Sea-Level Rise and Subsidence: Implications for Flooding in New Orleans, Louisiana

Global sea-level rise is projected to accelerate two-to four-fold during the next century, increasing storm surge and shoreline retreat along low-lying, unconsolidated coastal margins. The Mississippi River Deltaic Plain in southeastern Louisiana is particularly vulnerable to erosion and inundation due to the rapid deterioration of coastal barriers combined with relatively high rates of land subsidence. Land-surface altitude data collected in the leveed areas of the New Orleans metropolitan region during five survey epochs between 1951 and 1995 indicated mean annual subsidence of 5 millimeters per year. Preliminary results of other studies detecting the regional movement of the north-central Gulf Coast indicate that the rate may be as much as 1 centimeter per year. Considering the rate of subsidence and the mid-range estimate of sea-level rise during the next 100 years (480 millimeters), the areas of New Orleans and vicinity that are presently 1.5 to 3 meters below mean sea level will likely be 2.5 to 4.0 meters or more below mean sea level by 2100.