Group wants Gilboa Dam siphons back in place

PHOTOGRAPHER: Patrick Dodson

The Gilboa Dam, June 2012

A local citizens group monitoring reconstruction at the Gilboa Dam is urging New York City to get siphons back up and running before winter arrives.

The New York City Department of Environmental Protection, which maintains the dam that holds back the Schoharie Reservoir for city drinking water, removed four siphons this summer. The siphons were installed during emergency work commissioned when engineers determined the dam didn’t meet current design standards. The large steel tubes decreased the water level behind the dam and therefore pressure on the dam itself.

There are plans to install two larger siphons to replace the four that were removed, but water levels following rains last month have been too high to get that installation done.

That means there’s no practical way to release water from the reservoir, Dam Concerned Citizens member Howard Bartholomew said.

The DEP is in the midst of a multimillion-dollar reconstruction project at the Gilboa Dam and the upgrades will include a low-level outlet system.

This system will enable the DEP to release water downstream into the Schoharie Creek through a gate shaft. But the design had to be revised after damage from Tropical Storm Irene.

The DEP is expecting to have the new low-level outlet completed in 2018.

The concern at this point, Bartholomew said, is the potential accumulation of snow in nearby mountains over the winter. If enough snow builds up, it could make the reservoir overflow when it melts.

Major flooding events in the Schoharie Valley historically happened during spring, not in late summer, as with tropical storms Irene and Lee last year. Record floods in history hit the valley in January 1996, April 1987, March 1980, April 2005 and April 1984.

Though siphons couldn’t do much with the massive rainfall from Irene, Bartholomew said they could help soften the blow of lesser storms.

“They can really take the top off these floods,” he said.

DEP spokesman Ted Timbers provided the following statement by email: “We are in the process of installing the new siphons — but construction cannot take place while the reservoir is spilling. Once the water level has come down we will resume installation of the new siphons. There are no dam safety issues.”