Ocean salt water entering Delaware River due to drought and sea level rise, water managers say

Drought and sea level rise have caused salt water from the Atlantic Ocean to creep into the Delaware River Basin, a major source of drinking water for Philadelphia and the surrounding area, officials say.

The Delaware River's salt front -- the line where ocean water and freshwater meet -- has been shifting upstream from its typical spot near Wilmington to about 20 miles north, near the Philadelphia International Airport and closer to the intake for drinking water, Amy Shallcross, manager of water resource operations at the Delaware River Basin Commission, said.

"When flows are really low, that's when the salt front will start to creep upstream," Shallcross said.

Drinking water has not yet been affected, but water management officials are taking urgent measures to prevent the ocean water from tainting the water supply, Shallcross said.

One of the contingency efforts includes tapping two nearby reservoirs to push the unpotable waters back downstream, Shallcross said. The flows released are roughly equivalent to two Olympic-sized swimming pools per minute.

"As conditions become more and more serious, or drier and drier, then we'll need to release more water," Shallcross said. "And so it's really a balance between keeping water in storage for water supplies versus releasing water to repel salinity or to push the salt downstream."

Similar drought conditions pushed the salt front to a similar location on the river in 2016. Keeping the salt line downstream is especially important because there is not ample infrastructure in the region for desalinization to be a viable option if the salt line were to infiltrate the drinking water system in the near future, Shallcross said.

"Eventually, I think with climate change and sea level rise, we'll have to rethink that plan," Shallcross said, adding that water managers will need to look for more storage solutions and other potential options to manage salinity.

More than 14 million people get their drinking water from the Delaware River Basin, including New York City, Philadelphia and surrounding regions, according to the Delaware River Basin Commission. 

If drought conditions worsen, the next step on the contingency plan would be to ask different thermoelectric power generators, which use a lot of water, to either cut back their generation or release water from a storage reservoir specifically for them, Shallcross said.

The step after that would involve asking customers to reduce their water use. But because drought conditions have been worsening in recent months, people are already conserving water, and there may not be much more that households can cut back on, Shallcross said.

The Northeast has seen below-average amounts of rain since September. Despite soaking rain in the last week, drought conditions have not eased much in the region. It was just enough to pause the fire danger and trend of intensifying drought conditions in the region -- for now.

Parts of the Northeast are currently experiencing some of the worst drought conditions in the country, with all of New Jersey and much of eastern Pennsylvania grappling with severe drought conditions or worse, according to an updated map released Wednesday by the U.S. Drought Monitor.

In addition, Northeast reservoirs remain at below-average levels, according to data from the U.S. Geological Survey.

The rain the area received last week made no meaningful change to the Delaware River Basin because most of the precipitation was immediately absorbed into the dry ground, Shallcross said.

And conditions are not expected to improve much in the immediate future. After a storm in the Northeast on Thursday, dry conditions are expected to return. In addition, below-average precipitation is expected for much of the country through early December, particularly in the West, Plains and on the East Coast, forecasts show.

The commission is concerned with the upcoming dry forecast and will be increasing actions if the drought continues to worsen, Shallcross said.

It's possible for the situation to escalate in the coming weeks if ample precipitation is not seen in the region, Shallcross said.

Last year, a similar situation occurred along the Mississippi River, prompting then-Gov. John Bel Edwards of Louisiana to request a federal emergency response as the salt front moved toward New Orleans.

The current drought situation in the Northeast took months to evolve, and it will take several more rounds of significant rainfall over the span of weeks or even months to completely eliminate the widespread drought in the region, experts say.