The Mid-Barataria Sediment Diversion
Land loss in the Mississippi River Delta is largely a result of stunted natural processes. To reverse coastal land loss over the long-term, we must restore natural processes to the delta system. River diversions harness the Mississippi's power to deliver sediment, water and nutrients to the delta's wetlands. By reconnecting the river to its delta, they mimic nature to build new land. Used correctly, these diversions are a key tool in restoration planning.
Such is the hope for the proposed mid-Barataria sediment diversion
Now in the design stages, this diversion, located between New Orleans and Barataria Bay, addresses an urgent need for a degraded wetland area. A unique partnership between government and the Mississippi River Delta Restoration Campaign brought in academic researchers and technical consultants who spent countless hours collecting data and modeling the diversion.
To predict this project's land building potential, researchers first sought to understand the river's bottom, water flow and sediment content. The Mississippi River's sediment, the key to rebuilding the delta, consists mostly of fine material. However, in periods of higher flow — when the river rushes at a rate of 700,000 cubic feet per second (cfs) or greater — more of the larger, heavier sand is carried by the river.
Though the delta needs both fine material and heavy sand, this heavy sand offers the most stable base for a marsh platform. This link between river discharge and sand suggests that higher flow diversions best maximize land building by delivering the highest quantity of heavy sediment.
With research in hand, scientists then created a 3-D model to forecast land building within Barataria Bay.
Using flow and sediment data, researchers compared a 15,000 cfs and 45,000 cfs diversion to measure the differences in land building between diversion sizes. Simulating conditions over 25 years, the 45,000 cfs diversion deposited 32 million cubic yards of sand — four times more than the smaller one. This offers a hopeful look at the land building prospects of high-flow diversions. At the same time, actual land building potential could be higher, as the model did not include the effects of vegetation, the presence of which aids land building by trapping clays and fine silts.
The Mississippi River, through waterborne shipping, provides a vital service to our nation's commercial activity, and so though land building is the ultimate goal, planners must also reduce or eliminate adverse effects on the area's navigation channel. To do this, researchers have used the same model of the river to better understand the area's water and sediment flow.
Simulations of three diversion sizes — 15,000cfs, 45,000cfs and 75,000cfs — gauged the ratio of sand-to-water at each flow rate. The results show that larger diversions have higher sand-to-water ratios. This means that more sand is diverted into the wetlands while a higher percentage of water stays in the river channel, serving the dual purposes of maximizing land-building while maintaining the navigation channel.
Towards the Future
Louisianans have traditionally used diversions to reduce water salinity in the delta's basins. Today, diversions present a new set of challenges and require a thorough knowledge of river flow and sediment transport. However, with proper planning, mid-sized diversions like the mid-Barataria project can mimic the natural processes that once created Louisiana and lead the way to a new coastal future.
- Slide show, "Marsh Building Mid-Barataria Diversion" (pdf)
- Louisiana Coastal Area, Background of Mid-Barataria
- Coastal Wetlands Planning Protection and Restoration Act project information
- Delta Dispatches, Mid-Barataria blog posts