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March 13, 2006

Contact: Ian Michaels (718) 595-6600

City to Implement Reservoir Spill Control at Gilboa Dam

Program similar to Pepacton and Neversink to be in place after 2008 reconstruction projectWaste channel to open this week at Ashokan Reservoir

New York City Deputy Mayor Dan Doctoroff announced this morning that the City will implement a comprehensive reservoir spill control program at the Gilboa Dam after new release works are installed during the full-scale reconstruction project that will begin in 2008.  Doctoroff made the announcement at a meeting in Schoharie with Schoharie County and local officials.

Deputy Mayor Doctoroff, Department of Environmental Protection (DEP) Commissioner Emily Lloyd and others then traveled with the officials to Gilboa to review the ongoing dam stabilization project, which will bring the dam up to State standards well before the full-scale project begins. 

“Bringing reservoir spill control to the Schoharie Reservoir will help protect people and property downstream during the spring rains and thaw,” said Deputy Mayor Doctoroff.  “The full-scale reconstruction project that will start in two years will include the new valves and pipes to enable this type of relief, and New York City is committed to providing that relief to the residents downstream.  On behalf of myself and Mayor Michael Bloomberg, I would like to thank them for their patience and understanding during this difficult time.”

Commissioner Lloyd said, “This demonstrates the City’s commitment to be a good neighbor in and near the watershed.  We’ve taken every step to make the Gilboa repairs as quickly as possible, we’ve worked with local agencies to assist in their disaster response planning and we’ve reached out to residents to help keep them informed.  Future reservoir spill control is another measure to show that we care about their well-being.”

The reservoir spill control program at Gilboa will be modeled after the existing measures already in place at the Pepacton and Neversink reservoirs.  During the winter at those two reservoirs, the New York City Department of Environmental Protection (DEP) maintains voids in the reservoirs equal to one-half of the melted snow pack surrounding each reservoir.  Absent any significant snow pack, the DEP maintains the voids at a level equal to the amount of water that would runoff into each reservoir from a one-inch rainfall occurring over a six-hour period.

The reservoir spill control measures will be presented by the DEP to the State Department of Environmental Conservation (DEC) for approval.  Unlike the Pepacton and Neversink reservoirs, where any changes to the downstream water releases require the approval of all the Delaware River basin states, reservoir spill control at the Schoharie Reservoir can be implemented with just the approval of the State and the City.

Stabilization Project

Doctoroff’s visit came at a time of major progress in the work at the Gilboa Dam.  An $18.3 million contract to install 79 post-tensioned anchoring cables was awarded to  Nicholson Construction on March 8.  The 34 anchors that will be installed in parts of the dam that are thought to be potentially unstable will be completed by early August.  The other 45 anchors in more stable parts of the dam will be done by November. 

The anchoring work is the final stage of the stabilization project and will bring the dam into full compliance with DEC standards for existing dams.  Anchoring cables are being installed along the top of the dam and also on the downstream side near the spillway.  Cables are installed through holes drilled through the dam and then are anchored both to the dam and to solid bedrock below.  The cables are then tightened, creating tension that helps to hold the dam in place.

Before the anchoring work, DEP has completed installation of four large siphons to help decrease water levels in the reservoir.  The four siphons have a capacity of 125 million gallons per day (MGD) each, and extend over the dam and onto the downstream spillway.  The siphons were completed at a cost of $3.04 million.

Prior to the completion of the siphons, the DEP completed installation of a 220-foot long by 5.5-foot high notch at the western end of the dam.  The removal of the notch, at a cost of $1.15 million, effectively lowered the capacity of the reservoir, relieved pressure behind the dam and helped to secure a dry work area for the current anchoring work.

Full-Scale Reconstruction

Though the Gilboa Dam will meet State standards for existing dams at the end of the stabilization project, the $200+ million full-scale reconstruction project will increase the stability of the dam even more, allowing it to meet DEC standards for new dam construction when complete in 2011.

The project had been planned to begin in 2010 but was advanced to 2008 during the recent stabilization project.  The project will include new water release works that will enable downstream releases to the Schoharie Creek.  The project will also include rehabilitation of the intake structure for the Shandaken Tunnel, which conveys water south from the reservoir to the Esopus Creek.  From there the water enters the Ashokan Reservoir and eventually the Catskill Aqueduct.

Ashokan Reservoir Release Channel

Water levels in the Ashokan Reservoir had already been well above normal because of record rainfall in October 2005.  Flows through the Shandaken Tunnel were then increased in fall 2005 after the discovery of the stabilization problem at the Gilboa Dam.

To bring water levels down in Ashokan, the DEP will this week re-activate the Ashokan Release Channel.  The channel runs through the Ashokan Field Campus of SUNY New Paltz and eventually empties into the lower Esopus below the Ashokan’s spillway channel.  The channel will allow the DEP to make up to 600 MGD in controlled releases from the Ashokan.  DEP has leased the entire Ashokan Field Campus for this purpose through mid-June.

In another attempt to lower water levels in Ashokan, the DEP has also maximized flow through the Catskill Aqueduct since the Gilboa stabilization project began.  Flow through the aqueduct would normally be 300 – 350 MGD, but has been maintained at 580 MGD to increase diversions from Ashokan.

Increased Monitoring

A major part of the Gilboa stabilization project has involved improvements to monitoring of the dam and other areas.  Since the project began, the DEP has installed 24-hour-a-day lighting, surveillance and remote video monitoring of the dam.  There is now also automated snow monitoring of the Schoharie watershed, along with remote computer monitoring of stream gauges at the Gilboa and Prattsville.  Flow monitoring has also been installed at the Ashokan Release Channel.


More Information

NYC Department of Environmental Protection
Public Affairs

59-17 Junction Boulevard
19th Floor
Flushing, NY 11373

(718) 595-6600