O 



(J 



I 

 I- 

 a. 



a 



1000 



2000 



3000 



4000 



5000 



6000 



7000 



C AGE (YEARS B.P.) 



Figure 7. Inferred relative sea-level rise at the Caminada coast of 

 Lafourche Parish (Gerdes 1982). The curve is based on radiocarbon- 

 dated basal peats and in situ, articulated shells of Crassostrea virqinica . 



from local tide gauges, an observation which has two alternative interpretations: (a) 

 natural processes of subsidence in coastal Louisiana are highly tinne dependent, or (b) the 

 rapid subsidence over the last few decades is largely man-induced. Whichever cause is 

 the dominant, however, neither is likely to alter the current subsidence rate dramatically 

 over the next 40 years. A linear extrapolation of current subsidence rates would predict 

 a cumulative subsidence over the next 40 years of 36 cm for the Grand Isle area and 29 

 cm at Eugene Island. The numbers are high; however, both are less than the predicted 

 eustatic rise (40 cm) for the same period. Table I summarizes the predicted amounts of 

 eustatic rise, subsidence, and local relative sea-level rise for the Louisiana coast over 

 the next 40 and 1 00 years. 



Table I. Predicted future changes in sea level on the Louisiana coast based on data from 

 Bayou Rigaud (Grand Isle) and Eugene Island (Atchafalaya Bay). 



Year 



2020 

 2080 



Eustatic 

 rise (cm) 



40 

 60 



Subsidence 

 (cm) 



29-36 

 73-90 



Local relative 

 sea-level rise (cm) 



69-76 

 133-150 



172 



