Hurricanes: Foul Winds or Fair?

In the early morning hours of August 26, 1992, Hurricane Andrew slammed into the southern coast of Louisiana. With wind gusts of over 130 mph and a 15-foot storm surge pushing far inland, the storm's immediate impact on Louisiana's wetlands and barrier islands was soon apparent:

• millions of fish killed by oxygen depletion
• 70 percent of the oyster reefs in the Barataria-Terrebonne National Estuary damaged by a blanket of sediment
• major sand losses on 70 percent of Louisiana's barrier islands
• barrier islands stripped of beach and dune vegetation that provided habitat for marine birds
• coastal marshes shorn of above-water vegetation

In spite of these grim outcomes, scientists like Karen Westphal of the Center for Coastal Energy and Environmental Resources say there can also be a fair wind associated with hurricanes, even those like Andrew. "Although they are clearly destructive, in the long run hurricanes can also have positive effects," says Westphal.

Marshes can actually benefit from the effects of hurricanes and related weather systems. First of all, hurricanes typically increase precipitation in the regional area. This added rainfall increases eroded sediment runoff into rivers and bayous. As these water pathways overflow their banks, they deposit the extra sediment in marsh and wetland areas, encouraging wetlands growth. The second beneficial effect relates to the hurricane's storm surge. As this surge rides the front edge of the hurricane front, it pushes water up into Louisiana's marshes and rivers. While this water usually drains out in 24 hours, the sediment it carries is left behind, further nourishing the marsh.

For example, the intensity of rain during hurricanes and tropical cyclones causes high soil runoffs, even when conditions have been dry. As a result, rivers carry high levels of sediment to estuaries threatened by rising sea levels. Storm surges that accompany hurricanes play a similar role by dispersing massive quantities of water deep into the state's marshes. These flood waters normally drain within 24 hours, and according to Dr. Abby Sallenger of the USGS Center for Coastal Geology, "It's absolutely true that this hurricane-caused flooding adds critical sediment and nutrients to marshes." Studies also show that hurricanes generally have little long-term effect on emergent marsh. While foliage may be stripped, the stimulation from new nutrients brought by the hurricane quickly returns the beds to their original condition.

Despite the benefits that hurricanes can provide to coastal wetlands, communities like this one along the Barataria Bay waterway can suffer devastating damage.
(ACOE photo)

Even the erosion to beaches, which is often distressingly obvious, may have benefits to other parts of the coastal ecosystem. For example, in those instances in which hurricanes cut deep into beaches, the result can be the formation of new habitat that supports dunes grasses, salt marsh and sea grasses.

Some scientists also contend that in the long run mangroves and other tree species benefit from the effects of hurricanes. They say hurricanes perform the same cleansing function as forest fires in maintaining the overall conditions for healthy coastal forests.

But Westphal cautions that making the case for the long-term benefits of hurricanes shouldn't obscure the very real and significant negative consequences. "You need to see both sides of this issue," says Westphal. "And that's because fundamentally it's a debate about ecological trade-offs. Just how those trade-offs balance out, however, is going to take a lot more hard data."