Dam Information

NYS DEC Dam Safety Website
NYS DEC Dam Safety Website 

New York State uses a dam downstream hazard classification system similar to that of many states and federal agencies. The following three classification levels are used in New York. They are listed in order of increasingly adverse consequences from a dam failure. These classification levels build on each other, with the higher levels adding to the consequences of the lower levels. These downstream hazard classifications are defined in 6 NYCRR Subpart 673.5(b), and are repeated here for reference.

# in Schoharie County
Class A
Low Hazard
(1) Class “A” or “Low Hazard” dam: A dam failure is unlikely to result in damage to anything more than isolated or unoccupied buildings, undeveloped lands, minor roads such as town or county roads; is unlikely to result in the interruption of important utilities, including water supply, sewage treatment, fuel, power, cable or telephone infrastructure; and/or is otherwise unlikely to pose the threat of personal injury, substantial economic loss or substantial environmental damage. 49
Class B
Intermediate Hazard
(2) Class “B” or “Intermediate Hazard” dam: A dam failure may result in damage to isolated homes, main highways, and minor railroads; may result in the interruption of important utilities, including water supply, sewage treatment, fuel, power, cable or telephone infrastructure; and/or is otherwise likely to pose the threat of personal injury and/or substantial economic loss or substantial environmental damage. Loss of human life is not expected. 19
Class C
High Hazard
(3) Class “C” or “High Hazard” dam: A dam failure may result in widespread or serious damage to home(s); damage to main highways, industrial or commercial buildings, railroads, and/or important utilities, including water supply, sewage treatment, fuel, power, cable or telephone infrastructure; or substantial environmental damage; such that the loss of human life or widespread substantial economic loss is likely. 7
A fourth classification is provide d in 6 NYCRR Subpart 673.5(b) to track the files of structures that were never built or are no longer dams:
Class D
No Hazard
(4) Class “D” or “Negligible or No Hazard” dam: A dam that has been breached or removed, or has failed or otherwise no longer materially impounds waters, or a dam that was planned but never constructed. Class “D” dams are considered to be defunct dams posing negligible or no hazard. The department may retain pertinent records regarding such dams. 4

Dams provide many functions for a community, including recreation, flood control, irrigation, water supply and hydroelectric power. Dams range from massive concrete structures to smaller earthen structures, such as those near a farm’s pond.

But dams also can increase the risk for floding. Intense storms can raise water levels and produce a flood within a few hours or even minutes. Dam failure may occur within hours of the first signs of breaching or overtopping. Other factors, such as debris jams or an accumulation of melting snow, can cause breaches days or weeks after the first sign of trouble. Flooding can occur downsteram when excess water is released in an effort to avoid overtopping or a breach at the dam.

Gilboa Dam (Schoharie Reservoir)

Gilboa Dam

Owned by NYC DEP, the Schoharie Reservoir was created by impounding Schoharie Creek. Portions of it lie in the towns of Conesville and Gilboa in Schoharie County, Roxbury in Delaware County, and Prattsville in Greene County.

Constructed in 1919-1927 and placed into operation in 1927, the Dam has been in service for almost 90 years. The average storage capacity of 17.6 billion gallons provides approximately 16 percent of the total water supply for NYC. Water travels through the Shandaken Tunnel about 15 miles to the Esopus Creek.

Gilboa Dam

Gilboa Dam is a classic NYCDEP gravity dam design, consisting of a 160 foot high by 1,326 foot long spillway, constructed of mass cyclopean concrete with a 3-5 foot thick Ashlar masonry facade of mortared quarried stone on the entire downstream face. The Dam is abutted on the west by a 160 foot high by 700 foot long Earthfill embankment section consisting of homogenous rolled earthfill with a concrete corewall. A stair-stepped overflow structure, also constructed of cyclopean concrete with stone veneer facing, cascades water from the spillway into the side channel. The stepped spillway is intended to dissipate energy as water overflows the spillway.
In December 2005, remedial measures began to ensure that the Gilboa Dam satisfied NYSDEC dam safety criteria for the stability fo the gravity section. The primary emergency structural improvement to the dam was installation of post-tensioned anchors in the spillway and its foundation.

There are no flood control devices on the structure, so once the reservoir exceeds 1,130 feet elevation, water will flow over the spillway into the side channel.

NYPA Dam (Blenheim-Gilboa Reservoir)


Owned by the NY Power Authority, the Blenheim-Gilboa Pumped Storage Power Project generates more than one million kilowatts of electricity in peak demand periods by drawing water from the Schoharie Creek and recycling it between two huge reservoirs.

Nestled beneath 2,000 foot tall Brown Mountain, B-G serves two vital functions. It saves money for NY consumers by providing low cost electricity when they need it the most, and it stores water for emergency power production. If needed, the project can be up and running within two minutes and can take over if another plant or line suddenly goes out of service.

NYPA DamEach of the reservoirs – one atop Brown Mountain, the other at its foot – holds five billion gallons of water. When generating power, the water cascades down a concrete shaft that’s five times taller than Niagara Falls. When storing water, usually at night or over the weekend, the process is reversed and water is pumped back up the shaft for storage.

The B-G Project is regulated by the Federal Energy Regulatory Commission (FERC), and are required to release the same amount of water that comes into the reservoir. For example, if 1,000 cfs of water flows into the reservoir, NYPA is required to allow 1,000 cfs of water to flow out of the tainter gates into the spillway. However, in emergency situations, with FERC permission, NYPA is allowed to “step” the release to protect downstream. This means that if they can safely hold some water temporarily until stream levels go down, they will do so.  This is not always possible – the safety of the dam/power station must be taken into consideration.


The NYS DEC Dam Safety Division’s “Owners Guidance Manual for the Inspection and Maintenance of Dams in NYS” is available for download below.

New York State DEC Dam Safety has developed the following six informational documents for dam owners (see below):

    • Dam Inspections by Owners
      How to perform periodic maintenance and inspections. Includes the basic components of a dam, what to look for during an inspection, and potential problem indicators.
    • Low Level Dams
      Information on the operation, maintenance and problems of low level drains.


The following are links to the NYS DEC Dam Safety Forms