Much of greater New Orleans has been naturally sinking for generations. But scientists don’t know a lot about why, where, or how fast it’s happening. So now, they’re looking below the streets for clues -- at the layers of dirt, sand, and mud. The city hopes it’ll help us prepare for the future.
In a grassy park in the Gentilly neighborhood of New Orleans, a group of scientists are standing up and twisting a big piece of metal into the ground.
“It's like a really long and complex corkscrew,” says Alex Kolker, coastal scientist with both Tulane University and the Louisiana Universities Marine Consortium (LUMCON).
He and the others are using the instrument, called an auger, to dig deep into the ground and pull up soil samples. It turns out there’s a lot we don’t know about the dirt and water beneath our feet. Roelof Stuurman a researcher with Deltares, a research group from the Netherlands that specializes in water management and soil science, says there’s a “lack of groundwater information in the city.”
“And in this week, we want to make as many possible [sample] holes to determine the groundwater level,” says Stuurman. “This is very important to determine the risks for subsidence,” he adds.
Subsidence is the natural shifting and sinking of the soil, and it’s happening all over the city. It can cause water pipes to break, potholes to form in the street, and can crack the foundation on your home. Understanding what’s in the soil -- and how deep the water table is -- tells us where, why, and how fast certain parts of town are sinking.
The team turns the auger, pulls up some dirt, and examines it. Tulane PhD candidate Molly Keogh points at the discarded soil samples, noting how the colors have changed as they’ve dug deeper. Some are dark brown. “That is all clay material,” she says. The samples with lots of sand are much lighter.
Somewhere around the seven foot mark they hit water. The team gets excited when the auger comes out with a suction-y slurp.
This borehole is just one of 75 sites sampled across town last month. The ultimate goal of the research is to create a three dimensional model of the the soil and water under New Orleans. Kolker says that’ll help the city better understand the present situation, as well as what to expect in the future.
“It might help us predict where where New Orleans is going to be 10, 20, 50 years in the future as [the city] continues to sink,” he says.
And that’s exactly why the city asked for this research; to bring things into focus.
“You might think of it like like a photograph,” Kolker says. “I think we had a good enough grainy photograph to have an understanding of what the picture looks like. And hopefully this will make it a little more high-def.”
Tyler Antrup, Urban Water Program Manager for the City of New Orleans, says this high-def image will help the city make big decisions. Deciding things like what kind of foundation to use for a building or roadway, or where to store water in the soil.
The city wants to rely less on mechanical pumps and canals to get rainwater off the streets. It wants to build more detention ponds and rain gardens in sandy places, since sandy soil absorbs water better than soil with lots of clay.
“So we may want to look at places where we have those large sand layers, so we can actually, you know, retain the water there,” says Antrup.
Meanwhile, the water keeps coming.
Clouds are moving in and the sky is getting dark. So the team collects their tools, piles into a minivan, and drives off toward next site -- hoping to beat the rain.
Support for the Coastal Desk comes from the Walton Family Foundation, the Greater New Orleans Foundation, the Foundation for Louisiana, and local listeners.