Downstream residents express concerns over Ashokan Reservoir discharges

A section of the lower Esopus Creek.

Adam Bosch

Residents of the towns downstream from the Ashokan Reservoir voiced their complaints November 18 at the Frank D. Greco Senior Center in Saugerties to New York City Department of Environmental Protection (DEP) officials about the brown water that has fouled the Esopus Creek over the past few years, and of flooding that they thought the reservoir’s dam was supposed to prevent.

Two representatives of the DEP tried to explain what the City could do and what it could not do. Changes in weather patterns, constraints on chemicals used to make silt and contaminants sink to the bottom of the reservoir have made control of the muddy discharges more difficult.

Adam Bosch, the DEP Public Affairs Director, said the supervisors and mayors of municipalities affected by the New York water system wanted to know about how the department works, how water quality is maintained — or for downstream communities sometimes not maintained — and what a planned shutdown of the reservoir releases will mean to the downstream communities.


The New York water system is partly served by a 93-mile aqueduct that carries water from the Ashokan Reservoir to the northern border of the city. The full system is comprised of 15 reservoirs and three lakes. When all the parts of the system are full, it holds about 573 billion gallons of water, Bosch said. It serves 9.8 million people, or about half the population of New York State. New York’s water supply is the largest in the country, and 90 percent of the water is unfiltered. The system collects water from a drainage area of 972 square miles. The system is unique in that water is transmitted by gravity alone, Bosch said. He asserted that buildings in the oldest parts of the city were mainly five or six stories tall because that was the limit gravity alone could push water up.

The New York water system is actually three systems. The Croton water system, started in 1842 is the oldest. The Catskill system, which includes the Ashokan reservoir was built between 1907 and 1927, Bosch said. The last system to be built was the Delaware Reservoir system, which is also the westernmost system.

The developers of New York’s water supply were aware that turbidity built up after heavy rains, and they tried to find ways around it, Bosch said. Treatment with aluminum sulfate, or alum, which bonded to the silt and caused it to sink, was an early weapon in the fight against turbidity. The Ashokan reservoir was built with two basins to control the turbidity — one to allow the turbidity to settle, and the other to supply the clean water to the city. 

Water leaves the reservoir in three ways: through the aqueduct to the city, over the spillway when the water coming in exceeds its capacity and is spilled into the Esopus Creek, and finally through the release channel, which allows the city to release water to the Esopus via the Beaverkill. 

The basins are separated by a weir, which separates the two basins. Silt builds up in the west basin, where it will gradually settle; the clean water is transferred to the east basin,

“The system works well most of the time, but the “challenge occurs every ten years, when the turbidity builds up.” Turbidity is affected by human activity — controlling streams natural spread, adding reservoirs and preventing water from spreading out.

The system has been under stress the past few years, with record rainstorms, heavy snow and ice melt, all of which have increased the flow of silty water to the creek, Bosch said. The water delivered to the Kensico Reservoir in Westchester must meet specified turbidity levels. 

But, Bosch said, people should realize the Esopus watershed has its own sources of turbidity. The streams that feed the Esopus, such as the Sawkill and the Plattekill, pick up mud and silt after a storm and carry it to the Esopus. “Water from the reservoir actually spreads this turbidity, reducing it but spreading it out over a longer time.”

In its first 80 years, the Ashokan Reservoir did not require releases of turbid water; the turbidity was controlled with alum when it got really bad. But in 1989, the environmental organization Riverkeeper sued the city on the grounds that the addition of some chemicals was illegal. While the suit was eventually dropped, the city, concerned about the possibility of future lawsuits, dropped the use of alum, except in severe cases.

Following the decision to stop using alum, the city conducted a major study to find another way to reduce turbidity. No effective means was found, Bosch said. Some changes, such as drawing water from the west basin when the water is clear so it has capacity for turbid water when necessary, better filtration and other methods have helped, Bosch said, but they cannot fully solve the problem.

In response to a question, Bosch said a filtration plant for the water system would cost more than $10 billion, and would cost $250 million a year to operate.

Responding to another question, Bosch acknowledged that when the reservoir is over full, there’s a conflict between sending muddy water down the Esopus Creek from the west side or clean water from the east and curtailing the clean water supply to downstream New York City residents, and it can be difficult to balance the competing interests. “Nobody, including us, is going to get what they want all the time.”

Saugerties resident and historian Vernon Benjamin asked why, when the Ashokan Reservoir was close to full, the DEP did not favor the Ashokan for supplying water to New York, drawing it down. “We tried that, but this year we got more water than we could send,” Bosch said. “There’s a limit to the amount of water we can send out, but there is no limit to the amount of water nature can send in.” New York City/s reservoirs were built as water supply reservoirs, not flood control reservoirs, he said, and the object is to keep them nearly full so there is water available when the next drought hits.

Paul Malmorez asked whether the past year’s flooding might indicate that the DEP’s algorithms are out of date and not working. “In September you were above 90 percent, and now you’re above this. Now you have the aqueduct shut down, so if you have a major storm, like we’re supposed to have at Thanksgiving, it will be flooding the people on the lower Esopus, and I’m wondering what you’ll be doing to mitigate those situations.”

“First, we’re not flooding anybody,” John Vickers, P.E.. Chief, Western Operations Division Directorate said. “The presence of the reservoir even when it’s full, mitigates the flow.” He acknowledged that it could be possible to improve the flow, but there are decisions that have to be made — how much risk to the water supply versus how much void can be provided,”


One woman, a New York City and Ulster County resident, said she loves her New York water. “I’m thinking of bottling it and bringing it up here.” But, she said, that water should not come at the expense of muddy water in Ulster County. She also alluded to recent news reports of high levels of possible cancer-causing chemicals in water in Ulster County.

Bosch said he agreed she should have clean drinking water, but the New York City reservoirs don’t supply drinking water to Ulster County, or take its water away. 

Following the meeting, Saugerties Supervisor Fred Costello said the meeting was informative, and he had learned some new information about the New York system. The meeting’s purpose was more informative, an exchange of ideas, rather than actions.

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