21 August 2015 (Sky News US) – Engineers have said that part of the Mississippi delta must be left to deteriorate completely if New Orleans is to be saved from another powerful hurricane.
Thousands of miles of wetland between the city and the Gulf of Mexico, which once provided a natural buffer to surges created by storms, have been damaged by levees and navigation channels, Scientific American says.
An article in the magazine states that the levees, built by the US Army Corps of Engineers, have prevented flooding to farms, industry and towns along the lower Mississippi River.
But they have also stopped vital silt and freshwater needed by plants, which formed a natural barrier to storm surges, from thriving in the wetland in the 40 miles between New Orleans and the gulf.
The magazine states: "Unless the rapidly disappearing wetlands are made healthy again, restoring the natural defence, New Orleans will soon lay naked against the sea.
"Let the badly failing wetlands there completely wither away, becoming open water, so that the upper parts of the delta closer to the city can be saved."
Three international engineering and design teams that won the Changing Course Design Competition have said the mouth of the Mississippi River, known as the bird's foot because of its shape, must be left to die. [more]
By Mark Fischetti
20 August 2015
(Scientific American) – Hurricane Katrina demolished New Orleans 10 years ago, a grim anniversary to be marked next week. Huge earthen levees dissolved and concrete floodwalls toppled over. But the real culprit when the tropical cyclone made landfall was outside the city. Thousands of square miles of wetland marshes and swamps that had once provided a buffer between the city's coastline and the ocean had been badly tattered from decades of human damage. Thick, robust wetlands would have absorbed much of the surge of water that Katrina pushed up from the Gulf of Mexico. But levees had starved the wetlands of needed nutrients, making plants weak, and thousands of miles of manmade canals had torn the vegetation apart, allowing Katrina’s onrushing storm surge to flow right into New Orleans.
Extensive studies done after Katrina verified what lifelong residents of southeastern Louisiana already knew: Unless the rapidly disappearing wetlands are made healthy again, restoring the natural defense, New Orleans will soon lay naked against the sea (see satellite image, below).
So, how does one reengineer the entire Mississippi River delta—one of the largest in the world—on which New Orleans lies?
Three international engineering and design teams have reached a startling answer: leave the mouth of the Mississippi River to die. Let the badly failing wetlands there completely wither away, becoming open water, so that the upper parts of the delta closer to the city can be saved. The teams, winners of the Changing Course Design Competition, revealed their detailed plans on August 20. Graphics from each plan are below.
Scientists worldwide agree that the delta’s wetlands disintegrated because we humans built long levees—high, continuous ridges of earth covered by grass or rocks—along the entire length of the lower Mississippi River. The leveed river rims the southern boundary of New Orleans and continues another 40 serpentine miles until it reaches the gulf. The levees, erected almost exclusively by the U.S. Army Corps of Engineers, prevented regular floods from harming farms, industries and towns along the river’s course. However those floods also would have supplied the brackish marshes with massive quantities of silt and freshwater, which are necessary for their survival. [more]