image: Army Corps of Engineers
With another hurricane season beginning, people living on AmericaÕs coasts wonder if this is the year their home will be targeted by a major storm.
But more troubling is that all 30 states bordering the coast and shorelines of the Great Lakes have problems with coastal erosion. In fact, a recent report by the Federal Emergency Management Agency (FEMA) states that more than1,500 houses along these coasts will be lost this year, and 25 percent of homes and other structures within 500 feet of the shorelines will fall victim to the effects of erosion within the next 60 years.
Erosion patterns and severity vary regionally, as they are a result of local geological and environmental factors such as winds, tides, and the frequency and intensity of coastal storms. Some coasts, such as those of the barrier islands in the Southeast, are retreating 25 feet per year, and sections of the Great Lakes coastline have receded by as much as 50 feet per year.
|image: Army Corps of Engineers|
But while some erosion is naturally an ongoing process, all it takes is a single severe storm to destroy an entire beach or to wipe out an entire system of dunes. Storms and the resulting erosion cause billions of dollars in property damage every year.
"We are used to thinking of a landas we call it, terra firmanot changing a lot", says Cornelia Dean, science editor at the New York Times and author of Against the Tide, a book on coastal erosion. "Mountains may be eroded to the sea over hundreds or millions of years, but beaches change much more quickly. You can see them change in an afternoon."
On top of that, some scientists believe that global warming will make storms stronger and more frequent. But no one can say yet for sure. It is known, however, that sea level is rising in many regions and that global warming may increase the rate of rise. The sea level has increased by 10 to 25 cm over the past 100 years and NASA scientists predict that the sea level could rise 40 to 65 cm by the year 2100. Such a sea level rise would threaten coastal cities, forcing them to attempt to hold back the sea or to retreat.
|image: Environmental Media|
Humans have also significantly increased the rate of coastline erosion. Population pressures, through economic development and recreational use, have exploited even the most remote coastal lands. In the last century, confidence in American technologys ability to engineer solutions has led many coastline property developers to risk placing structures closer and closer to the water.
Protecting these structures from eroding away with the shoreline is both expensive and difficult, as is rebuilding or replacing damaged structures. And all Americans bear the cost of this battle with Mother Nature through their state and federal taxes. Dean says the ultimate solution is to convince communities to adopt a policy of retreating with the coastlinean idea thats unpopular with property owners and communities whose economies depend on beach development.
|A groin field|
image: Environmental Media
The Army Corps of Engineers defends the nations coastline against erosion using two main strategies: erecting hard structures to protect sand and buildings, and replacing lost sand by "replenishment" or "renourishment." Typical defense structures include long jetties or breakwaters made of rocks or concrete, shorter and more closely spaced groins (often built to protect individual private tracts of beach; see image at right), and seawalls, usually made of steel, to retain sand in front of buildings on eroding beaches.
But, as Dean points out, such "armor" may do more harm than good. Interrupting the natural flow of sand along one beach may rob other nearby beaches of natural sand replacement. Beaches with structures as protection from storms may only be diverting the storms energy to adjacent beaches. Such structures may also severely disrupt coastal ecosystems. "What people have done in building a wall is they have chosen to protect the house or the store or the condorather than the beach," says Dean. "I think thats a mistake."
Joseph Vietri of the Army Corps of Engineers New York District wont rule out any one strategy. "I think theres been a growing trend in the past 15 years away from hard structures such as rocks, groins, and so on," he says. "But thats not to say that theyre not tools that should be considered in certain specific locations. I would not preclude the consideration of a structure if appropriate in a certain location."
Replenishment projects involve the trucking, pushing or pumping of sand to restore or rebuild eroding beaches. While some view this strategy as less disruptive, it is both extremely expensive and extremely temporary. A study by Duke Universitys Program for the Study of Developed Shorelines summarizes the staggering amounts spent on beach replenishment around the United States.
Dean argues that we should leave the pattern and extent of erosion to the sea. "I would say the biggest mistake to be made on a beach suffering from erosion is to try and stop the erosionthis is not a process we can stop." But Vietri says human intervention is necessary to protect property and quality of life. "I dont believe that Mother Nature should be allowed to take the course in every particular situation," Vietri says. "I feel that man has manipulated the system to the extent that Mother Nature might need some help."
Options for Action
Several coastal states, including Florida, North Carolina, New York, Massachusetts, and Maine, have taken or are considering steps to halt the construction of seawall defenses. North Carolinas Coastal Resources Commission adopted a prohibition on such structuresin essence, a call to retreat. Some towns are now prohibiting further development of their beaches.
Environmental and taxpayer advocacy organizations like Coast Alliance favor the enforcement and expansion of laws restricting beach development, and are lobbying for reforms in programs like National Flood Insurance that subsidize developers. Just as actively, organizations like The American Coastal Coalition insist on the vital economic value of beach development and the governments responsibility to protect it.
For those who still choose to build their castles on the sand, scientists at Duke have scrutinized the risks and benefits of the many alternative devices for shoreline stabilization. And the Federal Emergency Management Administration (FEMA) advises ways to prepare for the inevitability of storms.
Elsewhere on the web:
Army Corps of Engineers - Coastal Engineering Research Center
Program for the Study of Developed Shorelines at Duke University
NOAAs State of the Coast report
The United States Geological Service Coastal and Marine Geology Program
"The Beaches Are Moving" video produced by Environmental Media, Inc.