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The Bridge Broken by Katrina, Reborn as a Habitat-Boosting Fish Highway

After a summer of commemoration and ten-year-anniversary reports, South Louisiana residents may be ready to put the incomparable damage wrought by Hurricane Katrina behind them. Coincidentally, though they may not have known it, Louisiana anglers hooking into redfish and bass on the shorelines of Lake Borgne have had the repurposed remains of Katrina’s destruction under them.

The iconic concrete Interstate 10 Twin Span that connected Slidell to New Orleans East was pummeled into a crumbling and collapsing mess by Katrina, and eventually the old structure was replaced with the wider, taller bridge many thousands of Twin Span commuters travel on today. Fortunately, Louisiana’s coastal restoration advocates and agencies and the state office of transportation and development found treasure in what Katrina had trashed. Instead of sending the old concrete to a landfill or pulverizing it for road beds, forward-thinking state officials, conservation groups, and anglers hatched a plan to break up the rubble and use it to build reefs and protect critical habitat.

Since 2011, three reefs—including one named after Lake Pontchartrain legends Dudley and Kim Vandenborre—have been built within sight of the new Twin Span using brick-sized chunks of the old bridge. The bulk of the bridge-that-was, however, has been deposited farther to the east on the Orleans Landbridge, a critical landmass that separates Lake Pontchartrain from Lake Borgne and contains some of the most productive habitat for redfish, speckled trout, and waterfowl in the state.

Image courtesy of Chris Macaluso.

Image courtesy of Chris Macaluso.

An estimated eight feet of shoreline had been lost from the landbridge each year for the last several decades, according to the Louisiana Coastal Protection and Restoration Authority (CPRA) and the United States Geological Survey. Erosion and saltwater intrusion created by the man-made shipping channels of the Mississippi River Gulf Outlet and the Intracoastal Waterway, combined with natural subsidence and wave action, have eaten away at the western edge of Lake Borgne, making a once-healthy swamp and marsh more porous and fractured by the year. Katrina’s pounding also carved away thousands of acres of marshes and shoreline, making an already imperiled habitat even more damage prone.

So, CPRA prescribed a heaping dose of shoreline protection and marsh creation projects to help halt Lake Borgne’s encroachment into the landbridge and preserve the unique fresh-saltwater mix essential to Lake Pontchartrain’s production. Usually these projects would require bringing pumpkin-to-compact-car-sized limestone chunks, cut from mountains in Kentucky and Ohio, down the Mississippi River.

State and parish officials instead saw an opportunity to save costs by creatively using Twin Span concrete from 10 miles away, rather than rocks removed nearly 1000 miles away.

Nearly 220 tons of concrete chunks were broken off of the 1200 spans and pilings removed from Lake Pontchartrain. Those chunks were woven into bags of geo-textile fabric mesh to form mattresses laid along eight miles of Lake Borgne’s shoreline between Bayou Bienvue and Alligator Point. Rather than simply forming a rock line dividing land from water, the mattresses were only half-submerged, forming a new shoreline better able to withstand wave action that gets past traditional rock bulkheads and continues to erode the shoreline.

In addition to stabilizing the shoreline, slowing saltwater intrusion, and helping to foster the return of submerged vegetation necessary for fish and ducks, the mattresses themselves have become havens for aggressive redfish and shorebirds patrolling for minnows and finger mullet. And by using the Twin Span concrete rather than barged-in limestone, CPRA and Orleans Parish saved nearly $11 million on a $31-million effort funded with offshore oil and gas revenues from the Coastal Impact Assistance Program. Construction was completed in 2014.

This July and August, the clear water covering the mattresses allowed anglers to see swarms of mullet and other baitfish congregating and feeding on algae. Redfish and bass staged in the seams where two mattresses meet and along the ends of the mats to ambush the ample mullet and menhaden. Schools of redfish also patrolled in the gaps between mats, left open to allow tidal flow in and out of natural bayous and sloughs, picking off stragglers from the scores of mullet in the area.

Katrina’s damage is still apparent in most places where she carved a path. But her cruelty strengthened the will of Louisianans to become stronger and more resourceful. While the storm may have ended the old Twin Span’s usefulness as a car carrier, Louisiana’s resourcefulness in her wake ensured that she did not make the old, iconic bridge useless.

Creative restoration solutions are still needed all over the Gulf Coast, and the region’s voters are supportive of using BP oil spill fines to get the work done. For more information, click here.

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