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Wetland Solution to Mississippi River Flooding

Wetlands Mississippi River

In recent days, flooding along the Mississippi River showed how spillways play a role in relieving pressure on levees and dams. But did you know that wetlands naturally do the same thing?

Just as a spillway is the last line of defense for levees and dams before the water overflows, wetlands act as a buffer, relying on greenways for the same gradual release of water into the ocean. It functions just like the overflow drain near the top of your bathtub or sink. Except that during a high water event today, the spillways of manmade dams and levees have now taken the place of wetlands nearly everywhere along the Mississippi.

Why levees?

French settlers built the earliest levees to save New Orleans from the Mississippi and as a means of harnessing the river’s power for transportation, commerce, industry and agriculture. By 1882 the original, unorganized levee system was turned over to the U.S. Army Corps of Engineers, and they continue to manage the system to this day.

Earlier this month, the Corps blew up man-made levees and flooded low-lying farms to save the town of Cairo, Illinois, from flooding. A healthy wetland would have absorbed that deluge, been strengthened by a new layer of river sediment, and then slowly released cleaner water back into the river—preserving the integrity of the local lands and those near the Gulf of Mexico. In fact, under natural conditions, wetlands would have been doing this continuously over the decades and not just during a catastrophic flood year like this one.

Where did the wetlands go?

Further down the Mississippi River, wetland loss along the Louisiana coast has long been recognized as one of the state’s most pressing environmental problems. The levee system that was developed in the waterways of the Mississippi River and surrounding tributaries for flood control has had major impacts on wetland loss. Historically, the river overflows in the spring spreading fresh water, nutrients, and sediment to the coastal zone. With the levees in place, the overflow was blocked or diverted and the existing soil slowly washed away, starving the wetlands of rich sediment. Flood sediment was then sent directly into the Gulf of Mexico, bypassing all the wetlands upstream.

The value of wetlands

Healthy wetlands deliver many services that support our economy in ways most of us take for granted—until faced with the choice of flooding major cities like Baton Rouge and New Orleans or washing out working farms and valuable oyster beds. One study by Earth Economics, published shortly before the BP oil spill, valued the Mississippi River Delta’s natural services at almost $47 billion annually.

Wetlands not only give water a place to go when a river swells beyond its capacity, they also filter the water and provide shelter for migrating birds, juvenile fish, and other animals.

In terms of benefits to humans, wetlands provide critically needed flood control, water filtration, carbon sequestration, scenic beauty, and recreation. But only if they are allowed to remain in place to do so.