Louisiana
The mighty Mississippi is now captured and channelized along its entire downstream length, all the way to the Gulf of Mexico.
From high overhead, the Mississippi River Delta resembles a branching set of lungs reaching out into the Gulf of Mexico. The mighty Mississippi is North America’s largest watershed, draining over 40 percent of the continent’s waterways into the Gulf of Mexico. The river’s unusual name comes from the Ojibwa word misiziibi, meaning a river spread over a large area. For at least the past 10,000 years, since the retreat of the last ice age, the Mississippi has emerged from Lake Itasca in northern Minnesota. However, the mouth of the river, where it empties into the Gulf, used to change size, shape, and location constantly, creating a massive delta system.
Deltas form where rivers reach their mouths—at a much larger, slower-moving body of water—and the river drops its load of sediment. Over time, this sediment builds up, creating new landmasses called lobes. These lengthen the river’s path to open water and eventually force the river to change course as it seeks the quickest route to the larger body of water. With its historically high sediment loads, the muddy Mississippi once boasted the seventh-largest delta in the world, but flood control efforts over the past few decades are threatening to destroy the river’s 10,000-year-old balance.
Today the Mississippi is one of the most tightly controlled rivers in the world, with more than 3000 miles of levees—flood control walls—enclosing the river and its tributaries, from southern Illinois to the mouth in Louisiana. But all that flood control is backfiring into an ecological disaster for the Mississippi River Delta.
Before the levee system was installed along the Mississippi’s banks by the Army Corps of Engineers, the river flooded seasonally, redistributing nutrient-rich sediments along the length of the river and revitalizing the floodplains and delta. But these floods also caused death and destruction to people living along the river, and in 1928 Congress passed the Flood Control Act, authorizing construction of a system that would ensure the river never overflowed its banks again.
In this image from space of the Mississippi River Delta, the river’s main channel can be seen breaking into secondary channels as it drains into the Gulf of Mexico. Land and vegetation appear green. Underwater sediment deposits are visible as gray-tan patches; sediment quantities have been significantly reduced since upstream flood controls were put in place.
By the 1980s, the walls (twenty-five to fifty feet high) that make up the world’s largest levee system had completely cut off the Mississippi River from its banks, effectively killing the riparian ecosystem that had flourished for thousands of years. All the sediment that once served as the restorative lifeblood of the “muddy Mississippi” was trapped by dams and levees, starving the river for nutrients downstream.
At the delta, the price of upstream flood control has proved to be astronomically high—since the 1930s, Louisiana has lost nearly 2000 square miles of land, an area about the size of Delaware. Every hour, a football field–sized expanse of wetlands is flooded by open water, caused by the combined effects of reduced downstream sediment, natural subsidence of the delta, and climate-influenced rising sea levels. The environmental consequences are alarming. Many plants and animals struggle to maintain their brackish way of life against the encroaching salt water, and the once-thriving fishing and seafood industries along the coast battle to survive. By some estimates, the Mississippi River Delta could be drowned completely by 2100.
If the Army Corps of Engineers had never exerted their control over the river, the delta would look very different from what it does today. It would be much larger, with many more branches. The additional acreage could have buffered much of the destruction wrought by Hurricane Katrina in 2005, when flood waters topped the levees in New Orleans, killing more than 1200 people and causing more than $100 billion in damage to the city.
You might fly over the Mississippi River Delta en route to New Orleans, Louisiana.
