What: A huge man-made canal that counteracts coastal erosion
Where: Louisiana coast
Cost: $2 billion â€ $3 billion
Crux: A 1,000-foot-wide, 60-foot-deep channel off the Mississippi River capable of carrying 200,000 cubic feet of water per second over 100 miles.
What years of engineering efforts have destroyed, engineers will now endeavor to repair. For eons the great muddy Mississippi River deposited sediment at its delta, replenishing any eroded areas and creating a rich incubator of barrier islands and bayous that nourished shrimp and shellfish and protected the low-lying coast from hurricanes and flooding. But oil and natural-gas industries dug channels throughout the delta to lay pipe, and the Army Corps of Engineers built levees along vast stretches of the river to control its water levels. The channels caused swifter-than-natural erosion, and the levees limited any chance of recovery by diverting much of the river’s silt to a single outlet. Today millions of tons of sediment simply vanish off the continental shelf deep in the Gulf of Mexico, and, no longer nourished, Louisiana’s famed bayous are disappearing faster than any other ecosystem on Earth.
The proposed fix is, ironically, another ditch: the Third Delta Conveyance Channel, a 30-to-40-foot-deep, 350-foot-wide, 100-mile-long channel off the Mississippi that will transport 20,000 cubic feet of water per second into the Gulf. Over 20 to 60 years, the channel is supposed to erode until it’s 1,000 feet wide, 50 to 60 feet deep, and flowing at 200,000 cubic feet per second, delivering enough sediment to rebuild the marshes around Louisiana’s barrier islands. “Most diversions drop sediment along their route rather than carry it to where it needs to go,” says Bob Roberts, Louisiana State Department of Natural Resources manager for the project. “That’s why we need such a big, high-velocity channel. Will this thing erode like we want it to, and then can we control it? We still don’t know.”