This post belongs to a special series of posts written by students in Dr. Simon Engelhart’s Coastal Geologic Hazards course at the University of Rhode Island. In this course students learn about coastal processes, including storm surges and sea level rise, and how these impact people and the environment.
As global climate changes, sea levels rise, and storms become increasingly intense; as a result, coastal flooding is becoming increasingly more important. Coastal communities have a number of options to combat this problem, including using conventional engineering solutions like sea walls and other hard structures. Nature has its own solutions to deal with this problem. Natural barriers such as oyster reefs, mangrove forests, and salt marshes, break up wave energy and limit how far inland waves or storm surges can penetrate. Unfortunately, as society has developed along coasts, we have impacted natural barriers in a variety of ways.
New York Harbor, for example, was home to 350 miles of oyster reefs in the 1600s.1 By the 1930s, however, the oyster beds were closed due to the combination of over-harvesting, sewage pollution, dredging, and landfill. Boston is another example: In the 1600s, Boston as we currently know it did not exist. The beginnings of the city sat on an 800-acre peninsula surrounded by salt marshes. Through time, over 5,000 acres of these salt marshes were filled in to make what we now know as Boston. With these natural barriers gone, coastal communities are left more susceptible to flooding. That does not mean, however, that these communities need to resort to conventional engineering solutions to prevent coastal flooding.
Nature vs. engineering – who wins?
While many conventional engineering solutions do exactly what they are supposed to (prevent flooding), there are a number of unintended consequences. An example of this is described by Stijn Temmerman (University of Antwerp, Antwerp, Belgium) and his colleagues in their paper Ecosystem-based coastal defence in the face of global change. In their study, the authors describe conventional solutions the Netherlands installed as a flood defense system. The unintended consequences of the installed sea walls and floodgates include estuaries being cut off from the sea, the erosion of tidal habitats, and the appearance of toxic algal blooms that, in enclosed or semi-enclosed systems, can kill aquatic life. As an alternative, Temmerman and his colleagues argue that we should be using nature to fight nature. Instead of building a wall, we should create or restore a wetlands, build an oyster reef, or create and restore natural coastal features so we can let nature do its work. Why? Because the unintended consequences of natural solutions tend to better the environment around them.
Oyster reefs can dramatically improve water quality: a single adult oyster can filter up to 50 gallons of seawater a day! How about creating wetlands? You’ll be benefiting the local fish population, as 70% of commercial fish depend on salt marshes for part or all of their lives. Wetlands also play a role in fighting climate change, as they can sequester (capture) carbon.
It is important to note that there are downsides to both conventional and natural solutions. Space is a big requirement for natural solutions. This requirement alone may prevent larger cities from being able to implement natural solutions. While both natural and conventional solutions are expensive, the distribution of costs differs. For natural solutions development and installation have big price tags, but maintenance costs are lower. On the other hand, conventional solutions benefit from lower installation costs but are plagued with higher maintenance costs and the likelihood to play catch up and build higher walls with rising sea levels.
Success stories of natural solutions
There is no doubt that coastal communities need to take steps in order to combat coastal flooding. Just as each community is different, the solutions will be different across the globe. Some areas may simply not have the space required for natural solutions. Others may not be able to afford the upfront costs of natural solutions. However, due to the added benefits of natural solutions, cities and towns should focus their efforts on implementing natural solutions, if at all possible. Nature should be used to fight nature. In some places this is already beginning to happen.
The Billion Oyster Project and the Massachusetts Oyster Project are working to restore oyster reefs in New York and Massachusetts. The organizations behind these projects do great work. Restaurants donate oyster shells (that would otherwise go to a landfill!) to both organizations so they can be used as the base of an oyster reef. In order to grow, oyster larvae must attach to a hard substance; turns out, recycled oyster shells are perfect for this. Additionally, the Massachusetts Oyster Project partners with local organizations to run upwellers, which raise baby oysters (called spat) up to 1 inch in size to jump start their life cycle and give them a better chance of survival when put in the water. Upwellers run a constant supply of seawater over the spat so they can get nutrition from the water without the threat of predators. Along the Gulf Coast, a coalition called Restore the Mississippi River Delta works on projects such as marsh creation, barrier island restoration, and oyster reef restoration in order to protect the coast of Louisiana. This organization has scientists that provide technical expertise for these projects, policy experts that highlight the economic benefits of these projects, and outreach staff that educate the community. Hopefully other communities will follow suit and begin implementing natural solutions to combat coastal flooding.
Casey Dannhauser is currently working towards a Masters of Oceanography at the University of Rhode Island. When she isn’t focusing on her schoolwork she can be found working to improve the coastal water quality in Cotuit, Massachusetts for the Barnstable Clean Water Coalition.
Logan Thomas is a senior undergraduate at the University of Rhode Island pursuing a degree in geology with interests in the GIS field.
Featured image: The Oosterscheldekering, a storm surge barrier built in the Netherlands. Photo courtesy of the Rijkswaterstaat Image Archive.