UPPER DELAWARE RIVER, NY & PA — Record-breaking levels of drought throughout the Delaware River watershed have sent ripples through the entire river valley. 

This week, New York City (NYC) declared a drought warning, and called a pause on a long-awaited project to repair the Delaware Aqueduct. This aqueduct carries water from the Delaware River to NYC, and had been closed starting on October 1 for repairs. 

The aqueduct will reopen to allow drinking water from the Delaware River to reach the city again. That decision will mean there's less water in the reservoirs along the Delaware River, which could affect drinking water supplies as far south as Philadelphia and tip the Delaware River basin into a drought declaration of its own. 

Re-opening the aqueduct: Why was it closed?

The drought warning declaration means the city will postpone its project to repair the Delaware Aqueduct for the third year in a row. 

When in operation, the Delaware Aqueduct carries 600 million gallons of water per day from the Delaware River to NYC, supplying the city with half its daily supply of drinking water. That aqueduct needs to be closed for a five-to-eight-month period so that that the NYC Department of Environmental Protection (DEP) can repair a set of leaks near Newburg and Wawarsing. The leaks were discovered in the 1990s, and they release around 35 million gallons of water per day from the aqueduct, according to NYC. 

The DEP has prepared for decades to ensure that NYC will have enough water to sustain itself during the shutdown, spending hundreds of millions of dollars increasing the city's other water sources and reducing the city's water needs. It postponed that shutdown twice, in 2022 and 2023, to make sure that everything was ready and in place. 

This year, the shutdown went ahead as planned on October 1. However, the weather had other plans. 

"As our city and watershed continues to experience significant precipitation shortages, I'm upgrading our drought watch to a drought warning, pausing our Delaware Aqueduct repair project, and ordering our agencies to immediately implement water saving measures," said NYC Mayor Eric Adams, speaking on November 18. 

According to a press release from the city, the project will restart next year. 

Upstream effects of re-opening

As the Delaware Aqueduct re-opens, and resumes withdrawing hundreds of millions of gallons of water per day from the Delaware River, the rest of the watershed will feel the effects. 

Hundreds of billions of gallons of water are stored in reservoirs along the Delaware River. Right now, there's much less water in these reservoirs than normal, according to Amy Shallcross, manager of water resource operations with the Delaware River Basin Commission (DRBC). 

This chart, shared by the Delaware River Basin Commission during a November 19 public hearing, shows this year's level of storage in the New York …

Speaking at a public hearing held November 19, Shallcross said the reserves that feed the NYC water supply system are already at lower than normal capacity (52 percent) due to larger than normal releases of water into the Delaware River to maintain flow levels at Montague, NJ.

The DRBC is tasked with maintaining a set rate of flow (the speed at which the river travels out to the sea) at specific points along the Delaware River. These rates were established to make sure the freshwater Delaware River pushes against the saltwater from the ocean and keeps it from infiltrating Philadelphia's water supply. If there's not enough water in the river to keep up that rate of flow — say, from a lack of rain — the DRBC needs to release more water from its reservoirs upstream, putting more water into the river. 

The DRBC has been making releases from its reservoirs since August to meet requests for flow downstream, said Shallcross. Even with these additional releases, as of November 18, the salt front — the point where freshwater and saltwater meet — is 19 miles upriver from its normal location in November and only 13 miles downstream from its location during 1960's drought of record. 

As the Delaware Aqueduct reopens, due to NYC's drought warning, the city will resume diverting water from the Delaware River to meet its needs, further emptying reservoirs that are already lower than normal. As those reservoirs drop, the DRBC could end up on drought footing itself. 

Currently, the NYC reservoirs have 29 billion gallons of water stored above the level that would trigger a drought watch, said Shallcross. If that changes, or if other indicators lead the DRBC to start drought operations, it would further restrict releases and water diversions from its reservoirs, to ensure that it kept enough water in reserve to keep saltwater out of Philadelphia's water supply. 

Rain, rain dependent

Whether that will happen largely depends on the weather. 

"The lack of rain is the foundation of everything here," Jeff Skelding, executive director of the non-profit the Friends of the Upper Delaware River, told the River Reporter. 

Skelding said in the absence of rain, reservoirs will get even lower, with releases potentially being affected through the fall and winter. 

Shallcross said the forecast looks good for rain this week — 1.5 inches in the upper Delaware River area, with less further downstream. However, other forecasts of rain have not panned out, she said. 

As of Wednesday morning, November 20, that forecast is changing to snow for much of the Upper Delaware. Sullivan County has been put under a winter weather advisory, according to Sullivan's 911 center; "the bulk of Sullivan is forecast to receive only a trace to an inch of snow, but our northern and higher reaches could see 4-7 inches accumulate" between Thursday night and Saturday morning, reads a Facebook post from the center. 

Even if some precipitation does fall, that might not make up for the current shortage. 

The past 90 days have been "dismal" for rain, with most major gauges measuring the driest on record, said Shallcross. She said the upper Delaware River basin received around four inches over the past 90 days, around a third of what is normal, and that the lower basin has received far less. 

In a statement given to local media, Upper Delaware Council Executive Director Laurie Ramie said, "“It’s very unfortunate that this dry spell conspired against completing these Delaware Aqueduct repairs that have been planned for 20 years and finally initiated after two prior postponements. All the best modeling, forecasting, and engineering can’t prevail over Mother Nature ultimately. We don’t know yet the full consequences of this delay, but since the New York City Department of Environmental Protection has been very transparent in updating the Upper Delaware Council throughout this long process, we fully expect to receive more information.”

Skelding said the details are still getting sorted out about the closure of the Delaware Aqueduct, but that he's concerned about the impact on the reservoirs and the river. 

"Once they make the call to halt this project, that's it, there's no going back," said Skelding. He said with this being the third postponement in as many years, most people just want to see the project done and behind them. 

The River Reporter sent a set of questions to the NYC DEP and will update this article with the DEP's responses once received.