ATCHAFALAYA DELTA: SUBAERIAL DEVELOPMENT 

 ENVIRONMENTAL IMPLICATIONS AND 

 RESOURCE POTENTIAL 



Robert Cunningham 



Center for Wetland Resources, Louisiana State University 

 Baton Rouge, Louisiana 



ABSTRACT 



A major geologic event in the 

 history of the Mississippi delta sys- 

 tem is now in progress along the cen- 

 tral Louisiana coast. Because of a 

 distinct gradient advantage, the main 

 distributary of the Mississippi Riv- 

 er, the Atchafalaya River, is rap- 

 idly developing a subaerial delta in 

 Atchafalaya Bay, 130 miles (200 km.) 

 west of the modern bird-foot delta. 



The subaerial growth of the new 

 delta is being monitored with remote 

 sensing techniques, land and hydro- 

 graphic surveys and a sediment sampl- 

 ing program. Initial formation of 

 new land in the Atchafalaya Delta has 

 been found to occur sporadically with 

 accretional periods coinciding with 

 flood pulses ofl the river. Approxi- 

 mately 12.39 mi (32 km ) of new land 

 had been formed by 1976 with addi- 

 tional accumulations following the 

 1979 flood. 



A prototype data collection pro- 

 gram is currently underway to provide 

 data for a study of estuarine hydro- 

 dynamics and sediment transport in 

 the bays and near offshore areas of 

 the Atchafalaya-Vermilion estuarine 

 complex. Accretional impact lines 



include subaerial deltaic sedimenta- 

 tion, subaqueous bay fill and mud- 

 flat-marsh building in a region for- 

 merly characterized by shoreline re- 

 treat. These impacts are presently 

 producing negative effects on open 

 water habitats, but the potential for 

 improved marsh and aquatic nursery 

 ground environments and expansion of 

 human habitats in the vicinity of 

 Morgan City far outweighs loss of 

 open bay habitats. The Corps of 

 Engineers is considering several pro- 

 ject alternatives for mitigation of 

 present impacts and management of 

 future delta growth. 



INTRODUCTION 



A remarkable new geologic event 

 in the 6,000 year history of the Mis- 

 sissippi delta complex is currently 

 unfolding in Atchafalaya Bay, along 

 the central Louisiana coast near Mor- 

 gan City, Louisiana (Figure 1). Con- 

 struction and abandonment of a major 

 delta lobe of this system occurs on 

 a time scale of about 1,000 years 

 (Kolb and Van Lopik 1966). Since 

 the present 800-year-old bird-foot 

 Balize Delta has prograded far out 

 onto the continental shelf, the 

 Mississippi River has lost much of 

 its efficiency for delivering water 

 and sediment to the gulf. 



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