Growing Louisiana deltas make for a rare phenomenon – NASA studies the coastline

A satellite view of the Louisiana coastline. The two growing deltas, Wax Lake and Atchafalaya, are circled in red. (Image courtesy: USGS/NASA)

 New Delhi: NASA just observed a rare phenomenon – within the sinking Louisiana coastline under the Gulf of Mexico, scientists have observed two growing river deltas.

The Louisiana coastline is sinking at the rate of about one football field of land every hour (about 18 square miles of land lost in a year), whereas the Atchafalaya River and its diversion channel, Wax Lake Outlet, are gaining about one football field of new land every 11 and 8 hours, respectively (1.5 and 2 square miles per year).

As per NASA, The basics of delta building are understood, but many questions remain about how specific characteristics, such as vegetation types, tides, currents and the shape of the riverbed, affect a delta’s growth or demise. That's partly because it's hard to do research in a swamp.

"These factors are usually studied using boats and instruments that have to be transported through marshy and difficult terrain," said Christine Rains of the Jet Propulsion Laboratory (JPL), an assistant flight coordinator for the program. "This campaign was designed to show that wetlands can also be measured with airborne remote sensing over a large area."

In order to keep track of subsidence (sinking) and changes in levees, the JPL team flies over the Louisiana coastline at least once a year. The most recent airborne flights, however, focused on the growing deltas – specifically, flowing water and vegetation.

JPL's Marc Simard, principal investigator for the campaign, explained that on a delta, water flows in every direction, including uphill. "Water flows not only through the main channels of the rivers but also through the marshes," he explained. "There is also the incoming tide, which pushes water back uphill. The tide enhances the flow of water out of the main channels into the marshes," NASA reported.

When the tide goes out, water drains from the marshes, carrying sediment and carbon.

The space agency explained the entire process of the study saying that, the JPL instruments took measurements during both rising and falling tides to capture these flows. They also made the first complete measurement of the slope of the water surface and topography of the river bottom for both rivers from their origin at the Mississippi River to the ocean – necessary information for understanding the rivers' flow speeds.

Furthermore, three JPL airborne instruments, flying on three planes, were needed to observe the flows and the movement of carbon with the water. The team measured rising and falling water in vegetated areas using the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) instrument. They measured the same changes in open water with the Airborne Snow Observatory (ASO) lidar. The Airborne Visible/Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) was used to estimate the sediment, carbon and nitrogen concentrations in the water, NASA said.