DESCRIPTION OF THE MDPR 



The study area is the seaward por- 

 tion of the deltaic system that was pro- 

 duced from the coastal deposition of 

 sediments by the Mississippi River dur- 

 ing the last 7,000 years since worldwide 

 sea level rose to about its present 

 level. The boundary of the MDPR, as 

 defined for this study, is shown in 

 Figure 2 as comprising seven hydrologic 

 units: I. Mississippi Sound, II. Pont- 

 chartrain, III. Mississippi River Delta, 

 IV. Barataria, V. Terrebonne, VI. Atcha- 

 falaya, and VII. Vermilion. 



area shown in Figure 3: the lower del- 

 taic plain fringing the coast; the 

 active deltaic plain, limited to the 

 leveed flood plains of the Mississippi 

 and Atchafalaya Rivers; the abandoned 

 deltaic plain, which includes a large 

 portion of the alluvial valley of the 

 Mississippi; and the subaqueous delta, 

 some of which was formerly above water 

 and some of which is presently forming. 

 The complete Recent delta extends inland 

 to the Pleistocene Terrace, an ancient 

 shoreline. The MDPR study area is thus 

 limited to about two-thirds of the total 

 deltaic plain in Louisiana, while the 

 Mississippi portion of the MDPR is 

 actually outside the deltaic plain. 



The study area extends from the 

 western side of Vermilion Bay in Lou- 

 isiana to the Mississippi-Alabama state 

 line. The inland boundary is the offi- 

 cial Coastal Zone Boundary in Louisiana 

 as defined in the State and Local 

 Coastal Resources Management Act of 1978 

 and by the 15-ft contour line in Mis- 

 sissippi. The offshore boundary is the 

 three-mile limit. 



The MDPR includes the largest ac- 

 tive delta system, the most productive 

 inshore and nearshore fishery areas, one 

 of the largest concentrations of oil and 

 natural gas, and one of the most active 

 port systems in North America (the New 

 Orleans-Baton Rouge corridor of the 

 Mississippi River) . It also includes 

 the largest contiguous area of coastal 

 wetlands in the country. Forty percent 

 of the coastal wetlands in the United 

 States are in the Mississippi Deltaic 

 Plain and the Chenier Plain to the west, 

 with the largest portion in the former 

 (Gosselink et al . 1979). The wetland 

 habitats in this broad region are 

 changing to open water at a rapid rate, 

 and most of this change has occurred 

 within the MDPR. The region's geologi- 

 cally dynamic nature, acknowledged bio- 

 logical productivity, intense economic 

 activity, and vulnerability to human 

 impacts create a challenge to resource 

 managers . 



The Holocene, or Recent Deltaic 

 Plain of the Mississippi River, as de- 

 fined by geomorphologists, includes the 



THE PHYSICAL SETTING 



The present extent of the MDPR is 

 the result of the physical and biologi- 

 cal processes that have acted upon it 

 throughout its history, processes that 

 include interacting geological, hydro- 

 logical, and climatological forces. 



Geology 



Geologically, the MDPR is a large, 

 crescent-shaped, thick lobe of silts and 

 sands derived from the drainage basin of 

 the Mississippi River system, which 

 includes about 40% of the area of the 

 lower 48 States. The single most impor- 

 tant geologic influence throughout the 

 MDPR is the Mississippi River, which has 

 supplied the sediment to sustain the 

 region in an approximate balance between 

 erosion and accretion. The entire region 

 is composed of fine-grained sedimentary 

 deposits, and these deposits are pro- 

 gressively thicker in a seaward direc- 

 tion. 



The Recent geologic development of 

 the MDPR occurred during the period of 

 rising sea level following the Pleisto- 

 cene epoch. There is disagreement about 

 the time at which the sea level began 

 rising, and when its rate of increase 

 declined, but one estimate is illus- 

 trated in Figure 4. 



Sea level worldwide rose rapidly, 

 beginning about 18,000 years ago, after 



