National Infrastructure Week: DEP Celebrates “Holing Through” First Section of New Release Tunnel

Micro-tunneling machine breaks through to complete land leg for new release works

The release works are one component of a larger $400 million program that has strengthened infrastructure and will improve operational flexibility at Schoharie Reservoir, which annually supplies about 15 percent of New York City’s drinking water. The program began with the full-scale rehabilitation of the 155-foot tall Gilboa Dam, which was completed in 2014.

The $138 million Gilboa Dam reconstruction – completed well ahead of schedule - was named an ACEC-NY Engineering Excellence Diamond Award winner and National Dam Rehabilitation Project of the Year by the Association of State Dam Safety Officials.

(NEW YORK, NY – May 22, 2018) – The New York City Department of Environmental Protection (DEP) reached a landmark recently when a micro-tunneling machine broke through a wall of rock and completed the first leg of a new release tunnel at Schoharie Reservoir.

The “holing through” happened April 23 at 9:02 p.m. It marked end of tunneling for the 930-foot land leg of the tunnel.

Engineers will now focus on building the 1,188-foot water leg of the tunnel, which will extend from a shaft near Route 990V in Gilboa, NY and come up through the bottom of the reservoir.

The milestone is part of a $142 million project to build release works at the reservoir. The new tunnel is expected to be complete in about three years. It will give DEP the ability to release water downstream of the reservoir into Schoharie Creek to facilitate dam maintenance, respond to potential emergencies, mitigate flood risk for downstream communities, and enhance downstream habitat for fish and wildlife.

The release works are one component of a larger $400 million program that has strengthened infrastructure and will improve operational flexibility at Schoharie Reservoir, which annually supplies about 15 percent of New York City’s drinking water. The program began with the full-scale rehabilitation of the 155-foot tall Gilboa Dam, a $138 million project that finished in 2014. It will also include upgrades to the Shandaken Tunnel Intake Chamber and site restoration work. DEP implemented the program of repairs and upgrades at Schoharie Reservoir more than a decade ago to achieve modern safety standards at Gilboa Dam.

The machine will drive two tunnel sections that total 2,118 feet, running as deep at 185 feet below the surface. The recently completed land leg of the tunnel stretched 930 feet from the gate shaft to a valve chamber on the eastern bank of Schoharie Creek. The valve chamber is located about 1,000 feet downstream of Gilboa Dam. A second leg of the tunnel—set to begin construction soon—will run 1,188 feet from the gate shaft to the intake structure at the bottom of Schoharie Reservoir, several hundred feet south of the dam. Once workers bore into the bottom of the reservoir, a specialized dive team will remove the micro-tunneling machine from the 135-foot-deep water and install the remaining parts of the intake structure.

Gilboa Dam was built from 1919 to 1927 and impounds Schoharie Reservoir, the northernmost reservoir in the City’s water supply system. Schoharie Reservoir can store up to 19.6 billion gallons of water, and it accounts for nearly 15 percent of the drinking water delivered to New York City each day. Schoharie Reservoir collects water from a 314-square-mile watershed. It diverts that water through the 18-mile Shandaken Tunnel, which discharges into the Esopus Creek where it travels another 11 miles before entering Ashokan Reservoir. From Ashokan Reservoir, the water flows south through the 92-mile-long Catskill Aqueduct to New York City.

For more information, visit the DEP website.

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