A Case Study: Channel Armor Gap Crevasse

When river water scours a crevasse through a levee and spreads over the land, the fresh water, nutrients and sediment rejuvenate the coastal habitat. While crevasses caused by floods have been vital to wetlands, they are also dangerous and destructive. Today, fresh water and sediment can be reintroduced through the levees in a safe and controlled fashion. The Channel Armor Gap Crevasse that allows water from the Mississippi to flow into Mary Bowers Pond is an example of a planned crevasse that is beginning to restore wetlands of the Delta National Wildlife Refuge in the Mississippi River Birdsfoot Delta.

Prior to 1997, Mary Bowers Pond was receiving inadequate fresh water and sediment from the Mississippi. Although some water from the river reached the pond through three openings (an oil company crevasse, and two opened by the Corps of Engineers), the supply was not sufficient. Consequently, the area degenerated into barren mudflats.

Completed in December 1997, the Channel Armor Gap Crevasse widened and deepened one of the existing gaps, allowing a maximum water flow through the crevasse of approximately 2,500 cubic feet per second. By 1999, although new shoals had developed in the area of the crevasse, there was no evidence of emerging land. But in October 2001, field trips to the area revealed that the first small area of land had appeared. The 2001 first post-construction vegetation surveys showed a pioneering plant species, Sagittaria, commonly known as arrowhead, colonizing the emergent land.

Although the addition of sediment from the other two splays makes it difficult to ascertain the proportions contributed from each source, the Channel Armor Gap Crevasse is expected to eventually create 936 acres of freshwater marsh over the 20 years of the project.

Under similar Breaux Act projects, other small crevasse splays are planned. In concert with the large diversions, and equally vital to the goal of restoring sediment and fresh water to Region Two's wetlands, these small, low-cost projects have the potential of creating or restoring an additional 2,400 acres of land by 2020.