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Defining Coastal Sustainability

By: Lauren Alleman

“Coastal sustainability” is a phrase you’ll hear with some regularity in the wake of Hurricane Sandy.

What does the phrase “coastal sustainability” mean to you? Do each of us define it in the same way? To an engineer, a sustainable coast might be one that includes hard structures like seawalls to control flooding and allow humans to live in low-lying areas. To an economist, a sustainable coast may be one has several industries such as tourism, fishing, shipping, and manufacturing rather than a single economy. To a coastal ecologist, a sustainable coastline has layers of wetlands, oyster reefs, and barrier islands that act in concert as storm energy dissipaters.

Wetlands have been adjusting to rising and falling sea levels for thousands of years. The shape of our coastline looked different during the last ice age, and will look different in 100 years. Wetlands are incredibly effective at absorbing flood waters and filtering pollutants, but they do have limitations to how much water they can handle.

Wetlands are programmed to adjust their productivity to match the hydrology of a site through an elegant feedback loop.

Feedback loop wetlands use to adjust their productivity.  Image courtesy of USGS.

Feedback loop wetlands use to adjust their productivity.
Image courtesy of USGS.

When sea-level rise happens at a slow enough rate, plants can adjust by increasing productivity and adding roots to the soil, where they are slow to decompose in the aerobic environment, and eventually become peat. This effectively raises the elevation of the plants to their optimal level. Sediments suspended in the water help sustain the elevation and stimulate growth when they are deposited on the surface of the marsh or swamp. However, when sea level rise happens too quickly or there is not enough sediment deposition, the plants become submerged and drown.

Current estimates from NASA estimate a global sea-level rise rate of 3.16 mm/year. In New York, this will rise sea-levels a total of 2.3 feet by 2100. The flooding that would occur with an increase in sea level would impact much of Long Island, Brooklyn, Staten Island, and Queens. Check out this interactive map which shows what coastal cities would look like if if there is no coastal protection.

How our coastline will look in 2100 based on sea-level rise estimates. Image courtesy of National Geographic.

How our coastline will look in 2100 based on sea-level rise estimates. Image courtesy of National Geographic.

The few remaining wetlands that do protect New York City, such as Jamaica Bay, will have a hard time keeping up with this rate of sea-level rise. Those that attempt to migrate upslope will encounter hard edges, piers, seawalls, and structures that will prevent them from settling into a new equilibrium. This is referred to as “coastal squeeze”, the process where natural migration of habitats is prevented by human infrastructure.

In recognition of the anticipated impacts of this sea-level rise on New York City there is healthy debate around what should be done to protect the coastline. The U.S. Department of the Interior allocated $162 million to 45 projects along the Atlantic Coast, from dam removal to beach restoration. Additionally, the Hurricane Sandy Rebuilding Task Force has initiated a competition called Rebuild by Design that challenges engineers, landscape architects, and ecologists to envision sustainable solutions to areas impacted by Hurricane Sandy. The winning design concepts will be eligible for funding by the U.S. Department of Housing and Urban Development in 2014.

Planning for coastal sustainability means forecasting the areas that will be new coastline and planning our roads, cities, and parks around them.

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