In a hotter climate, dirt is a hot commodity.
With sea levels expected to rise three to six feet by the end of the century, coastal communities are moving fast to construct major shoreline projects to protect themselves. As the size of these projects expands, the primary building materials–dirt and mud –are getting scarce.
Dirt (what you dig up on land) and mud or sediment (the wetter variety already in rivers and bays) are the raw materials of climate change adaptation. They’re used to build levees, the massive earthen barriers that hold back waves, and to raise elevation so buildings can sit higher than the floodplain.
Mud is also a crucial component of restoring wetlands and marshes, which act as natural barriers against storm surges while providing valuable habitat for sensitive species. In the right conditions, marshes can gain elevation over time from sediment, potentially keeping pace with sea level rise in a way that human-built infrastructure can’t.
Until now, mud and dirt have mostly been treated as waste products. Dirt leftover from construction projects is often just trucked to landfills. Sediment is trapped behind large dams, no longer spreading naturally throughout watersheds.
Sediment is also dredged from shipping channels every year, but little is reused to adapt to climate change. The U.S. Army Corps of Engineers runs dredging operations, but its disposal policies mean that around 140 million cubic yards of sediment are dumped annually, even as restoration projects clamor for material.
Environmental experts warn that unless coastal regions from San Francisco Bay to the Mississippi River Delta begin managing their dirt and mud supply more comprehensively, the shortfall will be severe, leading to more expensive sea level rise protection and drowned wetlands.
“We’re on the precipice of a huge crisis,” says Letitia Grenier, senior scientist at the San Francisco Estuary Institute, a water and ecology think tank. “If we act now, we actually have enough sediment from other sources to keep our wetlands and to keep protecting our shorelines. But if we keep doing business-as-usual approaches, we’re going to be in really big trouble.”
Call the dirt broker
In a warming climate, there’s a job in high demand that comes with an unglamorous name: “dirt broker.”
“I hate that name,” says Pat Mapelli, land use manager and bay restoration lead at Graniterock, a construction materials company. “I’ll be honest with you. Dirt just has that negative connotation.”
Mapelli is a highly sought-after terrestrial matchmaker. He brokers deals between those who need dirt and those who want to get rid of it. These days, his phone is ringing more often with requests he can’t fulfill.
Dredging ships remove more than two million cubic yards of sediment from San Francisco Bay shipping channels ever year.
U.S. Army Corps of Engineers
“The demand is way beyond what the supply is,” he says, walking on an earthen levee on the eastern side of San Francisco Bay, a project he’s putting together.
This part of the bay was once used for industrial salt making, and giant evaporation ponds were built here more than a century ago. Now, its marsh habitat is being restored as part of the Eden Landing Ecological Reserve. The old salt pond levees still stand between the bay and hundreds of thousands of people on the shoreline. But waves and weather have eaten away at them.
“It’s very much lower than it should be right now and very much narrower than it should be right now,” Mapelli says, looking at a stretch of levee bordering the blue, flat water of the bay.
Over the next several years, one million cubic yards of dirt will be brought to this site to build up the levees — the equivalent of 100,000 dump truck loads. Most comes from local construction projects doing excavation for foundations or underground parking garages.
Still, not all dirt is good dirt. Some of it contains pollutants or naturally occurring metals. Other loads are too far away, making the cost of trucking prohibitive. And often, construction companies want the fastest and cheapest solution, which means taking dirt to a landfill.
Mapelli knows the market for his services will only get stronger as more cities grapple with the fact that their shoreline infrastructure is being quickly overwhelmed by climate change. But the supply crunch has already hit.
“You’re starting to look at all the edges around the bay and there’s a lot of these projects,” he says. “But it takes material. It takes dirt.”
