Cool, clear water

Ashokan Reservior (photo by Dion Ogust)

Last bright, sunny Sunday morning I turned off Route 28 at Winchell’s Corner and drove over the dividing weir separating the two basins of the Ashokan Reservoir. In conjunction with a $15-million project completed last September to replace four massive cast-iron gates, each five feet wide, 15 feet tall and weighing nine tons, temporary traffic signals had been installed to keep only one direction of traffic crossing the weir in a single lane.

The project allows New York City’s Department of Environmental Protection (DEP) to move water between the reservoir’s west basin to its east basin in a controlled manner. By drawing the west basin down, DEP has explained, the new gates will also maximize retention time for water in that portion of the reservoir, which acts as a settling basin for sediment washed into the reservoir during heavy runoff events.

“As portions of our Catskill water supply turn a century old, this project is one of many that New York City will be undertaking to keep our system in a state of good repair,” DEP acting commissioner Vincent Sapienza is quoted as saying. “Of the 19 reservoirs in the water supply system, Ashokan was the only reservoir designed with two basins to allow for additional retention and settling time. By replacing these gates, DEP has ensured that this key infrastructure continues to operate as it was designed.”


Covering 8300 acres, the Ashokan Reservoir is twelve miles long and a mile wide. It was filled last week to 82.6 percent of its 122.9 billion gallons of capacity. When full, the Ashokan alone without further precipitation could satisfy New York City’s water needs for over four months.

I noted a small island in the west basin that isn’t there when the reservoir is full. There was empty shoreline whose vegetation indicated that it was considerably below capacity. I reminded myself the Ashokan had an average depth of 140 feet; what I was seeing was a very small proportion of what lay below the surface, analogous to the situation with an iceberg.

I drove eastward on Route 28A to the famous spillway that when overflowing would release a torrent of water into the Esopus Creek, often enough to cause damage to downstream flood-prone areas of Marbletown, Hurley, Ulster and Saugerties. The east basin seemed benign in the bright sunlight, its settled waters several feet below the top of the concrete wall of the spillway. It was hard to think of such a huge surface area filling in a couple of months with water; by my calculation, a stupendous 21.5 billion gallons of additional water would be needed to fill the Ashokan.

Then I remembered something I had read in a caption in the most recent DEP Weekly Pipeline: “The melting snow from these mountains, paired with spring rains, accounts for an average of 400 billion gallons of runoff into New York City’s reservoir system each year.” With that larger figure in mind, the 21.5 billion gallons shortfall of water in the Ashokan is equivalent to the proverbial drop in the bucket. At 79.4 percent of capacity as of February 16, the DEP reservoirs are 114 billion gallons below capacity. The odds that the runoff will fill them seem to me pretty high.

The risk of a drought has diminished substantially in the past two and a half months, though a statewide water watch is still in place. The gap between “current” and “normal” conditions has steadily narrowed. At the beginning of December, existing New York City reservoir water was at 56.9 percent of capacity as compared to a normal 81.4 percent. By the end of December, existing proportion of capacity had increased to 64.8 percent as compared to a normal of 87.2 percent. By the end of January it had climbed to 76.9 percent as compared to 88.7. On February 16 it was 79.4 percent compared to 88.2 percent. Even prior to the expected snow melt, which this year seems already to have started (that’ll have to be factored in), the differential between the two has changed from 24.5 percent of system capacity to 8.8 percent as of last Friday.

Most importantly, this dramatic improvement has taken place without a big nudge from increased precipitation. The amount of rain and snow this winter has been at the historical average. The system has replenished itself, compensating rapidly with normal precipitation for the shortfall caused by the drought.

The seven major reservoirs in the New York City system (Schoharie, Cannonsville, Neversink, Pepacton, Ashokan, Rondout and Croton) have 552.5 billion gallons of capacity. New York City consumes a billion gallons a day, and the upstate communities connected to the system another 100 million. Even with a larger New York City population, city water consumption has been reduced from a billion and a half gallons a day at the time of the last major drought 28 years ago to a billion gallons a day.

Maybe it’s already time to be talking not about too little water but too much — the more common condition in the New York City reservoir system in springtime.

Ulster town supervisor James Quigley keeps daily track of the amount of water in the New York City reservoirs. When does he start to worry about Ashokan water flooding over the spillway to cause problems for the low-lying areas of his town? He says he starts to pay close attention when the Ashokan reaches 90 percent of capacity. Two of his colleagues, Michael Warren of Marbletown and Gary Bellows of Hurley, think the downstream municipalities need to be involved at 80 percent of capacity, reports Quigley.

As part of its mission, DEP spends billions of dollars on water supply projects both large and small. It’s spending $600 million on a new tunnel to transport its Rondout system water under the Hudson River. It’s contributing $12 million for New Windsor to connect to the Newburgh water system rather than to DEP’s. It’s fixing leaks in its distribution system in New York City, installing universal metering for its water users, and eventually completing its fabled third water tunnel — a still-incomplete project now a century in the planning and construction.

The upshot of all this activity is that the amount of water DEP needs to produce to meet demand continues slowly to decrease. From the agency’s point of view, that’s a good thing, particularly in an era of increasing climate uncertainty. The likelihood of insufficient supply — a catastrophic occurrence — has been diminishing.

Six years ago, DEP and the state Department of Environmental Conservation announced a first-ever agreement in regard to use for overflow of the release channel from the Ashokan to the Esopus Creek below the reservoir. These limited releases, then-DEC commissioner Joe Martens said, “were appropriate at this time to limit flooding in communities along the Lower Esopus Creek and reduce turbidity in water flowing toward the New York City drinking-water system.” Daily releases of up to 600 million gallons of water were involved.

DEP’s use of the Ashokan release channel to dump turbid water into the Esopus is a new area of concentration under the 2017 proposed FAD. With the renewal process of the agency’s all-important filtration avoidance determination for the next ten years from the federal and state governments coming up this year, DEP is adjusting its focus.

DEP’s assessments are based on improving the integration of data from its monitoring, modeling and GIS programs. At the same time, the agency keeps updating the preliminary designs of a massive filtration plant whose construction it hopes to postpone for as long as possible.

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