Hurricane Ida blamed for “insanely large” loss of 106 square miles of wetlands | Environment

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Hurricane Ida could be responsible for the loss of 106 square miles of wetlands, an area barely larger than Baton Rouge, with most of the losses occurring in the Barataria Basin south of New Orleans, announced Wednesday. the Louisiana Coastal Protection and Restoration Authority.

“It’s incredibly important,” said Brady Couvillion, a geographer with the US Geological Survey, of the preliminary estimate. “This is probably the most impactful storm we have seen since Hurricane Katrina, and it is certainly the most impactful event for the Barataria Basin in recorded history.”

But Couvillion warned that total terminal losses are likely to decline, as wetlands recover over the next year.

This graph shows the preliminary estimate of land loss from Hurricane Ida along the Louisiana coast.

AMERICAN GEOLOGICAL SURVEY GRAPHIC

“We saw it with Katrina,” he said of the 2005 storm, which was accused of turning more than 200 square miles of wetlands into open water along the Louisiana coast. “We’ve seen it with Rita, Gustav, Ike. Those initial numbers are often inflated, because they have fleeting effects, and as we continue to observe things, those numbers will go down.”

Yet Wednesday’s estimate, the first to quantify the size of wetlands lost to Ida, highlights the growing vulnerability of southeast Louisiana at a time when climate change is causing more intense storms.

Estimates include the loss of floating agents, a type of wetland grasses that grow mat on the surface of the water and are connected to the bottom of the water by long roots. But they don’t include aquatic plants that simply grow on the surface of the water.

This bar graph shows the estimated amount of land loss in different areas of Southeast Louisiana after Hurricane Ida.

AMERICAN GEOLOGICAL SURVEY GRAPHIC

Couvillion said another part of the estimated totals that is likely to change are areas where some of the floating vegetation, other vegetation or mud redirected by Ida appears as new land. Plant life that is moved into areas of open water, often called wrack, is likely to disappear as it decomposes.

He said scientists have to wait weeks, months or more to make sure the high water levels caused by the storm or other problems don’t mask the amount of land and wetlands actually lost. As an example, he showed a satellite photo of an area of ​​wetlands and floating just south of Lake Salvador. It appeared to have turned into open water on August 30, the day after Category 4 Ida made landfall at Port Fourchon, blowing sustained winds of 140 mph and pushing a storm surge of over 12 feet. in parts of the Barataria Basin.

This satellite image from August 30, 2021, the day after Hurricane Ida passed, mainly shows storm surge floodwaters, rather than permanent land losses, south of Lake Salvador.

AMERICAN GEOLOGICAL SURVEY IMAGE

“There have been a few early reports showing this picture of complete disaster for the entire Barataria basin,” he said. “But that’s an important aspect of the way we study wetlands. We can’t look at a particular day. We knew that it was largely just ephemeral flooding.

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“Instead, we gave it a bit of time and collected more footage, and unfortunately when we started looking at footage that got deleted from the event, we found a lot of lingering loss. wetlands, Couvillon said. He used before and after photos from that same area, with the last photo of Sept. 24, nearly a month after the storm, as an example.

This map shows the estimated height of the storm surge caused by Hurricane Ida.

LSU COASTAL EMERGENCY RISK ASSESSMENT ILLUSTRATION

By this time, it was clear that large areas south of Lake Salvador, east of Delta Farms and Clovelly Farms, and west of Little Lake, had turned into open water.

Coastal Authority Chairman Chip Kline said the location of these lost wetlands was important as they served as a buffer zone for the hurricane breakwater from Larose to Golden Meadow.

BY DAN SWENSON | Graphic editor

Couvillion said he expects a more accurate estimate of Ida’s losses in the results of his agency’s update on Louisiana’s coastal land loss, which will be released in early 2022. But even in this case, future adjustments are likely as more wetlands regain a foothold after the next natural spring growth.

He said the updated report was supposed to have been released this fall, but was delayed to capture Ida’s effects. The report will also address similar land losses that occurred as a result of Hurricanes Laura and Delta in 2020 in western Louisiana, he said.

This map shows the trajectories of major hurricanes, category 3 or greater, that crossed the Louisiana coast between 1852 and 2021.

NATIONAL ILLUSTRATION OF OCEANIC AND ATMOSPHERIC ADMINISTRATION

Couvillion said there was little past research linking major hurricanes and land loss. Most of the previous studies have focused on other known issues, such as subsidence, loss of sediment caused by the Mississippi River dike system, and the construction of canals and shipping channels for oil, gas. and trade.

The coast has lost more than 1,900 square miles of land and wetlands since 1930, he said.

But more recent studies, such as the Geological Survey’s review of wetland losses associated with Katrina in 2005, have indicated that storms are a significant player. As a result, he said, Ida’s damage came as no surprise.

Category 4 storm surge, the waves tore the grass from the swamps and washed them away

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This work is supported by a grant funded by the Walton Family Foundation and administered by the Society of Environmental Journalists.

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