Shifting Sands in the Bayou

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Published on October 15th, 2012  |  Discuss This Article  

When you are in Louisiana’s Atchafalaya River Basin, it is easy to feel as though this is a place where time stands still, where nature is and always has been the dominant force, and where contrasts do not exist. Indeed, as I look around me, it is a world of water, bottomland hardwood forest and iconic cypress swamp.

But then we come to a junction where the sluggish and winding bayou intersects with the straight and geometric—a man-made canal, dredged for oil and gas development some decades before. So this seemingly wild place has not escaped human’s designs after all—in fact, it is full of these kinds of stark contrasts. Welcome to the Atchafalaya Basin, one of the least-known important places to people in the United States.

Since disastrous 1927 floods that displaced hundreds of thousands along the Mississippi River and its tributaries, this 1-million-acre wilderness of bayous and trees has also been a major component of the nation’s defenses against flooding. And since the Atchafalya was declared a federal floodway, the water and sediment that created and sustain this majestic landscape have been highly altered by major flood protection levees, channel engineering and the construction of the Old River Control Structure that keeps the seasonal rise and fall of water in the basin sort-of-(but not quite) normal.Today, the resulting management issues in the basin seem as numerous as the modifications made here over the past century for flood control, navigation and industry.

In early April, I was fortunate to tour a portion of the Atchafalaya Basin with scientists from TNC and USGS to get a handle on just one of those management issues—sediment dynamics in this highly impacted riverine wetland. To most, sediment may not be as awe-inspiring as the bald eagle we spotted flying over the cypress trees…but in the Atchafalaya and coastal Louisiana, sediment is a big deal, and it keeps coming.

My past training and research has focused on how rivers evolve over long time periods (thousands to millions of years), so it is exciting to be in a place where the Mississippi River has changed courses numerous times throughout the Holocene, building the state of Louisiana in the process. But as a Ph.D. student (and Louisiana outsider) now working on science and policy issues in this Basin, I have to overcome my tendency to look at this river from the geologic time-scale perspective, because this place is no longer operating totally naturally—with big consequences for people who have deep roots here.

If you check out the USGS map of coastal land loss since 1932, it is quickly apparent that in most places in coastal Louisiana, the problem is too little sediment. But the Atchafalaya Basin is the one part of Louisiana that is actually gaining land. Great, right? Well, that depends on your perspective. Many families that used to live in the Basin and now have settled outside of the protection levees still consider the Basin home and depend upon it for their livelihood. In a lifetime (since the 1930s), they have witnessed dramatic changes that have taken place, as sand and silt convert the once vast expanses of open water in the Basin to land.

It’s hard to travel across land in a boat and even harder to fish on it. While this process was already occurring before the levees and Old River, conversion inside the floodway ramped up after they were installed. Such changes, whether ultimately caused by people, nature, or some combination of both, have the power to create strong emotions, blame and behavior that ultimately may make problems worse. I witnessed this type of behavior first-hand on my recent trip.

During the 2011 floods, some people still unknown intentionally removed both an earthen and heavy steel blockage from a pipeline canal that used to connect a place called East Grand Lake, a once expansive lake, with the main Atchafalaya River channel. These blockages were placed there to keep the river’s sediment from rapidly filling the lake through this canal—a good thing for the lake, but a bad thing if you want to have a direct route to access the lake from the main channel. This was likely a case of “blockage gone equals shorter route.” But with that new, shorter route comes sediment—a bad thing for the lake.

When we approached the outlet of this re-opened channel, the flow into the otherwise still lake was perceptible—and as we entered the channel, our boat was tossed about by the current. The channel had almost tripled in width since last year, and we had no trouble proceeding in a boat that was 8 feet wide. With the exception of the main river channel, these were by far the greatest velocities we witnessed that day in this land of lazy, winding bayous, and the mobilized sediment in that water is now forming a new delta (land) in East Grand Lake. One or two people acting alone have sped up a geologic process in this part of the world. And ultimately, if this new channel is not blocked, the price of that shorter boat ride now will be a shorter life span for East Grand Lake.

Does this contrast matter in such an altered landscape, since Grand Lake’s historical extent has already been reduced dramatically? Ultimately, these are the kinds of questions facing those in the Basin. It matters if you remember fishing there with your grandfather as a kid. It matters if you are a fish seeking refuge when water quality deteriorates during a hurricane. Eventually, the Mississippi River will go where it wants. But until that time, the contrasts in the Basin will need to be managed—hopefully in ways that will maintain healthy ecosystems that serve the nation as well as the inhabitants of the Basin.

Anne Hayden is a Ph.D. student in Environmental Resources and Policy at Southern Illinois University and an intern with The Nature Conservancy. Her research interests include Quaternary geology, fluvial geomorphology, GIS, modeling and science communications. She is a recipient of a prestigious NSF-IGERT fellowship.

(Image: Lake Chicot, Louisiana. Since the early 1900s the lake has  infilled rapidly with sediment. Source: Anne Hayden.)

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Comments: Shifting Sands in the Bayou

  •  Comment from Allison Voglesong

    Interesting new developments! I had the opportunity to help the Louisiana bayou from suffering this very problem. I was volunteer with National Relief Network and we worked with LSU Extension planting bald cypress trees in sensitive areas. Over only 3 days we planted tens of thousands of bald cypress trees. I got to see a silty canal up-close and personal, and I sure couldn’t see any fish from where I stood on the banks of the canal. Haven’t been to East Grand Lake specifically, so I am interested to learn about the delta development issue there as it’s new to me. Keep up the great coverage!

  •  Comment from Johnny Armstrong

    Great work, Ann! Talented young scientists like you give me hope. Thank you. Thank you!

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