The Atchafalaya Basin is a globally unique swamp within the State of Louisiana, a last remnant of an ecoregion that cradled ancient civiliations. The Basin also serves as a floodway for the Mississippi River and Tributary System, as well as a resource for the wild harvest of crawfish. Major modifications by the MR&T project, as well as numerous east-west pipelines subject these swamps to unnatural sources of coarse sand fill, deposited every time the river rises.
We surveyed depth and vegetation on two transects. These sediment plumes are often moving coarse sands over the banks of bayous and levees and into the swamps. This blocks flow, and fills historic bayous. This results in the degradation of deep swamps by providing substrate for invasive vines. The vines remove bird access and roosting habitat. Eventually hardwood trees outcompete Cypress and Tupelo.
The plumes are often aligned with oil transmission pipelines, east-west. The east-west configuration blocks the north-south flow, leading to hypoxic waters which remove the suitability for fish and crawfish. These plumes act as hydraulic dams, aggravating the accretion from other pipeline channels.
Results/Conclusions
The sediment plumes’ impact on forest vegetation and flood regime is visible in the National Wetland Inventory, 1998. Sediment enters PFO2/1F swamp and changes to PFO1/2F from the north. But sediment plumes are most visible in the PFO1/2C designation--the change from semipermanently flooded to seasonally flooded. Survey of sites along two transects confirms the conversion of lakes, bayous and swamp to degraded swamp, then broad-leaved hardwoods, along a transect along Lake Zadrick into Salt Mine Bayou in the East Grand Lake District.
Within management areas, the Atchafalaya Basin is comprised of all of these types, currently filling in from “F” to “C” in 225183 acres of 502767 total acres, leaving 256091 acres of semipermanently flooded forest to remain. The plumes are most visible as PFO1/2C-- 64528 acres.
We were also witness to the rapid movement of a sediment plume into Lake Zadrick. Using an aerial photo series, we note the growth of the plume at roughly one half acre per year.
These sediment plumes represent a lost opportunity for coastal restoration, as the plumes rob sand from river channels building marsh deltas to the south. We present this study in the hopes of discussing a modelling effort to measure how much additional sand is lost to the coast by filling river swamps.