Relative Sea-Level Rise in Louisiana and the Gulf of Mexico: 1908-1988

Abstract

Louisiana is experiencing the most severe wetland loss and barrier island erosion in North America. Rates of land loss exceed 100 square kilometers per year in the Mississippi River delta and chenier plains. Rapid sea-level rise induced by delta-plain subsidence and a deficit of terrigenous wetland sediment are the primary factors driving the rapid deterioration of the Louisiana coastal zone. Within the Mississippi River delta plain, the Houma tide gage documented a relative sea level rise rate of 1.09 crn/yr from 1946 to 1988, based on u.s. Army Corps of Engineers tide gauge records. On the coast, the Eugene Island tide gage documented a slightly higher relative sea level rise rate of 1.19 cm/yr. When other tide gag es in Louisiana with 30-year records or more are compared to the record of the Houma tide gage station, relative sea level appears to rise faster in the Terrebonne Parish area than anywhere else in Louisiana. Representative water level histories from the Chenier plain, Teche basin, Terrebonne delta plain, Barataria basin, Balize delta plain, St. Bernard delta plain, and Pontchartrain basin indicate the regional rates of relative sea level rise decrease to the east and the west from the Terrebonne coastal area. In comparison with other National Ocean Survey tide gage records throughout the U.S. Gulf Coast, Louisiana is experiencing the highest relative sea level rise rate at 1.04 cm/yr for Grand Isle, the rates decrease from 0.63 cm/yr at Galveston, Texas to 0.15 cm/yr at Biloxi, Mississippi. Mean relative sea-level rise in Louisiana is more than five times the Gulf of Mexico average. A comparison of the Grand Island relative sea level rise rate (1.04 cm/yr) with the global relative sea level rise rate (0.12 cm/yr indicates that, on the average, relative sea level is rising 10 times faster in Louisiana than in much of the rest of the world. The rapid rate of relative sea level rise observed in Louisiana can be attributed to subsidence of the Mississippi River delta plain due to sediment compaction. Louisiana directly overlies the entrenched Pleistocene valley of the Mississippi River, which is filled with Holocene deltaic sediments more than 150 m thick.