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When Flood Protections Falter
The following is a guest post from NWF Coastal Analyst, Alisha Renfro.
Large amounts of rainfall and snowmelt throughout the Midwest caused the Mississippi River to swell to record conditions, the biggest flood below Memphis since the great flood of 1927, leaving in its wake extensive flooding. Here in southern Louisiana, the crest of this flood is just now reaching us. Many people in the Atchafalaya River basin have been forced to evacuate.
In the meantime, those living under the protection of the levee system are left to wonder if the current management of the river is really the best way, because while the levees protect from floods, they also deprive delta wetlands of life-giving sediments. Though people may survive the river flood, their protection from hurricanes crumbles as the delta disappears around them
Meeting people in a parking lot at 7:30 a.m. is not usually my favorite way to start off a Saturday, but I had an opportunity last weekend to see the Mississippi River as it may have been 200 years ago. As a scientist that was chance I just couldn’t miss. Along with researchers from the Lake Pontchartrain Basin Foundation (LPBF), I headed down to Bohemia, which sits on the east bank of the lower Mississippi River. It is a section of the river where no levees exist, and the forest and marshes are only separated from the river by a natural low ridge built by the river itself as it deposited sediment during previous floods. Even under the high-water conditions that occur every spring, the ridge usually keeps the river separate from these habitats, but when the river reaches flood conditions it overtops the ridge, delivering much-needed freshwater, nutrients and sediment to the wetlands.
While his researchers waded in the water rushing from the river to survey along the gravel road that runs through Bohemia, Dr. John Lopez of LPBF gave me a tour of the area. John and his group are trying to understand how the water flows through this un-leveed area when the river is high and if this periodic connection to the river is the key to the extensive and lush marshes that can be found here. North of here, the river is straitjacketed by artificial levees, leaving the wetlands of the delta cut off from the freshwater and sediment that is critical for their continued survival. As a result, these coastal areas are disappearing at a rate of a football field every 38 minutes, taking with them essential habitat for birds and fish, as well as the livelihoods of many residents in southern Louisiana.
Soon I got a chance to wade down the gravel road and participate in the some surveying myself. There were several places where the river was flowing so quickly over the road that I had to be careful to stay on my feet. If there was any doubt left in my mind, this experience showed me that the Mississippi is still mighty and capable of remarkable destruction.
The current method of river management is to build higher and higher levees to funnel water down the river and past communities. A few key spillways offer safety valves, shunting water away from densely populated communities during big floods like this one.
But this method leaves us one accident, one levee failure away from catastrophe. Instead, we can continue to use a levee system, but also restore the natural defenses along the river’s floodplain. In Louisiana this means reconnecting the river with its delta through controlled openings – diversions – that during high river flow can deliver water, sediment and nutrients to delta wetlands, strengthening the ecosystem. These openings will also provide more safety valves for shunting water and reducing the strain on the levee system that protects communities.