A look at the riskiest dams in the Adirondacks

Ten high hazard dams are rated ‘unsound,’ meaning their safety cannot be assured

By Zachary Matson

The owners of the Adirondack Park’s 10 riskiest dams—high hazard dams with documented deficiencies—represent an assortment of interests, resources and commitment to safety standards. Owners range from diligent lake associations to absentee developers, from towns slow to pay seven-figure repair bills to a state agency long mired in financial struggles.

While state officials in the past decade have tightened rules, hazardous dam owners are often tardy in meeting safety requirements and arranging fixes, according to an Adirondack Explorer review of dam safety records.

Many owners have failed to comply with directives to evaluate the state of their structure, and the regulators often neglect to compel action.

Half of the 50 “intermediate hazard” dams in the Adirondacks have not submitted engineering assessments despite a 2015 DEC deadline, according to inspection reports as of 2022. The assessments identify structural problems, model how dams perform against serious floods and recommend steps to align with state standards. 

Dams are classified based on the hazard they create if they fail, without regard to the likelihood of failure. “High hazard” dams pose the greatest risk and draw the most attention from regulators. Failure could result in widespread damage to homes and main roads and cause major utility disruption, substantial environmental and economic harm, and loss of human life. There are 94 high hazard dams in the 12 Adirondack counties, including 34 within the Blue Line.

Some bear a DEC condition rating, a measure of safety based on field inspections, engineering studies and regulatory compliance.

Ten high hazard dams in the Adirondacks carry an “unsound” rating, meaning safety “cannot be assured.” Another 17 intermediate hazard dams—ones that if breached could cause extensive property damage and threaten personal injury—were rated unsound, according to the DEC records. 

Deficiencies that trigger an unsound rating include water seepage, embankment stability issues and inadequate spillway capacity. During maximum precipitation rainstorms more massive than any on record in the region, unsound dams could overtop and, in some scenarios, fail outright, unleashing floodwaters on downstream communities and draining prized lakes. 

In 2009, DEC enacted regulations for high and intermediate hazard dams, requiring owners to produce engineering studies and demonstrate the structure can maintain stability and spillway function during significant storm events, earthquakes and other calamities. The rules also mandate the owners maintain and update emergency action plans for procedures to identify, prevent and respond to “adverse dam incidents.” Some owners fail to update those emergency plans annually as DEC requires.

The department’s dam safety division, with 11 engineer positions, is responsible for overseeing thousands of dams statewide. In response to Explorer questions, DEC officials said compliance is much greater for high hazard dams than intermediate hazard dams and underscored the agency’s commitment to public safety. Letters to owners after regular inspections outline where the dam falls short of requirements.

“Our staff immediately addresses any urgent conditions that are identified, remain on call every day of the year to respond to any potential concerns resulting from storms or other damaging impacts, and conduct diligent inspections of private, public, and state-regulated dams to help prevent issues before they occur,” the department said. 

Dams by the numbers

Over 500 dams dot the Adirondack Park, many built a century ago. The essential infrastructure sustains scores of beloved lakes, enables real estate value and distorts the entire landscape. Thank an old logging dam for the water-filled fjord view at Indian Head.

The average dam in New York is 86 years old, compared to the national average of 57 years, according to the American Society of Civil Engineers, and were built well before modern design standards. 

Adirondack dams have been around even longer—nearly 90 years on average. Indian Lake Stone Dam, another unsound high hazard dam, was constructed 125 years ago. An 1897 New York Times article promised “a great dam… at the headwaters of the Hudson.”

Robert Foltan, chief engineer of the Hudson River-Black River Regulating District, which owns and operates Indian Lake, Conklingville and other important Adirondack dams, said he avoids operating the gates, which took multiple years to regain function after Foltan took the position, because he doesn’t want to break them irreparably. 

Read more about Garnet Lake Dam

A group of local homeowners moonlight as dam administrators as they coordinate with the state and local government and raise money to make repairs.

Read more about the Indian Lake Stone Dam

The state agency that owns the iconic dam is moving toward an overhaul this year.

Read more about Rainbow Lake Dam

Owned by a web of companies linked to a New York City developer, state lawyers went to court to get this dam removed.

A DEC-funded flood report on the Great Chazy River published in June highlights the challenges of the North Country’s dam infrastructure, some of which has been reduced to concrete rubble and wood piles constricting stream and river channels, in both wilderness and hamlets. Old dams and their remnants can exacerbate floods and ice jams, and the report models how dam removal can relieve pressure on floodplains. 

“Deterioration is inevitable, and these dams have been in service well beyond the typical design life of even modern reinforced concrete,” the report by environmental consulting firm SLR concludes. “The state of the art was essentially in its infancy when many of these dams were built.”

Rain that never stops

When owners conduct engineering assessments, they are required to model how the dam would hold up to floods created by “probable maximum precipitation,” considered the highest amount of precipitation possible. Due to their size and age, most Adirondack dams must test against 50% of the flood produced by the probable maximum precipitation. The storms envisioned are unlike rain ever documented in the region. It would feel like the rain will never stop.

The Chazy Lake Dam engineering assessment, for example, calculated a storm of nearly 30 inches of rain over 72 hours, including a two-hour storm peak of 14 inches. The Loon Lake study projected 28 inches in 24 hours. At Garnet Lake, the maximum storm would produce 33 inches in 72 hours.

Engineers use computer models to determine if the dam has spillway capacity to absorb 50% of the flood that would be created by the massive theoretical storms. The Garnet Lake main spillway would overtop by more than five feet, according to engineers. The Loon Lake Dam would spill over for 45 consecutive hours. The assessments also evaluate a dam’s structural stability and whether it could drain its reservoir in a set amount of time. Failure to meet certain standards during tests establishes needed upgrades. 

The storms would likely represent new North Country records. The heaviest one-day precipitation in the Essex County area totaled 5.7 inches in Peru on June 16, 1987, according to the county’s emergency preparedness plan. In 1996, about seven inches of rain fell in 12 hours in Champlain. The floods that year left hundreds of miles of roads impassable and caused around $4 million in property damage. When Tropical Storm Irene swirled through the region in 2011, as much as seven inches of rain was estimated in southern Clinton County. 

The maximum precipitation amounts are pulled from Army Corp of Engineers estimates generated in the 1980s, and scientists are projecting more severe storms in the future as the climate continues to warm. A recent study by Paul Smith’s College climate scientist Curt Stager and other researchers calculated the region’s annual precipitation has increased 7.4 inches since 1900. The dramatic rain totals envisioned in the engineering models are not without precedent. Hurricane Harvey, which hovered over Houston as it turned into a tropical storm, generated 60 inches of rain in five days.

Nationwide, about 10 dams on average fail each year, according to the National Performance of Dams Program at Stanford University. In 96% of the failures, flooding did not result in loss of life or significant property damage.

Dam failure is highlighted in Adirondack county hazard preparedness plans as a low-probability risk with high downside potential. Noting that “residents and others may not be aware of dams upstream of their locations,” some of those plans recommend education and outreach campaigns to inform residents downstream and make them aware of actions to take if a failure occurred.

“Provided that adequate engineering and maintenance measures are in place, the future occurrence of dam failures in Clinton County can be considered a low probability but possible,” the county’s plan concluded.