Sea level rise may swamp many coastal U.S. sewage plants

Source(s): Eos - AGU

Cities typically build wastewater treatment facilities in low-lying areas. A new national study identifies which plants are most vulnerable to coastal flooding.


Raw sewage gets people’s attention, but sea level rise, with its distant time horizons, not so much. What if I told you that sea level rise could cripple wastewater treatment plants in many coastal cities and send untreated sewage into nearby rivers and seas? Are you listening now?

According to a new assessment of U.S. sewage treatment plants, the next 1 foot (0.3 meter) of sea level rise, expected along U.S. coasts as soon as 2030, would leave more than 1.5 million people in California, New York, and Virginia without wastewater treatment services.

Consulting a national database of wastewater treatment facilities, researchers from the University of California, Berkeley, flagged those whose locations and elevations made them vulnerable to sea level rise and coastal flooding.

“We found that almost all coastal cities in the U.S. will experience some impact if no action is taken to protect them,” environmental engineer and lead researcher Michelle Hummel told Eos. Previous studies have primarily focused on specific regions.

Affecting Millions

To give the impacts of sea level rise a human scale, Hummel and her team recorded the number of people served by each vulnerable treatment facility. “Population-wise, California and New York could have millions of people who would lose access to wastewater services,” said Hummel. Countrywide, a 3-foot sea level rise would result in a loss of wastewater treatment services for 8.4 million Americans. At 6 feet, the number jumps to 27.8 million, the team’s tallies show.

Prior research into the effects of sea level rise had not quantified the number of people who would lose services in various sea level rise scenarios, Hummel said. She presented the study’s results Monday at the American Geophysical Union’s 2017 Fall Meeting in New Orleans, La.

Rising Vulnerability

Gravity dictates that it’s easier and cheaper to pump sewage downhill. This simple fact means that most of the nation’s wastewater treatment plants are built at low elevation. It’s also easier and cheaper to get rid of treated water if a large body of water is nearby, and on the coasts this typically means the oceans. This combination makes wastewater treatment plants, and the vital services they provide, vulnerable as sea level rises.

Flooding from sea level rise disables wastewater treatment plants by filling tanks and critical components with water. That water takes up more and more space in the tanks until it causes the worst kind of traffic jam. Effluent that normally would have been cleaned by the plant gets redirected to the local overflow destination. In New York City, Hurricane Sandy sent 10 billion gallons of sewage into the East River, the Hudson River, and New York Harbor.

Permanent inundation from sea level rise remains on the horizon, but storm surges and coastal flooding are becoming more frequent today. This year, Hurricane Harvey shut down 40 wastewater treatment plants in the Houston, Texas, area. Increased coastal erosion is rasping away what is often a thin strip of land separating many of these facilities from the water.

Consequences Beyond the Coast

Wastewater treatment plants are often multimillion-dollar facilities serving sprawling metropolitan areas. This means that the loss of a treatment plant can affect communities that on a map might look safely ensconced from sea level rise. In Massachusetts, for instance, the Deer Island Wastewater Treatment Plant, which juts into Boston Harbor, serves more than 2 million people in 43 communities of the surrounding Boston area.

The new analysis “blows the whistle for a large number of states and cities across the country,” said Gary Griggs, a coastal scientist from the University of California, Santa Cruz, and member of a working group updating the state of California’s sea level rise guidance documents. “The fact that [the assessment] is nationwide is a big step forward, and the fact that they’ve looked at a whole range of sea level rises enables individual states to pick and choose.”

Cities need to think about how these threats progress over time to prioritize climate change adaptation strategies, the study authors reported.

Groundwater Flooding in the Bay Area

Groundwater levels on the coasts and along rivers linked to the oceans are predicted to rise along with sea level. In some locations, this can mean that the greatest threat to infrastructure may come not from waves crashing over seawalls but from water bubbling up from below.

The availability of detailed groundwater data for the San Francisco Bay Area allowed the researchers to identify three wastewater treatment facilities vulnerable to flooding from rising groundwater. This threat from below could disable these plants many years before they are inundated by rising sea levels, the team reported. In their plans to protect their key facilities, many cities have neglected threats from groundwater, said Hummel.

The study found that within California, the Bay Area’s wastewater treatment plants are particularly vulnerable. Of the treatment plants expected to experience flooding in coming years, 80% were located in the Bay Area, particularly in the South Bay.

“They say you should hope for the best and plan for the worst,” said Griggs. “But in many cases, we haven’t planned for the worst—we need to.”

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