Above: A Flickr slideshow of photos taken during a DEP-led tour of the Gilboa Dam for local officials and media. Photos by Lissa Harris.
Cross your fingers for good weather in Gilboa this summer.
Weather permitting, a $400 million reconstruction project at the Gilboa Dam is on track to be finished almost two years ahead of schedule, according to officials at the New York City Department of Environmental Protection. The project, begun in 2011 and originally slated for a 2016 completion date, is now likely to be finished in 2014.
Decades of wear have taken their toll on the 87-year-old dam, and constant freezing and thawing have eroded the dam's massive stone face. In 2005 and 2006, the DEP undertook some emergency stabilization work to strengthen the dam. The current -- and far more ambitious -- reconstruction project now underway at the dam adds dozens of post-tensioning anchors, several hundred million pounds of concrete, and a reconstructed spillway.
On Tuesday, local officials and news reporters donned hard hats and safety vests to get a tour of the construction site, on the northern end of the Schoharie Reservoir.
Among those gathered to see the DEP's progress was Assemblyman Pete Lopez, whose hometown of Schoharie was ravaged by Irene flooding in 2011. For Schoharie and other towns downstream of the Gilboa Dam, the 17.6-billion-gallon reservoir that looms over the valley is a constant worry, Lopez said.
"The dam is a physical presence in their lives," he said.
Since the installation of two new temporary siphons over the winter, people in downstream towns have been breathing a little easier. The siphons, each six feet in diameter, were installed to give the DEP the ability to draw down water levels in the reservoir ahead of time if flooding is predicted. The two siphons replaced four smaller (and even more temporary) ones that were removed last summer, leaving the DEP with no way to drain water into the Schoharie Creek for months.
In the long term, the siphons will be replaced by a permanent low-level outlet that will shunt water from the reservoir into the Schoharie Creek. The outlet is scheduled to go into operation in 2019, several years after the dam reinforcement is completed.
Another project -- the rehabilitation of the Shandaken Tunnel, an 18-mile underground aqueduct that carries water from the Schoharie Reservoir into the Esopus Creek -- will be finished in 2018.
All told, the DEP's work on the Schoharie Reservoir infrastructure will not be finished until around 2022, when the site restoration is scheduled to be finished.
During Tuesday's tour, one of the siphons was gushing water at a rate of 250 million gallons a day, with a deafening roar that threatened to drown out the sound of DEP regional manager Carl Davis's bullhorn, as Davis pointed out features of the ongoing construction.
Being able to lower the reservoir in advance of possible flooding is especially important in the spring, when increased rainfall and melting snow tend to raise the risk of flooding in the region. DEP deputy commissioner Paul Rush said on Tuesday -- a chilly day in an unseasonably cold April -- that there was still about 0.8 inches of snowpack on the ground, an amount that translates into about 4 billion gallons of water in the Schoharie Reservoir's watershed.
Keeping track of how snowmelt, rainfall and other environmental conditions affect water bodies downstream is a complex science. The DEP is in the process of adopting a new computer water-data-tracking system, dubbed the Operations Support Tool, that DEP officials say will soon begin yielding better forecasts of flooding, streamflow and reservoir levels.
Although the Gilboa Dam reconstruction began before Irene, some lessons learned in the flood have been incorporated into the project. During the Irene floods, the DEP lost communication with the Gilboa Dam's extensometers, instruments that monitor stress on the dam.
DEP construction manager Emory Chase said that new extensometers have been relocated to a more secure location in the dam.
But the biggest lesson to come out of the Irene floods, said Rush, was the importance of acting conservatively in the interest of public safety when quick decisions must be made.
As an example, Rush pointed to the agency's decision to declare a Type B emergency at the dam after they lost contact with their sensors -- a declaration meaning that the dam may be in danger of failing, and the evacuation sirens must be sounded downstream.
Even though the dam did not fail, the decision was the right one, Rush said.
"The sirens saved lives," he said.
Gilboa Dam project by the numbers:
234,000,000: Pounds of concrete that will be used to reinforce the dam, by the time the project is completed.
500,000,000: Gallons per day that the two temporary siphons currently in place can release from the Schoharie Reservoir into the Schoharie Creek.
1,500,000,000: Gallons per day that a permanent release tunnel will be capable of releasing from the reservoir, when it is completed in 2019.
110,000: Cubic feet of water per second that spilled from the Schoharie Reservoir during the highest point of Irene flooding -- a rate that translates to 71,090,000,000 gallons per day.
877,000: Cubic feet of water per second that would spill into the Schoharie Valley if the Gilboa Dam failed.
125: Local jobs that the Gilboa Dam restoration project has created.
More local media reports:
A radio report from the tour, by WAMC's Dave Lucas.
A video report, by YNN's Maria Valvanis.
Below: A Flickr slideshow of photos of the tour and of ongoing construction work at the dam. Photos by NYC DEP.
