The Widening of Neptune Pass

#Seas & Oceans, #NASA, #Landsat, #Image in the news

Published on 20 March 2023

Over the past six years, what was once a small canal on the east bank of the Mississippi River has widened to become a major channel, with a flow five times that of New York’s Hudson River.

The channel, called Neptune Pass, is about 25 miles (40 kilometers) upriver from where the Mississippi empties into the deep waters of the Gulf of Mexico. The channel now delivers freshwater and sediment into the shallower coastal waters of Quarantine Bay and Bay Denesse, much closer to New Orleans.

“This is the biggest branch of the river to open up in almost a century,” said Alex Kolker, a coastal geologist at the Louisiana Universities Marine Consortium.

Neptune Pass can be seen cutting through the wetlands on the east bank of the Mississippi River in the image above (right). The image was acquired by the Operational Land Imager (OLI) on Landsat 8 on February 6, 2023. It shows a plume of sediment fanning out across Quarantine Bay, an inlet between the coast and the Gulf of Mexico. The image on the left shows the same area in 2019, before the canal widened.

Kolker noticed Neptune Pass while looking through satellite imagery in the early days of the COVID-19 pandemic. “I looked at different passes in the region, including Mardi Gras Pass and the crevasses near Fort St. Phillip,” Kolker said. “But in the middle of those two, I noticed an existing canal had significantly widened.”

What had been a 150-foot canal in 2016 had widened to become an 850-foot-wide distributary in 2023, with a flow of over 118,600 cubic feet (3,360 cubic meters) per second, about 16 percent of the Mississippi’s total flow. Kolker thinks the widening may have been a response to several years of high river flow, especially during the major flooding that occurred along the Mississippi in the spring of 2019.

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NASA Earth Observatory. (2023, March 20). The Widening of Neptune Pass.