Office of Conservation

CAERNARVON PROJECT GIVEN AN "A" BY COASTAL SPECIALISTS

After five years in operations, coastal specialists who have routinely examined and monitored the Caernarvon freshwater diversion project are confident of its success. The project diverts freshwater, nutrients, and sediment from the Mississippi River into the Breton Sound estuary in order to restore the ecological balance that was lost when the area was cut off from the river by flood control levees. "The high rate of marsh healing indicates that our efforts at Caernarvon can be graded above average," reported the state's Coastal Restoration Administrator Dr. Bill Good.

The Breton Sound estuary encompasses 676,400 acres in southeast Louisiana, and has lost over 45,000 acres of marsh since 1932. It is bordered on the east by the south bank of the Mississippi River Gulf Outlet and on the west by the east bank of the Mississippi River. The basin includes portions of Plaquemines and St. Bernard parishes. "The location was right for this type of coastal restoration project and in this case was a practical solution to marsh loss," Good said.

The Caernarvon freshwater diversion project, located about 10 miles southeast of New Orleans, was completed by the U.S. Army Corps of Engineers in 1991. The state sponsor of the project is the Department of Natural Resources. DNR Secretary Jack Caldwell said the most significant factor from the latest Caernarvon statistics is that the marsh has increased in sampled areas at an annual average rate of 5.9%. Caldwell said, "the Caernarvon Diversion is clearly a boon to the people of the area, the state, and the nation. Without marsh, our fisheries would die and our coastal communities would face greater risk from hurricanes."

While the Caernarvon freshwater diversion structure took three years to build, Caernarvon has enhanced emergent marsh vegetation growth, reduced marsh loss, and increased important commercial and recreational fisheries. Wildlife productivity in the Breton Sound estuary has increased, particularly in the number of waterfowl and the number of alligator nests. The structure consists of five 15 x 15 foot gated culverts and, at maximum discharge, is capable of delivering freshwater into Breton Sound at a rate of 8,000 cubic feet per second. Caernarvon cost $25,900,000 to build. The project was funded by the Water Resources Development Act and has a minimum life of 50 years. During its lifetime, the U.S. Army Corps of Engineers estimates that it will yield over $9 million per year in benefits on average.

Since 1988, a rigorous monitoring process by DNR's coastal restoration staff has shown that Caernarvon has lived up to the goals set at the beginning stage. Monitoring data shows that freshwater marsh plants increased over seven times and brackish marsh plants increased by almost half since operation of the structure began; the amount of salt marsh vegetation has decreased by more than half. Caernarvon has actually restored lost marsh, as well. Results show a net increase in marshland of 406 acres within the sampled area which originally contained 2,289 acres of marsh. This comparison represents a three-year period of operation from 1992 through 1994, which translates to an annual increase of 5.9% per year.

Since operation of the structure, oyster productivity in the public oyster seed grounds, a key link in the viability of the state's oyster industry, has increased over three orders of magnitude, and the average number of largemouth bass (Micropterus salmoides) caught has almost doubled.

There has been no fish kills or algal blooms detected since Caernarvon's start up. Coastal officials believe the Caernarvon project provided a freshwater buffer that may have been responsible for keeping the red tide out of the area in 1996.

Caernarvon is one of many coastal marsh restoration projects currently being implemented in Louisiana's coastal zone.

Editors: For more information on this topic, please contact DNR's CRD Project Manager Chuck Villarrubia or Dr. Bill Good at (504) 342-7308. Information also at website at www.lacoast.gov.