On a typical day, when its stilling basin sounds like Victoria Falls and the country that lies between it and the Mississippi is green and tranquil, the Old River Control Structure performs its role seamlessly. But during a sustained period of spring high water in 1973, its capacity was overwhelmed.
The Mississippi is determined to continue flowing towards its final destination of the Gulf. But its journey will take much longer than initially anticipated.
Flooding
At average flow rates, the Mississippi River and its tributaries naturally pass through a back swamp and deposit sediment, helping create unique wetland habitats on which oysters and other aquatic species depend for sustenance. Furthermore, this process builds two deltas in Atchafalaya Bay, providing flood control, water filtering, and wildlife habitat valued at billions each year.
Hydrologic manipulations over decades have caused river flow to diverge away from its floodplain, increasing river speed and straightness while restricting natural backswamp overflow. As a result, water quality and forest health both declined.
Under extreme flooding conditions, releases from Morganza Spillway flood not only the Morganza Floodway and Atchafalaya Basin but many additional areas throughout southern Louisiana. The source of this water comes from higher than usual flows through both Old River Control Structure (ORCS) and Morganza’s auxiliary spillway, as well as flooding due to the high Mississippi River near Baton Rouge levels.
Paddlers planning a journey along the Atchafalaya should consult the Simmesport gauge to gauge water conditions, keeping in mind that even at lower flood stages, navigation channels are impeded by dense forests filled with snags, strainers, sawyers, and other hazards. While wildlife viewing opportunities abound here, paddlers should remember most campsites and landings may be underwater as fast currents create strong whirlpools and boil with strong currents and strong eddies that could make hazardous whirlpools / Boils/currents/sedimendidies/etc.
Dredging
Dredging is a widespread practice in cities, rivers, and harbors around the world. Each year, billions of cubic yards of sediment are removed in order to keep ports and waterways accessible for large shipping vessels. While dredging can be effective at keeping ports and waterways clear for business activities such as shipping vessels passing through them, its benefits also come with drawbacks.
Sucked up by dredges is sediment that may contain pollutants and debris that poses problems to ecosystems in its locality. Furthermore, fossil fuels are frequently used to power these machines’ motors, contributing to climate change; as such, there has been a worldwide movement to limit our dependence on them in general.
Dredging can also rob delta environments of essential sediment for development. This is an issue in the Atchafalaya River Basin where USACE maintenance dredging of the Lower Atchafalaya River Navigation Channel has reduced flow and sediment reaching the Gulf of Mexico; as a result, Wax Lake Outlet and Lower Atchafalaya River deltas only receive three quarters of their required flow and sediment to support growth.
On a smaller scale, dredging can also help clean up contaminated waterways by clearing away trash, sludge, decaying vegetation, and other materials that pollute it. This helps preserve wildlife habitat while solving issues like eutrophication that cause oxygen deprivation in waters.
Dams
Atchafalaya River Basin is Louisiana’s largest river swamp, an invaluable natural resource with fresh marsh, bottomland hardwood forests, and cypress-tupelo swamps. This rich ecosystem serves as a habitat for wildlife and waterfowl while also offering flood relief, navigation channels, and the country’s premier sugar cane crop production facility. Furthermore, this rich resource employs an abundance of diverse people who make a living from this part of Louisiana’s geography.
Flow and sediment resources are fundamental to wetland loss or gain. Natural processes eroding and depositing sediments determine the shape of deltas in Atchafalaya Bay, shaping wetland habitats while providing nutrients essential for commercial fisheries. Human activities and the MR&T project may limit these natural processes by altering flow patterns or decreasing sediment availability for delta buildings.
Before the MR&T project was constructed, during times of sustained spring high water, something extraordinary occurred: Middle America’s drainage passed through Old River Control Structure at rates exceeding two million cubic feet per second for several weeks on end, with 30% going directly into Atchafalaya Bay.
Today, the Army Corps dredged the Lower Atchafalaya River Navigation Channel to ensure an efficient path towards the Gulf of Mexico and to reduce sediment input into Atchafalaya Bay, thus denying its delta environments access to crucial material they require to rebuild themselves. TNC is working closely with partners in order to advance the latest scientific findings in the region as well as devise strategies that increase sediment delivery to Atchafalaya Bay.
Levees
Louisiana’s Mississippi River levee system serves as the foundation of its southern coast, yet its effectiveness cannot be taken for granted. Under certain extreme flood events, water exceeding standard flood control capabilities of Old River Control Structure (ORCS), its adjacent Old River Control Auxiliary Structure (ORCAS), and any flooding from Morganza Spillway releases may overwhelm their capacity and inundate vast portions of Atchafalaya Basin.
Near the ORCS was a large logjam that prevented Atchafalaya’s passage. El Camino Real from Texas passed by it; cattle being driven to market crossed it on their journeys; logs had been put there by workers working on the levee system, creating an ever-expanding blockage raft that had been growing for years.
Rabalais worked as a levee inspector and spent most of his time at ORCS, watching how the Mississippi River and its tributaries behaved.
When the river would shift course again, he’d call upon men from his company to come work on the levees. From dawn till dusk, they worked hard on these levees; once sundown arrived, they returned for more work on these levees; repeated labor, long hours, and daily fears of flood and potential collapse were tedious and took their toll.
