Dam at a Catskill Reservoir Needs Emergency
Repair, City Says
The New York Times, Nov. 28, 2005
FULTONHAM, N.Y., Nov. 23 - A massive 78-year-old dam in the Catskill Mountains that is owned by New York City does not meet state safety standards and will have to undergo emergency repairs before next spring's snow melt.
City officials said there was a remote possibility that the Gilboa Dam would fail if there was a record storm and snow melt, sending the 20 billion gallons of water in the Schoharie Reservoir roaring through the valley below, a historic area of covered bridges and small farms that is home to about 5,000 people.
In an attempt to reduce the danger as quickly as possible, the city has been trying to lower the reservoir level in recent weeks by sending as much as 540 million gallons of water a day through a 17-mile tunnel. The water flows into a more southerly reservoir, the Ashokan, where it must be treated with aluminum sulfates to remove sediments before it is released to New York City.
But the Schoharie Reservoir refills with rain as fast as the water drains out. The city is now considering hanging 10 large drainage hoses, 24 inches in diameter, over the top of the dam to siphon out more water.
The New York City Department of Environmental Protection, which owns the 1,800-foot-long dam, has held several meetings with frightened local residents, trying to explain the risk without provoking panic.
"We don't expect to have a failure of the dam," Emily Lloyd, commissioner of the department, calmly told about 150 local residents who packed into the pine-paneled community room of the United Methodist Church here during a light snowstorm last Tuesday night. "We do have some concerns that we want to share with you."
In the wake of the breakdown of civil order in New Orleans after Hurricane Katrina, Ms. Lloyd said she felt it was necessary to inform residents of the danger and to help them prepare an evacuation plan, though the chance that the dam will fail is remote.
City officials said the emergency was based on a question of safety that is caused by a shift in weather patterns, not a sudden deterioration of the dam. There have been scientific indications that the climate of the Northeast is changing and that storms that were once rare are now far more common.
The Schoharie Valley was hit with 100-year-floods in 1955, 1987 and again in 1996, when the Schoharie Reservoir reached its all-time high water level, more than six and a half feet over the top of the dam. A flood in April nearly matched that, and the area was hit with record rainfall in October.
"Seems like we've got 100-year floods coming every nine years now," said Fred Risse, a local farmer whose land lies in the flood plain of the Schoharie Creek. "What happens when we get another?"
Extreme weather led the department to recalculate the dam's safety risk. And because it does not know the condition of the bedrock below the 183-foot high dam, it has had to assume that it is in the worst condition possible.
That uncertainty, combined with accelerated deterioration of the dam's stone facing in the last 25 years, and some other possible defects discovered in recent inspections, have increased the likelihood that the dam could fail under extreme conditions.
Commissioner Lloyd said the dam was still safe under normal conditions. But in the event of the worst possible storm - a 1-in-10,000-year flood - the dam would have no reserve strength and therefore no longer meets state safety standards.
Such a storm would have to be monstrous, with 25 inches of rain in 72 hours. It would push the water in the reservoir eight feet above the dam, two feet higher than the record level in 1996.
"If there were a series of terrible storms, we might, over a few days, have to get the people's attention, and we don't want to do that on short notice," Ms. Lloyd said in an interview after last Tuesday's meeting. "We want to err on the side of being prepared, and we can't do that without reaching out to people this way."
While declaring an emergency gets people's attention, it can also cause panic if people fear that a collapse is imminent. Local newspapers have been filled with breathless stories about floods, failures and evacuations since the commissioner first met with local officials in late October.
Residents of this rustic and historic valley, 110 miles north of New York City, have grown increasingly uneasy. No strangers to floods, they have demanded to know how much time they would have to evacuate, where they are supposed to go, and who would notify them. Some have moved valuables to higher ground, and they worry about sending their children to school.
"They've got everybody hitting the panic button," said Imer Barton of Schoharie, who concedes that he sees things differently because he lives on a hill, out of danger. "It's good to be knowledgeable, but this is not a new problem."
The Gilboa Dam was completed in 1927. It was built in two sections, a stepped concrete dam more than 1,000 feet long that abuts an earthen berm on Schoharie Creek. It is the northernmost of the city's 22 dams and was identified several years ago as most in need of repair.
Howard R. Bartholomew, a retired history teacher and cabinetmaker who has lived downstream of the dam his entire life, said he had watched it steadily deteriorate.
"This was a marvel of engineering," said Mr. Bartholomew, 62, as he stood on an embankment overlooking the dam. He pointed out that many of the three-foot thick bluestone blocks on the downstream side of the dam had been washed away. Steel reinforcing bars are exposed, and the enormous concrete apron on the spillway below the dam is pockmarked with holes.
"There's only one word for this," he said. "Appalling."
At Tuesday night's meeting, residents asked how the city could have ignored the dam for so long. Gail S. Schaffer, a former New York State secretary of state who lives in Blenheim, close to the dam, said the years of deferred maintenance "bordered on negligence."
The Schoharie Reservoir provides about 16 percent of New York's drinking water and cannot be shut down while repairs take place.
Rather, the city plans to drop the reservoir level by up to 16 feet, relieving pressure on the structure. Early next year, engineers will cut a notch 200 feet long in the top of the dam's westernmost section to keep the water level low.
The dam is still sturdy enough, engineers said. It is 150 feet wide at its base and composed primarily of high-strength concrete. Rodney E. Holderbaum, a consulting engineer hired by the city for this project, said the concrete was in comparatively good shape beneath the missing bluestone blocks. The main concern is not erosion. Rather, excess water pressure from a monster flood could cause the dam to slide out of place if the bedrock beneath it is weak.
In determining the dam's margin of safety, engineers had to assume that the bedrock was badly deteriorated. But Paul Rush, director of West of Hudson Operations for the Department of Environmental Protection, said the bedrock was unlikely to be in such poor condition.
The commissioner's decision to issue an emergency advisory allows the city to undertake $18 million in repairs without going through the normal bidding process, which can take months.
The city plans to drill up to 90 holes in the dam, some straight down from the top into the bedrock, and others diagonally at the toe of the dam. Anchors will then be cemented into the bottom of those shafts, and posts and cables will be run up to the surface so they can be tightened.
Lawrence Sweeney of Watsonville, who lost his house in the 1996 flood, said he doubted that the repair would work. "Soon as you start putting holes in there, it's like using an ice pick on a block of ice," he said. "It's going to break."
Mr. Rush said that this kind of repair had been used successfully on 1,000 dams around the world.
Once the reinforcements are complete, he said, the Gilboa Dam should again meet state safety standards.
The dam is scheduled to undergo a complete $200 million reconstruction beginning in 2010.