margin of the old lagoon, which had become fixed at the steep seaward face of 

 mid-Wisconsinan (?) or Sangamonian coastal barriers. During the past 5,000 or 

 6,000 years, the shoreface has retreated continuously by about 2 km. 



Evidence from southern Long Island and elsewhere in regions of coastal 

 submergence indicates that rapid sea- level rise and low sand supply seem to 

 favor the stepwise retreat of barriers, whereas slow rates of submergence and 

 a greater supply of sand generally favor continuous shoreface retreat. Sta- 

 tionary upbuilding, or seaward progradation of barriers may occur when supply 

 of sand is great, and/or submergence is slowed or reversed. Morphologic highs 

 on the pretransgression surface (such as old barrier ridges) tend to fix the 

 migrating barrier shoreline during either continuous retreat, or stepwise re- 

 treat of barriers. (Authors). 



286 RAMSEY, K. E., MOSLOW, T. F., and PENLAND, S. 1985. "Sea-Level Rise 

 and Subsidence in Coastal Louisiana," In Association of State Floodplain 

 Managers. 9th Meeting . 



The major impact of relative sea-level (RSL) in Louisiana is: 1) land 

 loss within the wetlands and marshes and 2) erosion of beaches and barrier 

 islands along the shoreline. However, the exact role sea- level rise plays in 

 the nature and severity of land loss and coastal erosion remains unresolved. 

 This question is most important to wetland managers and coastal planners in 

 assessing the future existence of southern Louisiana's coastal zone. 



A number of depositional environments are represented within the 26 mil- 

 lion sq. km of coastal wetlands in southern Louisiana. The most common envi- 

 ronments are the coastal marshes which account for 40% of all coastal wetlands 

 in the United States (Gosselink, 1980; Davis, 1983). The coastal wetlands are 

 flat, low lying areas with average elevations of less than 1 m and are being 

 converted to open water bays or lagoons at a progressive geometric rate ex- 

 ceeding 101 sq. km per year (Gagliano et al , 1981). Louisiana faces the most 

 critical barrier shoreline erosion problem in the United States due to rela- 

 tive sea- level rise upon which storms and man's activities are superimposed 

 accelerating the problem (Penland and Boyd 1982). (Introduction). 



287 RAMSEY, K.E., and MOSLOW, T.F. 1987. "A Numerical Analysis of 

 Subsidence and Sea-Level Rise in Louisiana," Proceedings of Coastal 

 Sediments '87 . Vol 2, pp 1673. 



An analysis of historical water level records from 78 tide gage stations 

 and 550 km of geodetic leveling data has documented the spatial and temporal 

 variations in the recent history (1942-1982) of relative sea-level rise and 

 compactional subsidence in coastal Louisiana. Yearly means for the rate of 

 relative sea-level rise were calculated for tide gage stations with continuous 

 daily records from 1942 to 1982. An average rate for the entire statewide 

 region of 0.85 cm/year was determined. For the same time period, this 

 regional rate is 3.7 times greater than the assumed Gulf of Mexico eustatic 

 sea- level rise rate of 0.23 cm/year, and 5.7 times greater than the estimated 

 observed global rise rate of 0.15 cm/year. Statewide sea- level rise rates 

 were calculated at 0.45 cm/year during 1942-1962, and 1.12 cm/year during 



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