Yale Environment 360 discusses whether, as sea levels rises, will drinking water supplies be at risk. The Delaware River, a major source of drinking water for Philadelphia, is facing an emerging threat as rising seas push saltwater farther upstream. It’s a problem that other places, from Miami to Shanghai, will also confront, especially as increasing drought lowers river flows.
At the Delaware Memorial Bridge, about 35 miles southwest of Philadelphia, the tidal waters of the Delaware River estuary push upstream with every incoming tide but are opposed by the river’s downstream flow. For years, this balance has kept salty water well away from intakes that supply drinking water to millions of people in Philadelphia and southern New Jersey.
With the so-called salt front in its normal range, some 40 miles downstream from the intakes, any threat to the region’s water supply has seemed distant. But the combination of sea level rise and the expectation of reduced downstream flow as a result of climate change-related droughts have raised new fears that the region’s biggest source of drinking water could at some point become contaminated with seawater. Other regions around the U.S. and the world, from Florida to Bangladesh, are facing similar threats.
The latest projections for sea level rise along the New Jersey coastline are for a gain of up to 1.1 feet between 2000 and 2030, up to 3.5 feet by 2070, and up to 6.3 feet by the end of the century, according to a Rutgers University study. In 2017, the National Oceanic and Atmospheric Administration predicted that the global mean sea level could rise as much as 2.5 meters (8.2 feet) by 2100.
The highest projections have not yet been correlated to the predicted position of the salt front in the Delaware River, according to DRBC’s Shallcross. But in a presentation last October, she said that a 3-foot rise in sea level — roughly equal to the Rutgers forecast for 2070 — would push the salt front about 34 miles upstream from its current position to River Mile 98, only 12 miles downstream of the Philadelphia and New Jersey water intakes.
For its part, the Army Corps is studying whether to expand the designated uses of a Pennsylvania reservoir to allow for its water to be released into the Delaware during times of drought — a potential addition to flows from the three New York reservoirs.