Sea Level Rise in Louisiana and Gulf of Mexico

Karen Ramsey, Shea Penland

Data from two tide-gage networks in Louisiana and the northern Gulf of Mexico were analyzed to determine local and regional trends in relative sea level rise. The U.S. Army Corps of Engineers (USACE) maintains a network of 83 tide-gage stations throughout coastal Louisiana. Of these, 20 have records for two lunar nodal cycles or more, and some date back to 1933. We used the USACE data set to determine the local and regional character of relative sea level rise in Louisiana. The National Ocean Survey (NOS) maintains nine tide gage stations throughout the northern Gulf of Mexico in Texas, Louisiana, Mississippi, Alabama, and Florida. All of the records of these stations exceed two lunar nodal cycles, and some date back to 1908. We used the NOS data set to determine the char cter of relative sea level rise throughout the northern Gulf of Mexico. This investigation updates and extends the previous systematic regional tide gage analysis (which covered 1908-1983) to 1988.

Based on the USACE data set, the rates of relative sea level rise in Louisiana range from 0.34 cm/year to 1.77 cm/year. Within the Mississippi River delta plain, the Houma tide gage documented an average relative sea level rise rate of 1.31 cm/year for the entire record. On the coast, the Eugene Island tide gage documented a maximum relative sea level rise rate of 1.19 cm/year. Comparing data from other tide-gage stations with records of 30 years or more to the record of the Houma tide-gage station reveals that relative sea level is rising 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 b sin indicate that the regional rates of relative sea level rise decrease to the east and the west from the Terrebonne coastal area. Rates of relative sea level rise in the Teche basin reach a maximum of 1.77 cm/year at Calumet; however, these rates reflect the increasing stages of the Atchafalaya River.

On the basis of records from NOS tide-gage stations throughout the U.S. Gulf Coast, Terrebonne Parish is experiencing the highest relative sea level rise at 1.19 cm/year. In the surrounding coastal states, the rates of relative sea level rise decrease from 0.62 cm/year at Galveston, Texas, to 0.15 cm/year at Biloxi, Mississippi. Mean relative sea level rise in Louisiana is more than five times the average for the Gulf of Mexico. A comparison of the Eugene Island relative sea level rise rate (1.19 cm/year) with the global relative sea level rise rate (0.12 cm/year) reveals that, on an average, relative sea level is rising 10 times faster in Terrebonne Parish than in the rest of the world.

The rapid rate of relative sea level rise observed in Louisiana can be attributed to the compactional subsidence of the Mississippi River delta plain. Louisiana directly overlies the entrenched Pleistocene valley of the Mississippi River, which is filled with Holocene deltaic sediments more than 150 m thick.

AAPG Search and Discovery Article #91029©1989 AAPG GCAGS and GC Section of SEPM Meeting, October 25-27, 1989, Corpus Christi, Texas.