SCOTT SIMON, HOST:
As the climate gets warmer, dirt is becoming a hot commodity. Coastal cities use it to protect themselves from rising seas by building levees and restoring marshes. But supplies are getting tight, as NPR's Lauren Sommer reports.
LAUREN SOMMER, BYLINE: There's a name for Pat Mapelli's job, a name he's not really a fan of. He's considered a dirt broker.
PAT MAPELLI: I hate that name. I'll be honest with you. Dirt just has that negative connotation. You know, you got to go wash up, right?
SOMMER: Because what Mapelli handles is in high demand. He works for the construction materials company Graniterock. And he gets a lot of phone calls about dirt.
MAPELLI: Oh, the demand is way beyond what the supply is.
SOMMER: We're walking on top of one of the deals that Mapelli brokered. It's an earthen levee on the shores of San Francisco Bay, one that helps protect hundreds of thousands of people. Over the years, waves and weather have worn it down.
MAPELLI: It's very much lower than it should be right now.
SOMMER: It needs more dirt, and a lot of it - 1 million cubic yards for the levees in this area. That's 100,000 dump trucks. So Mapelli is a matchmaker. He finds people who need to get rid of dirt, like a construction project that's digging an underground parking garage, and he finds a way to get that dirt to the shoreline. With sea level rise, the need for that is only going up.
LETITIA GRENIER: How do we get people to see that we're on the precipice of a huge crisis?
SOMMER: Letitia Grenier is a senior scientist at the San Francisco Estuary Institute, an ecological science group. We're standing next to a marsh that's a magnet for wildlife.
GRENIER: Right now, we're looking at water birds from basically all over the Western Hemisphere.
SOMMER: This muddy stretch of low-lying plants is also a barrier against the water.
GRENIER: These marshes are knocking down the waves. They're absorbing the water. And they're really helping create flood risk management along the shore, which is critical for many billions of dollars of infrastructure, as well as neighborhoods and other communities along the shoreline.
SOMMER: Grenier says about 90% of the bay's marshes have been filled in. A lot need to be restored to protect the shoreline from rising seas, which could go up between 3 and 6 feet by the end of the century. But even after they get restored, the marshes will still need mud to keep up with sea level rise. The muddy water that comes in with every tide helps build it up.
GRENIER: If the wetlands don't have that, they basically drown. They get lower and lower relative to how high the water is.
SOMMER: Grenier and her colleagues found that San Francisco Bay will likely need more than 500 million metric tons of sediment by the end of the century to deal with climate change. The natural supply will fall short of that, only one-third to one-half of what's needed. But there is a potential source of mud just nearby.
Every year, thousands of ships come into San Francisco Bay following navigation channels. The federal Army Corps of Engineers is responsible for dredging them, collecting millions of cubic yards of mud every year. Tessa Beach, who works at the Corps' San Francisco district, says they do get requests to use that mud for restoration projects.
TESSA BEACH: I don't disagree. I think, you know, dredge material should be viewed as a really valuable commodity in that regard.
SOMMER: But she says federal rules require them to pick the cheapest option to get rid of it, which usually means just dumping it, often out in the Pacific Ocean.
AMY HUTZEL: It is frustrating that this has been decades of trying to solve this problem.
SOMMER: Amy Hutzel is with the California Coastal Conservancy, a state agency that works on restoration. She says the only way for states to get this dredged mud is to pay the extra cost of moving it. Dumping it may be cheaper, but that ignores the longer-term benefits of preventing flooding, she says.
HUTZEL: So we're just going to be seeing erosion of our shorelines and mudflats and marshes unless we start doing things differently with sediment.
SOMMER: That could be changing soon. Last year, Congress passed a law that told the Army Corps of Engineers to consider the environmental benefits of using mud, including to prepare for climate change. The agency says it plans to release new rules on using mud by August.
Lauren Sommer, NPR News.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.