Sensing the swamp beneath the trees

A technique to study land senses water-level changes in the Mississippi River delta.


IN THE mid-1950s, two geologists surveyed the terminus of the majestic Mississippi River, the seemingly endless stretch of interconnected swamps, bayous, and muddy land that comprises southeastern Louisiana. In their report to the United States Army Corps of Engineers, Charles Kolb and Jack Van Lopik described the delta as “a land between Earth and sea–belonging to neither and alternately claimed by both.”

Five decades later, southeastern Louisiana remains in this timeless tug of war between land and water. Residents continue to bury their dead above ground and safe from the shallow water table. In New Orleans, twenty pumping stations drain the land of 85 billion liters (22.5 billion gallons) of water each day. However, the massive artificial levees built to protect communities from seasonal flooding have instead caused the land to be more vulnerable to water. Scientists say the 560 kilometers (350 miles) of levees prevent the river from replenishing the delta with new sediment, causing parts of the land to sink further below sea level. This, and the increase in flooding, have left communities extremely vulnerable to damage from hurricanes, such as Hurricane Katrina in 2005.

Zhong Lu, a physical scientist at the Earth Resources Observation and Science Data Center in Sioux Falls, South Dakota, was drawn to the delta’s unique, if complex, geological processes. Lu was interested in land subsidence, or the sinking of the Earth’s surface in response to geologic or human-induced causes. Lu said, “I wanted to make a map of how land was sinking in and around the New Orleans area using remote sensing. Instead, I saw interesting signals from the delta’s swamps and marshes.” Lu suspected he had found a more efficient way to detect water-level changes, a process that is crucial to flood hazard modeling and wetland management in the delta.

Originally published in Sensing Our Planet: NASA Earth Science Research Features. Read the full story here.

Image courtesy Jan Kronsell.

Story notes

This was my first assignment for Sensing Our Planet, and my first feature-length science story. I didn’t know much about remote sensing and had never been to Lousiana. When I was a beat reporter for the Philippine Daily Inquirer, I had the luxury of visiting my interviewees and even reporting from the place I was writing about. Now I had to write about subsidence—the constant though sometimes imperceptible rise or fall of the ground— happening in a place I know nothing about.

I read everything I could about Louisiana and the Mississippi Delta. I watched documentaries and listened to music from the region (which is how I discovered the music of Tab Benoit). It was overwhelming. And after interviewing Zhong Lu, my brain was drowning in technical details. I might have cried at my desk.

After more searching, I finally found a reference to a report by the U.S. Army Corps of Engineers describing the Mississippi River Delta as “a land between earth and sea–belonging to neither and alternately claimed by both.” It was the perfect quote to illustrate the real-life presence that subsidence imposes in the delta. I found more details about the constant pumping New Orleans needs to do drain the land. I learned about floating coffins. I finally had the gritty real world details to flesh out the story of Lu’s work. When you have a vivid, even visceral, image or metaphor to illustrate the main science concept in your story, you are set.

Want to read more about metaphors in science writing? Astronomer Caleb Scharf defends it in this Scientific American essay. In this New York Times essay, NatGeo writer Michelle Nijhuis says science writing needs to explain things “with both maximum simplicity and maximum accuracy.” She quotes George Johnson, “The goal is to show how some new discovery looks to an interested outsider, writing for other interested outsiders, using metaphor instead of mathematics.”