For centuries, people have compared the Mississippi to other great rivers like the Nile, Euphrates, Indus, Hoang-Ho (now Yellow River) and Po. At one time or another, each of these great rivers served as the cradle of Egyptian, Assyrian, Hindu, Chinese and Italian civilization.
The Mississippi is North America’s great river; collecting and delivering 406 million tons water annually from across the United States and part of Canada.
Over time, rivers change. They shift their course and flow patterns as they travel from source to sea. Throughout this journey, loose clay, silt, sand, gravel and organic material is collected from riverbanks. As this mixture travels it becomes sediment, which is deposited when the river reaches its final destination.
In the past, humans living near the mighty Mississippi accepted seasonal flooding, river erosion and sedimentation as natural processes. However, attitudes changed in the twentieth century as humans sought control over the river’s seasonal flow with a series of levees and canals.
Despite good intentions, these initiatives had several unintended consequences. Reducing the seasonal ebb and flow of water contributed to the significant loss of prairie wetlands and floodplain forest decreasing the biodiversity of the region. At the same time, sediment was used to fill in and convert land for agricultural use leading to increased run-off of fertilizers and pesticides. In addition, industry located along the river has also been a significant polluter. Together they have had a negative impact on the life and safety of communities and the energy sector infrastructure that is such an integral part of Louisiana’s culture.
Experience pays off
After two hundred years of trying to control the Mississippi, the State of Louisiana has enlisted COWI Marine — global leaders in marine and coastal engineering — to design and implement long term, sustainable solutions that work with, not against, nature.
Currently, COWI is working south of New Orleans in the lower delta of the Mississippi River. Its multifunctional project team creates innovative marine engineering solutions tailored to exceed clients demanding needs and expectations. The team’s vast knowledge and experience designing and constructing large complex hydraulic structures in some of the world’s most demanding maritime conditions including rising sea levels and threatening extreme climate change events such as rivers, floods and hurricanes.
Founded in Denmark 90 years ago, COWI is one of the world’s leading marine, coastal and port engineering firms. It has worked in all the world’s great river deltas. In the past decade, COWI has received many industry awards and accolades and is currently ranked fourth in the world for marine engineering by Engineering News-Record.
Since the 1930s and the onset of industrialization, the US Geological Survey estimates that Louisiana has lost more than 80 percent or 1,883 square miles of wetlands —swamps and marshes —in its coastal areas.
Following Hurricane Katrina (2005), COWI came to Louisiana to bring modern, sustainable expertise and solutions for reestablishing wetlands and restoring the natural resiliency of a complex riverine and coastal environment.
Industrialization has negatively affected rivers around the world. COWI Marine has experience implementing viable long-term solutions to prevent sediment loss in Vietnam’s Mekong River delta. Many of the same COWI team are now using their experience to create long-term viability and sustainability of sediment diversion on the Mississippi.
One climate adaptation of these solutions is the award-winning Inner Harbor Navigation Canal/Lake Borgne Surge Barrier. This project involved experts at COWI evaluating soil-structure-interaction for the placement of a very large marine structure in poorly founded soils. The construction method was “In-the-Wet”, a highly innovative marine construction method that COWI designers established in North America. COWI’s staff have applied this method to dozens of lock and dam projects all along the Mississippi River Valley — currently considered for constructing structures diverting the Mississippi River south of New Orleans.
These natural sediment diversions are intended to rebuild the Louisiana coast with the rich sediments of the Mississippi River by gradually reintroducing them back into the vast Louisiana wetlands, which are the largest within America.
What is sediment diversion? A sediment diversion is a man-made system strategically designed by engineers to reconnect the river to the delta, slowing the river’s flow through the sediment diversion into selected areas.
The future looks bright
Now more than ever, we are aware of the important role southern Louisiana’s wetlands play in helping to temper force of the raging tropical storms and hurricanes that roll across the landscape. However, this knowledge and understanding is still relatively new.
In the eleven years since Hurricane Katrina, government at all levels has come together to make investments to restore and protect the long-term viability of the majestic Mississippi delta.
While change can’t happen overnight, the future looks positive.
Part 2 of this article on sediment diversion will look at some of COWI’s recent sediment diversion efforts on the Mississippi river delta.