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Tunnel boring completed at Schoharie Reservoir

Tunnel boring completed at Schoharie Reservoir

Nearly 100-year-old dam has never had regular release system
Tunnel boring completed at Schoharie Reservoir
A tunnel-boring machine is lowered down a 185-foot shaft in the Schoharie Reservoir in 2017.
Photographer: Photo provided

SCHOHARIE COUNTY -- New York City reservoir officials this week retrieved a tunnel-boring machine from the bottom of the Schoharie Reservoir, another step in a $400 million project to install the first regular water release system the nearly 100-year-old Gilboa Dam has ever had.

The installation of the release system will increase protections against flooding for downstream communities along the Schoharie Creek and reduce fluctuations in the creek downstream, benefiting fish and wildlife. The new system will replace a siphon system now used when excess water needs to be released.

The city Department of Environmental Protection retrieved the submersible boring machine from the reservoir on Wednesday, after it earlier had completed 2,118 linear feet of tunnels that will be used to release water downstream. The work was entirely done by engineers remotely controlling the drilling machine.

"The completed excavation and retrieval of this tunneling machine are major milestones in our work at the Schoharie Reservoir," DEP Commissioner Vincent Sapienza said in a released statement. "The net release works and upgrades to our intake structure at the reservoir will provide DEP with more operational flexibility to send the best-quality drinking water to New York City and support the ecological health of the Schoharie Creek."

The Schoharie Reservoir, on the Schoharie-Greene counties border, is the northern most of New York City's Catskill Mountains reservoirs. The condition of the massive dam across the Schoharie Creek has long been a concern of downstream residents, even before Tropical Storm Irene in 2011, when the Schoharie Valley suffered devastating flooding. The dam held, but a sensor failure at the top of the dam contributed to public alarm.

Work on the new tunnel system began in 2017 with two segments built, both starting at a 185-foot-deep shaft along state Route 990V. A 1,188-foot segment goes downstream to the eastern bank of the Schoharie Creek, and a 930-foot segment to the reservoir bottom. Boring work was completed in January, but the drilling machine could not be removed until winter ice was gone.

 

Work still to be done in the multi-year project includes the lining of the new tunnels and installation of an intake structure. Crews are also currently working on a valve structure on the creek below the dam that will be used to control the flow of water into the creek.

 

The city is working with the state Department of Environmental Conservation on how to make water releases most effective in aiding trout and other fish.

 

The dam, which was built in the 1920s, is 2,024 feet wide and 182 feet high, and holds back up to 19.6 billion gallons of water.

 

Work on the several phases of dam upgrades began in 2005 and is expected to last until 2022.

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