ABSTRACT: Effects of Sea Level Rise on Deltaic Coastal Marshlands, Mississippi River Deltaic Plain

Karen E. Ramsey, Harry H. Roberts, James M. Coleman, Shea Penland

Low-relief deltaic coastal plains commonly experience land loss because of the cumulative effects of natural and human-induced processes. Although it is difficult to separate the individual factors within the overall process, interplay between these factors can result in a rate of relative sea level rise greater than the natural rate of coastal-plain aggradation that causes land loss.

Between 1956 and 1978, about 11,400 and 2490 ha of marsh were lost in east Texas and Mississippi, respectively. Louisiana's loss was 18,755 ha. Relative sea level rise over the last 65 yr has averaged 0.23 cm/yr in the Gulf and as much as 1-1.5 cm/yr in the delta plain.

The Environmental Protection Agency predicts the rate of sea level rise to increase over the next century. Rates of relative sea level rise for the Gulf of Mexico are expected to increase from 0.23-1.5 cm/yr to 0.6-3.7 cm/yr. The current rate of relative sea level rise and land loss in the subsiding Mississippi delta is a response that can be expected for many U.S. coastal areas over the next century. With the predicted change, the Mississippi River delta complex will experience dramatically increased rates of land loss. Isles Dernieres will disappear by the year 2000, and Plaquemines and Terrebonne marshes will be gone between 2020 and 2080. Based on the lowest predicted sea level rise rate, by the year 2100, the delta plain could be reduced from 150.9 × 10³ ha to 29. × 10³ ha or to 4.9 × 10³ ha if calculations are based on the highest rate.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990