergency and long-term repairs.

“With the completion of this $568 million upgrade to the Gilboa Dam, we are protecting one of the finest water systems in the world and delivering the best-tasting water the country has to offer for millions of New Yorkers,” said New York City Mayor Zohran Mamdani.

“The water that flows from our taps is only possible because of generations of public investment, extraordinary engineering and deep partnership between New York City and communities across New York State,” Mamdani said.