Building a series of new sediment-diversion structures the lower Mississippi River delta that would be opened during floods to "pulse" large volumes of sediment into eroding parts of southern Louisiana would be an excellent and worthwhile use of limited federal dollars, a group of engineers and coastal scientists said in a report issued in mid-April.
The Mississippi River Delta Science and Engineering Special Team, which produced the report, said that careful engineering of a multibillion-dollar diversion plan would help ensure that the government's ongoing efforts on flood control and maintaining navigation on the lower Mississippi would be enhanced, not hurt.
The team, which prepared the report for the National Audubon Society, the Environmental Defense Fund and the National Wildlife Federation, noted that due to rising energy costs it would be best for any plan to make maximum use of gravity, water flows and other natural forces, and to do as much of the needed construction sooner rather than later.
"The navigation system on the lower Mississippi is fragile, and there's a real chance that if something isn't done the river could jump out of its course and shut down [navigation on] the river for months," John Day, the team's chairman and professor emeritus at Louisiana State University, said in an interview.
Day said the construction of several diversion structures along the river upstream from New Orleans would relieve pressure on the existing levee system and enable the occasional diversion of sediment-laden floodwaters into other pathways to the Gulf of Mexico. That, he said, would help to replenish coastal wetland areas that have been disappearing an an alarming rate in recent decades due to the levee system that now flushes most sediment out to sea and, more recently, to climate change.
Day and Angelina Freeman—a co-author of the report and a coastal scientist at the Environmental Defense Fund—both pointed to the 80-year-old Bonnet Carré Spillway as just north of New Orleans an example of how the proposed diversion structures would work. They noted that the structure has been opened only about once a decade since it was built after the Mississippi River's infamous 1927 flood, but has contributed substantially to the rebuilding of downstream wetlands.
Freeman said that by diverting large amounts of sediment from the main river channel, the diversion projects also would make it easier to maintain the channel depths needed to handle barges laden with coal, grain and other commodities.
Day and Freeman also said that they agreed with most elements of Louisiana's planned 50-year, $50-billion coastal management plan. That plan said that the state's modeling "showed that marsh creation projects located near a sediment diversion were more sustainable after 50 years than the marsh creation project alone."