Louisiana officials establish formula for anticipating sea-level rise

Mark Schleifstein in the New Orleans Times-Picayune: State coastal restoration and levee projects should be designed to anticipate an average 3.3 feet increase in sea level over the next 100 years, according to a new Coastal Protection and Restoration Authority report. But the project designs must also consider whether changing circumstances, including a reduction in the speed in which coastal land is sinking or a possible catastrophic increase in atmospheric temperatures, could produce sea levels rises of only 1.6 feet or as high as 4.9 feet by 2112.

The report released this week by the Louisiana Applied Coastal Engineering and Science Division (LACES) provides planners with a formula for anticipating the rate of “relative sea level rise” — the combination of the effects of sinking soils and rising water levels — at varying locations along the coast.

Louisiana is unique among the nation’s coastal states in having some of the world’s highest rates of soil subsidence in the footprints of present and past deltas of the Mississippi River that make up the eastern two-thirds of the state’s coastline. Rising water levels are caused by a combination of natural and human-caused warming of the atmosphere, often referred to as climate change.

...The White House Council on Environmental Quality has ordered federal agencies to consider the effects of human-induced climate change in designing longer term federal projects, including the potential effects of “abrupt climate change,” where rising temperatures could cause larger than predicted increases in ice melt, and thus sea level rise.

The majority of proposed coastal restoration and levee projects will be either partly financed with federal money or will require permits from federal agencies. However, the report recommends against using a similar relative sea level rise formula adopted in 2008 by the Army Corps of Engineers because it is too broad-based to deal with the differing sea level rates along the state’s coastline, said Garret Graves, chairman of the authority....

Sand bar adjacent to Pass a Loutre. Possible sediment source for restoration projects. Bar features are natural. Louisiana, Pass a Loutre area. 1994 June 15, shot by NOAA