The dam, 110 miles north of New York city, does not meet New York state's dam safety standards. It is one of the main reservoirs in the Catskills mountains that supplies New York city's drinking water supply.
The repairs are needed to protect 2500 households and businesses that are located downstream of Gilboa dam. If the dam failed it would release upto 90.9B litres of water into Schoharie creek.
The condition of the 78-year-old dam has been a concern among Schoharie county residents. New York city's Department of Environmental Protection, which controls it, has said there is no imminent danger of the dam's collapse. City officials said there was only a remote possibility of the Gilboa Dam failing, if there was a record storm and snow melt.
However, there have been scientific indications that the climate of the Northeastern US 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. A flood in April this year nearly matched that, and the area was hit with record rainfall in October. These extreme weather events led the authorities to review the dam's safety risk.
The main concern is the pressure exerted by high water levels on the dam during an extreme flood. The thrust could cause the dam to slide out of place if the bedrock beneath it is weak. And because the condition of this bedrock is not known, it has been assumed 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.
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