Dam safety: A doomsday scenario

By LINDA DROLLINGER
Posted 3/10/21

NARROWSBURG, NY — How do you prepare for a disaster of epic proportions? Director of Public Affairs for New York City Department of Environmental Protection (DEP) Adam Bosch answered that …

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Dam safety: A doomsday scenario

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NARROWSBURG, NY — How do you prepare for a disaster of epic proportions? Director of Public Affairs for New York City Department of Environmental Protection (DEP) Adam Bosch answered that question in his March 4 presentation to the Upper Delaware Council (UDC).

The presentation, “Update on New York City Dam Safety Notifications,” focused on DEP’s capability to deliver timely notification of dam failure to unsuspecting souls downstream. A complete rupture of the Cannonsville Dam could result in spillage of up to 95.7 billion gallons of water.

“That assumes a 600-foot wide stretch of dam disappearing at once,” said Bosch. “From watching videos of other dam failures, we know dams don’t fail that way. But, for sudden failure analysis, we’re obliged to consider a worst-case scenario; this is it.”

Although the New York City water supply system comprises 19 reservoirs and three lakes, it is the Cannonsville Reservoir dam, the largest and newest in the system, that would pose the greatest threat to the Upper Delaware region if it failed. Located in Delaware County near the Village of Deposit, the Cannonsville Dam impounds over half of the West Branch of the Delaware River and draws its name from the former Town of Cannonsville, which was demolished to make way for the reservoir.

In use since 1964, it is the most instrumented dam in the NYC water supply system. “That’s because engineers in the 1960s had more instruments at their disposal than their predecessors did,” said Bosch. Numerous piezometers, instruments used to measure water pressure, produce readings monitored by a team of safety experts.

“Our dam safety program is among the best in the world. We know this because it serves as a model for dam safety best practices employed by other large dams around the world,” notes Bosch. He explained that dams are assigned hazard ratings, based on both the size of the dam and the size of the downstream communities its failure would jeopardize. Bosch states, “DEP’s number one priority is the safety of people downstream of the dam.”

To safeguard those downstream communities, the DEP routinely performs tabletop exercises designed to measure and decrease the time it takes to detect imminent dam failure and notify downstream communities of the need to evacuate. The evacuation itself would then be undertaken by emergency services personnel. Until recently, however, it took longer to notify the downstream communities of an impending disaster than it would take the water to reach them in the event of dam failure.

If the Cannonsville Dam experiences sudden failure, the water it contains will reach the first downstream community in 26 minutes. How quickly DEP detects imminent dam failure and sends an alert to those downstream will determine the survivability rate.

In the 19th century, ringing church steeple bells was the rural emergency alert system of choice because churches were ubiquitous and at the heart of community life. In the 20th century, sirens were the rural emergency alert system of choice because volunteer fire departments were ubiquitous and at the heart of community life. But in the 21st century, cell phones are the emergency alert notification of choice because they are in the hands of almost every person over the age of eight. To that end, DEP has purchased software capable of sending emergency alerts instantly and simultaneously to citizenry and emergency services personnel alike.

After noting that the Delaware River corridor is famous for spotty cell service, Bosch said the next initiative of DEP will be to convince local government officials to build new cell towers and upgrade those already in existence.

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