From Satellite Imagery to Soil Samples
Scientists Take the Pulse of a Pummeled Coast
Marsh vegetation brown from salt burn. Wetlands shorn of grasses, exposing mud flats pitted with puddles. Trees dangling bands of twisted metal, plastic bags and bits of cloth from branches stripped of leaves.
Katrina and Rita swept over southern Louisiana, they left their imprint on the landscape. Using data collected to assess the storms’ effects, scientists are redrawing maps, refining hurricane modeling and improving techniques of coastal restoration.
From Big Picture to Fine Detail
Following Katrina and Rita, John Barras, a scientist with the USGS National Wetlands Research Center, has been mapping changes in Louisiana’s coastal wetlands. In some areas, vegetation was torn from its roots to expose a muddy marsh floor. In other places the marsh soil and plants were ripped apart and pushed aside, allowing new bodies of open water to form. “Satellite images make the breaks in the marshes look like one big pond,” Barras says, “but when you get closer to them, you can tell there are a few very large areas — areas over 500 acres — but most of the damage to the wetlands is from many, many smaller tears, rips and shears in the marsh.”
Words That Picture Marsh Damage
Scientists in the field often describe the effects of storms on the wetlands with colorful terms. Here’s a glossary of their lingo.
Rolled: strips of marsh mat uprooted and rolled up jelly-roll fashion
Shear: a rip between marsh surfaces that tears marsh and moves it apart, allowing expanses of water to form
Compressed or folded: marsh mat blown into ridges resembling an accordion or, in more aqueous marshes, a crumpled bed sheet.
Scoured: marsh with vegetation ripped off at the roots, exposing a muddy bottom
Inverted or flipped: unbroken marsh mat lifted from its clay base and overturned with roots pointing skyward
Marsh balls: marsh mud and grass pushed together into cinderblock- to sofa-sized clumps and blown about like tumbleweed
U.S. Geological Survey
Barras estimates the deepest of the new open water areas to be three feet; most are probably about six inches deep. The smaller the area of tear or shear, the more likely the marsh is to recover. Larger expanses of damage, such as in Upper Breton Sound or in White’s Kitchen, will probably become permanent lakes.
Barras makes his determination of landscape changes by comparing satellite images taken before and after the storms. Classifying different colors in an image as land or water, Barras looks for new occurrences of water in post-storm photos. “Some areas are so large they are easy to find from the ground,” says Barras, “but you need an aerial view to appreciate the extent of the changes that have occurred.” Fly-overs in small aircraft and field verification of conditions on the ground provide more detail about specific sites.
Preparing for Future Storms
Based on data gathered from past storms, hurricane modeling predicts the behavior and consequences of future storms. Assessments of Katrina and Rita will help refine modeling, to show when and where the fastest winds and heaviest rains are most likely to occur. The assessments contribute to public safety by increasing the veracity of weather forecasts, giving prudent warning to people in harm’s way while reducing the disruption and costs of unnecessary evacuations.
Assessments also influence coastal restoration efforts. By analyzing the performance of various projects during and after the storms, scientists and engineers can fine-tune techniques to increase their endurance or boost their protective capacity. For instance, observation of which plants best withstood high winds, or how the electronic components of water control structures fared in a storm surge, will affect future decisions and factor in evaluations of a project’s cost effectiveness.
An Uncertain Prognosis
Within weeks of the hurricanes, the environment showed signs of recovery. Trees budded with unseasonable new growth, and sprigs of vegetation showed green in scoured areas of the delta.
But the lasting effects of the hurricanes are difficult to predict. How much of the estimated hundred square miles of lost land will remain open water? Will the freshwater marshes that were drenched with salt water turn brackish or convert to open water? Will fisheries dependent on the wetlands for food and habitat rebound? And how much of the wetlands’ protective capacity remains as a new hurricane season approaches?
“It’s impossible to tell the extent of damage yet,” Barras says. “It may take a year, two years, to determine what changes are permanent. Scientists will continue to monitor and evaluate Louisiana’s coast to answer these questions and many more.”