Mapping shoreline activity in Louisiana

by

comment

Volunteers build up a coastline in Plaquemines Parish.
  • Photo courtesy Louisiana Office of Coastal Protection and Restoration
  • Volunteers build up a coastline in Plaquemines Parish.

There’s an adage among geographers that you can’t manage the landscape without measuring it first. That’s true of Louisiana’s coastal wetlands, which bear the brunt of 90 percent of the land loss suffered by the continental U.S.

It was with that in mind that the National Wetlands Research Center in Lafayette produced an unprecedented, multi-layered topography system that not only accurately depicts Louisiana’s coast but also shows 78 years’ worth of shoreline activity. You can download that map here.

The map and data produced by the project were released last week and republished by dozens of print, broadcast and online outlets around the world. Here’s a synopsis of the headlines still being rolled out: The seventh-largest delta on the earth’s surface has experienced a net loss of 1,883 square miles since 1932.

That delta, of course, is Louisiana’s wetlands, which also have experienced a decline in rate of land loss over the past 25 years, due chiefly to renewed interest in public advocacy and taxpayer-funding coastal restoration and protection.

D. Phil Turnipseed, director at the Lafayette center, said the emerging government-led industry that is inventing new forms of engineering to add infrastructure to Louisiana’s coast requires such a map. Among the map’s unique features is its ability to show areas that have lost land since 1932 and explain, for each point in history, why land was lost — whether it was the result of a storm, oil activity, natural subsidence or other factors.

“We believe this map will help the decision makers and the agencies that are strapped with the responsibility of having to look at this loss,” Turnipseed said. “We believe it will be a great restoration tool.”

USGS_Land_Loss_Map.pdf

The significance of the new map is all about timing. Previous studies have analyzed land change in coastal Louisiana, but many are out of date, provide data for limited time periods or fail to explain how and when losses occurred. Under the leadership of Turnipseed, and with the resources of the United States Geological Service (USGS), the map was constructed by more than 150 engineers, programmers and ecologists. Turnipseed described it as a fitting endeavor in the face of such a massive challenge. “This is a continental issue,” he said. “It’s a continental tragedy.”

When the USGS, which oversees the wetlands center, presented the map and related findings to state lawmakers last week, several legislators complimented Turnipseed’s team on its unique methods. To track landscape changes, the project team relied on historical surveys, aerial data, personal interviews, satellite data and more. Others on the Joint Natural Resources Committee asked Turnipseed why he limited his research scope.

“I have a 95-year-old trapper in Larose [who] tells me that the oilfield contributed to the erosion but it started with a four-legged varmint — and not a nutria: the muskrats,” said Rep. Jerry “Truck” Gisclair, D-Larose. “The muskrat was a root-eating varmint. The nutria ate the greens.” Gisclair urged the federal government to begin interviewing other sources, including trappers.

“You hit it right on the head,” USGS geographer Brady Couvillion told Gisclair. “It’s the roots holding onto the soil that help prevent erosion from happening.”

In building the map, the wetlands center extrapolated some new twists to data you’ve probably heard before. Like the fact that today, Louisiana loses one football field worth of land every hour. “There was a time when we were losing a football field every half an hour,” Turnipseed said. “It has declined over the last few years if you take out the fact that we have had four or five of the most severe hurricanes to hit the North American coast.”

That recently adjusted statistic doesn’t take into account those areas that have converted to water but have not yet exhibited the persistence necessary to be classified as a “loss.” Even with the variables, trend analyses by the wetlands center show that from 1985 to 2010 there was a wetland loss rate of 16.57 square miles per year. “If it was a constant rate, we would be losing about the island of Manhattan annually,” Turnipseed said.

Lawmakers last week also viewed slides recounting Louisiana’s historic river levels. While this year’s flood presents challenges, the event is also pushing sediment-rich water into the state’s marshes. This will build up land — the antithesis of coastal erosion.

But there is bad news as well: The sediment doesn’t always go where ecologists and biologists think it should, Turnipseed said. Science and technology help, but Louisiana’s infrastructure isn’t quite ready to accommodate such a flow right now. “It’s unfortunate to see both the land loss rate and the potential that’s being lost,” said Jerome Zeringue of the Governor’s Office of Coastal Activities. “You look at all that sediment that could be used as a positive (to) take advantage of the situation, but we ... don’t have the ability to do that right now.”

Zeringue said, however, the state is working with the U.S. Army Corps of Engineers on a variety of projects that could soon help Louisiana push that valuable sediment into all the right places.

As for the parishes with the most land loss under the survey, Plaquemines leads the way with nearly 1,200 square miles lost over the past 78 years. Terrebonne is right behind with 800 square miles lost since 1932, then Cameron with 600 and Lafourche with nearly 400.

Not surprisingly, the crown jewel of south Louisiana is the Atchafalaya Delta Basin. Always rich with sediment, it’s the only area in coastal Louisiana showing an increase in land mass, but the rate of growth there is not sufficient to offset the losses elsewhere on Louisiana’s coast, particularly in years of increased hurricane activity.

Add a comment