With the threat of rising sea levels, the New York City government has to seriously consider how to protect its land. New York is not only threatened by elevation of the water level, which could decrease the size of coastal areas, but also by the increasing damage that could be caused by storm surges. One way that the coast could be protected is by building barriers.
Examples of barriers include seawalls, groins, and jetties. Seawalls are exactly what they sound like, walls built in the sea, which protect the coast from being inundated with too much water (Gornitz et al. 2002). Groins are a series of posts or sometimes a wall, built onto a beach that is meant to catch littoral sand that is moved by the currents. Jetties are long strips of land that make inlets stable and protect harbors from the worst effects of waves. The decision of where to place barriers and what kind of barrier to use is vitally important, both to the area it protects and the ecosystem it affects.
After the disastrous effects of Hurricane Sandy, New York City had to consider what can be done to protect itself. One option that was first thought of was to build moveable barriers in the ocean, like those found in the Netherlands. (Sobel 2014) There are examples of barriers like that as close as New England, protecting small channels from being flooded with water. But those types of barriers only work for small areas. The shores of New York are too long to be protected by a moveable barrier. Bryan Walsh wrote in Time that a Dutch-style barrier surrounding New York City from Sandy Hook, New Jersey to Rockaway Beach would be an option, but would cost anywhere around $10 – $15 million (Walsh 2012). Christa Marshall in Scientific American wrote about a proposal to build two different seawalls, first a seawall in the East River, then a seawall from Sandy Hook to Rockaway Beach (Marshall 2014). This double seawall would create an extra layer of protection. It is doubtful that this will completely stop all flooding, but it would limit the amount of damages that would occur in New York. Still, though barriers are able to stop water from damaging the land, they also have great consequences.
The greatest consequence of coastal barriers is erosion. With seawalls, erosion occurs both at the base of the seawall (Gornitz et al. 2002) and further down the coast where the seawall does not extend. These areas suffer even more than they usually would because the seawalls just move the waves further along and when they reach an unprotected area, the waves are even more powerful than normal (Dunn 2009). If rubble is placed directly next to the seawall, erosion at the base can be decreased. Groins, if they are not placed in the right spot usually increase erosion of beaches further downstream, as do jetties. Erosion of beaches causes habitat loss for animals who nest or lay eggs there and can decrease the number of invertebrate species who live on the beach (Dugan and Hubbard 2010).
New York must consider the cost of building barriers. Though they might protect the city from flooding, they could also pass the consequences further along to other cities. Building barriers is considered to be a “hard” approach. In the next science post, I will investigate a “soft” approach, beach nourishment.
Dugan, J.E., and D. M. Hubbard. 2010. Ecological Effects of Coastal Armoring: A Summary of Recent Results for Exposed Sandy Beaches in Southern California. US Geological Survey, Department of Interior. Scientific investigations report, 2010-5254. Reston, VA, USA.
Dunn, P. 2009. Can Seawalls Prevent Beaches from Eroding?. MIT School of Engineering. http://engineering.mit.edu/ask/can-seawalls-prevent-beaches-eroding
Gornitz, V., S. Couch, and E. K. Hartig. 2002. Impact of sea level rise in the New York City metropolitan area. Global and Planetary Changes 32: 61-88.
Marshall, C. 2014. Massive Seawall May Be Needed to Keep New York City Dry. Scientific American. http://www.scientificamerican.com/article/massive-seawall-may-be-needed-to-keep-new-york-city-dry/
Sobel, A. 2014. Storm Surge: Hurricane Sandy, Our Changing Climate, and Extreme Weather of the Past and Future. HarperCollins. New York, New York, USA.
Walsh, B. 2012. Sandy: What a Coastal U.S. Can Learn from Other Threatened Cities. Time. http://science.time.com/2012/11/05/sandy-what-a-coastal-u-s-can-learn-from-other-threatened-cities/