Louisiana coast will be underwater by 2100

Researchers have concluded that large parts of the Louisiana coastline will be underwater by the end of the century, due to a combination of rising sea levels and shifting sediment levels in the Mississippi delta caused by dam construction.

The study, published yesterday in the journal Nature Geoscience, finds that the amount of sediment in the Mississippi river delta that feeds into the Gulf of Mexico has dropped by half, due in part to the construction of dams in the area. The report predicts that as water levels rise, the reduced sediment levels will be insufficient to build up the flood plain and keep it above sea level.

Authors Michael D Blum and Harry Roberts revealed that an area the size of Connecticut will be lost to the sea, and that there is little if anything to prevent the area becoming inundated.

Even if sediment loads are restored to pre-dam levels, the study, called Drowning of the Mississippi Delta, concludes that rapid sea level rises will mean that the loss of the land is now inevitable.

"Previous projections of twentieth-century land-loss trends suggest submergence of 5,700 km2 of the delta plain between 1950 and 2050," said the study. However, its own figures suggest that these projections are underestimates. About 7,000km2 of the delta plain already lies below sea level, and it says that an extra 10,500 to 13,500km2 will be underwater by the year 2100.

"In the absence of sediment input, land surfaces that are now below one metre in elevation will be converted to open water or marsh," it concluded.

The report will raise further questions about the viability of many settlements in the area and the increased risk of storm surges and hurricanes along the gulf coast, such as Hurricane Katrina's devastation of New Orleans in 2005.

Earlier this year, a new study from climate scientists concluded that previous warnings about sea level rises had been badly underplayed. It found that, based on current rates of warming and sea level rises, the world is on track for a one metre rise in sea levels by 2100 – a scenario that would put one in 10 people globally at risk from coastal floods.