This piece was originally posted on National Wildlife Federation's Wildlife Promise blog.
By Maura Wood, National Wildlife Federation Coastal Louisiana Senior Outreach Coordinator
Our boat left the canal, rounded a small spit of land, and emerged into the outfall area of the Caernarvon freshwater diversion, known as Big Mar – Big Sea. Situated in the last big bend of the Mississippi River about a half an hour drive south of New Orleans, this failed agricultural enterprise of the past shows up on satellite photos as a big square lake. Recent imagery had suggested that perhaps some mud shoals had developed as a result of the diversion.
But today, I wasn’t looking at mud shoals. I was looking at acres of bushy, green, growing, happy vegetation. This couldn’t be Big Mar. This was “Big Mar-sh”!
Caernarvon is the diversion everybody loves to hate. “It doesn’t work,” they say. “It hasn’t built land. What good is it?”
I always sigh when I hear that. Diversions should be a way of reconnecting the water and sediment of the Mississippi River, constrained within levees, with the nearby marshes which, pre-levee, were built and sustained by annual flooding of the river. Caernarvon is not that kind of sediment diversion, it is a freshwater diversion only, designed to lower salinities in an area where saltwater had intruded. Although the water of the Mississippi River contains lots of mud and sand, this diversion project didn’t focus on land-building, and was built instead to provide fresh water to a basin being inundated with salt.
But sitting in the boat, in an area that could no longer be referred to as a sea but rather a sea of plants, we were stunned at what the river had wrought. “This is more than I ever expected,” said John Lopez, a seasoned wetland scientist and executive director of the Lake Pontchartrain Basin Foundation. “This is phenomenal.”
David Muth, the National Wildlife Federation’s Louisiana state director, reached into the shallow water and grabbed a handful from the bottom. “It is mixed sand and silt. Once these plants become established, this marsh will not be washing away in the next hurricane, the way nearby organic soils did in Katrina. This is solid ground.”
So even though the design and intention of this particular diversion hadn’t encouraged it to, the Mississippi River had done what it does – build land. Caernarvon was opened in 1990 and over the years, it’s transported and deposited sand and mud into Big Mar, a little at a time, year after year.
Small areas of land began emerging after Hurricane Katrina. Big flood years on the river in spring 2008 and 2010 provided extra amounts of sediment, and the extended opening of the diversion during the oil spill a year ago might have contributed additional sediment as well, so that when the water receded, more land emerged. And in south Louisiana, it doesn’t take long for plants to take root, grow, and enhance land-building by trapping and holding even more sediment. The spring and summer of 2011 did the trick, and what looked promising a year ago looked spectacular today.
Our boat captains and Chris Macaluso of the Louisiana Wildlife Federation, NWF’s state affiliate, pointed to seed heads on the marshy plants that will feed flocks of ducks in the near future. A few blue-winged teal and mottled ducks served as tantalizing harbingers of the hundreds to follow.
On some of the higher areas, small trees demonstrated the progression of vegetation and habitats that can be expected as land continues to build and emerge from the water. David Muth probed the muddy bottom with a measuring pole to determine water depths–6 inches, 12 inches, 6 inches–in an area originally several feet deep. It won’t be many more years before we can expect those shallow areas to fill and even more land to emerge. Check out comparison photos in this Lake Pontchartrain Basin Foundation report (PDF).
The National Wildlife Federation is committed to restoring a sustainable coast in Louisiana, and the capacity of the Mississippi River to transport sand and build land is a powerful tool. Our trip to Caernarvon provided a first-hand re-affirmation, once again, of this power. At Caernarvon, we didn’t particularly help the river–and it took a long time–but it is doing what the river does – transporting and depositing sand, and building land.
Imagine what a diversion can do that is built to enhance this capacity? We are now capable of marsh-building diversions, that focus on capturing high concentrations of sediment.
So enough about “Caernarvon doesn’t work.” Caernarvon is showing us that the Mississippi River builds land. It always has, and it always will.