The first article in this series looked at the evolution of the Mississippi River and the efforts humans have made to try to control the flow of water and sediment into her wetlands and her delta by installing levees and control structures to protect communities, businesses and crops from her force. These efforts have worked but sadly, have had unintended consequences – this includes what national and international experts as the world’s largest land loss crises recognize.
Since the 1930s, the river has been restricted from replenishing the sediment in her delta. The river is nature’s delivery system to replenish and sustain Louisiana’s valuable wetlands, which is naturally subsidized like all great deltas fed by large riverine systems. Sealing the delta off from its source of replenishment has had devastating effects on the people, wildlife and jobs reliant on these wetlands and estuaries. Instead, the wetlands are disappearing at the astonishing rate of 16 square miles of land each year cumulatively reaching roughly 1900 square miles since 1930.
In 2005, Hurricane Katrina overtopped and breached levees and barriers. Natural buffers, such as the marsh that once lay in front of these manmade protection systems, have collapsed due to the constriction of the Mississippi River from her wetlands.
One of the positive outcomes of Katrina was the creation of the Multiple Lines of Defense (MLOD) Strategy. The MLOD Strategy is working with a wide range of partners to build coastal resilience by coordinating coastal restoration with traditional flood protection, such as levees. The first line of defense starts at Louisiana’s barrier islands and associated back barrier marshes. These have experienced an infusion of funded projects previously unseen within the U.S. coastal system.
Since this restoration work began, COWI Marine – global leaders in marine and coastal engineering – has been working closely with MLOD partners on adaptable engineered and natural solutions to improve long-term coastal sustainability and flood protection. Four of these key projects include the Lower- and Mid- Barataria Sediment Diversions and the Lower- and Mid- Breton Sound Sediment Diversions. The current focus is on the two Mid Basin Sediment Diversion projects, to which COWI Marine is bringing knowledge and experience gained on large complex marine construction project from the Mississippi River Valley in South Louisiana.
Mid-Barataria Sediment Diversion
Over the past century, the Mid-Barataria Basin situated within Barataria Bay has some of the highest rates of land loss within coastal Louisiana – over 450 square miles since 1932. As a result, it is more vulnerable to sea level rise, salt-water intrusion and more intense storm surge from tropical events. This will lead to greater force upon the man-made protection systems of levees, barriers and control structures.
In 2007, the need to re-establish a connection between the river and the basin was identified. Using adaptive engineering, COWI Marine reviewed ongoing comprehensive studies of the basin looking at the physical, hydrodynamic and morphological characteristics of the Barataria Basin. These findings informed the location and capacity of the diversions, which will mimic natural processes and maximizing land building. Their purpose is to protect people and infrastructure from future storm event.
COWI’s proposed solution is a highly innovative “In-the-Wet” method, which offers significant improvements to more conventional diversion systems. Water and sediment flow would be managed through adaptive engineered marine structure, designed to be adjustable to seasonal ebbs and flows on the basin side and the river side of the structure. By balancing nature with technology, southern Louisiana achieves the best of both worlds.
While Hurricane Katrina caused a lot of damage — the most costly natural disaster in U.S. history ($80 billion) — it has also initiated a once in a lifetime opportunity to restore southern Louisiana. The Mississippi River may reach greatness once again when reconnected to her delta.
In the final article in this series, learn how COWI’s award-winning innovative design-build of the Inner Harbor Navigation Canal – Lake Borgne Surge Barrier is not only protecting New Orleans but also making it more resilient and adaptable to the environment.