( V 





STUDY AREA 



HYDDOLOGK UNIT BOuNIIARIE; 



. , fT^no,,:,... I PONTCHARTRAINj 



h^, \ lA ^4; '-^ 



j^RR^BO^Nrft^^.J S 



G(/tF OF MEXICO 



Figure 5. Map of the Mississippi River Deltaic Plain showing the hydrologic units, 



al. 1983). These data and maps are from 

 a recent Fish and Wildlife Service study 

 of the Mississippi Delta Plain Region 

 (Wicker 1980; Wicker et al. 1980a, 1980b). 

 The drainage basins are interdistributary 

 basins formed by shifts in the major 

 distributary of the river. Thus they 

 forni a time series of delta lobes of 

 different ages and allow one to see in 

 space the time sequence of the development 

 and decay of the marshes of a delta lobe. 



The active Mississipoi River delta, 

 the Balize Delta, is next youngest. It 

 receives two-thirds of the flow of the 

 Mississippi River, but it is debouching 

 into deep water at the edge of the 

 continental shelf. Most of this basin is 

 fresh also, but there has been marine 

 invasion of abandoned 

 around the edges 

 distributaries, and the 

 brackish. 



subdelta lobes 

 of the main 

 marshes here are 



The youngest basin is the 

 Atchafalaya, which is actively prograding 

 out through the shallow Atchafalaya Bay. 

 It receives one-third of the flow of the 

 combined Mississippi and Red river 

 systems, whose freshwater flows into the 

 shallow bay keep the whole basin 

 fresh or nearly fresh all year. All the 

 marshes in this basin are fresh. 



In succession Barataria, Terrebonne, 

 Vermilion-Cote Blanche, and the 



Pontchartrain-Lake Borgne basins are of 

 increasing age. They all have extensive 

 marshes with well-developed salt and 

 brackish zones. These six basins 



together form the Mississippi Delta Plain 

 Region, one of the best-developed deltas 

 in the world. The Mississippi Delta Plain 

 Region is also the largest continuous 



