Do Bigger Diversions Mean Bigger Results?

Imagine wetlands reappearing by hundreds of acres. Imagine oyster production multiplying by millions of pounds. Imagine one of Louisiana's hottest sport-fishing sites developing in your backyard. Now focus on the Caernarvon Freshwater Diversion Project, where all of this is actually happening.

Due to increased freshwater and sediment flow through the diversion, in Caernarvon's 50-year project-span the diversion will protect more than 16,000 acres of wetlands and more than double oyster production on public grounds.

Achieving substantial results like Caernarvon's depends on a proper mix of nutrients and sediment in the diverted river water. Ailing wetlands need these basic building blocks if they are to recover from saline conditions. The influx of fresh water lowers saline levels and allows the return of saline-intolerant plants, such as bulltongue and wax myrtle. Nutrients feed the plants, which in turn hold the sediment together. Over time, plants and sediment form new land.

How Does It Work?

Constructed by the Army Corps of Engineers, Caernarvon reintroduces fresh water into the Breton Sound Basin via five 15-square-foot box culverts that are capable of diverting up to 8,000 cubic feet per second (cfs) from the Mississippi. The culverts are regulated by cast iron sluice gates, which usually open to divert water from December through February.

As with any large-scale project in coastal Louisiana, not everyone embraces freshwater diversions. Perhaps the most controversial issue surrounding Caernarvon has been its short-term effects on oyster beds. When Caernarvon initially released fresh water into the surrounding wetlands, oyster beds farthest inland suffered from the change in salinity levels. Those beds lost most of their productivity, and many had to be moved farther from the river.

Overall, however, long-term results of this pre-Breaux Act project have been positive. Oyster harvests have rebounded, including an almost 90 percent increase since 1992 in St. Bernard Parish. The wetlands are flourishing and returning to salinity levels normal for inland marshes.

The Future

Caernarvon's success offers encouragement to those anticipating more freshwater diversions along the Mississippi. Engineers and scientists are able to study Caernarvon and develop plans to decrease short-term negative results. Caernarvon has also proved that larger projects do produce larger results. Smaller restoration projects have replenished pieces of wetlands all over Louisiana, but none has had the impact of Caernarvon. Because of the possibility for monumental success, diversions may serve to be the backbone of future restoration plans.