Buttressed by a seven-year respite from major hurricanes, Louisiana’s fragile coast has added an average of more than two football fields of land per hour since 2008, according to the first official government analysis of coastal land loss since 2011.
The highly anticipated report from the U.S. Geological Survey, released Wednesday, updates data that had only been available through late 2010 and includes land area measurements into early 2016.
The USGS 2011 report helped drive home the foreboding message that Louisiana was losing an average of a football field of land per hour. That was based on the average rate of land loss from 1985 to 2010 when sea-level rise and subsidence combined to destroy more than 300 square miles of coastal wetlands.
But even seven years ago, the USGS was already noting that the worst period of land loss from the 1970s was slowing significantly. The 2011 report noted signs of land being added after late 2008 when the state’s total coastal land area appeared to bottom out during the storm surge from Hurricanes Gustav and Ike. Those twin storms battered the coast just three years after the catastrophic flooding and marsh destruction from Hurricanes Katrina and Rita.
From late 2008 to early 2016, the USGS measured a net gain of almost 230 square miles across the whole Louisiana coast, meaning the state actually added a little more than 2 football fields an hour over that relatively short timeframe.
But USGS geographer Brady Couvillion warns in the report released Wednesday that the measurements are still within the margin-of-error and may not be indicative of any long-term trend. The improvements barely make a dent in the state’s disturbing trend of land loss over the last 85 years.
Louisiana has lost a net area of almost 1,800 square miles since measurements began in 1932 – an area one-and-a-half times the size of Rhode Island.
And if the land gains from 2008 to 2010 are considered as basic recovery from the effects of the 2005 and 2008 storms, the improvement over the last six years is modest – only about 17 square miles added.
“The lack of a major hurricane strike since 2008 is probably the main reason we’ve seen a decrease in the rate of land loss,” said Couvillion, who was also the lead author on the 2011 report. “Although ongoing government and private efforts to conserve the state’s coastal wetlands are also a contributing factor.”
Others, including scientists at LSU, have taken the opposite tack, crediting hurricanes with adding to the freshwater flooding that can help build up sediment in coastal marshes. A 2015 article in the journal Water by LSU's Thomas Bianchette found 2012's Hurricane Isaac, which caused major flooding but not much storm surge from the Gulf of Mexico, improved the rate of accretion, or accumulation, of wetlands.
The new USGS report has been delayed for months and its measurements stop in the beginning of 2016, before two major freshwater flooding events in March and August. That's why geologist Chris McLindon, who has worked most of his career in the oil and gas industry, says there's no reason to temper the good news in the latest data.
"To me the storm argument makes no sense," McLindon said. "Storms are the major engines of getting sediment back onto the marsh, which is driving accretion."
Six of the state’s nine coastal basins gained land area since the last report. The three that still suffered a net loss were the Mermentau Basin in southwest Louisiana, the Mississippi River Delta Basin in Plaquemines Parish and, notably, the Atchafalaya Basin in coastal Acadiana, which had been the lone bright spot during the decades of persistent land loss.
The Atchafalaya River, largely unfettered by levees and floodwalls that have hindered sediment distribution along the Mississippi River, has helped that region build more land than it’s lost since 1932. But the Atchafalaya Basin suddenly shrunk in observed size after hitting a peak at the end of 2013, according to the latest USGS data.