Seawalls – Our Front Lines of Defense
Various (Washington Post, Seattle Times)
Is there a person in the world that doesn’t like to sit on the beach, take a short break from the daily grind, and enjoy the beautiful ocean scenery?
Unfortunately, due to climate change, global sea levels are rising and people who like to enjoy the shoreline are no longer able to do so, as many coastal cities are literally sinking, and the most common solution today is paving our shorelines with hard armor, especially, seawalls.
More and more seawalls are being built along coastlines all around the world, creating a barrier of protection from sea-level rise and extreme storminess. These are physical walls, made primarily of concrete or rock, that serve as barriers between the sea and people living on the coast. You’ve probably seen them and not even noticed them. Most seawalls go unnoticed, these grey dull surfaces integrate with the urban landscape, as can be seen in the images from Vancouver, Canada, and even Hawaii, where you’d expect beautiful sandy beaches.
The rich history of seawall construction can be traced back thousands of years to the Eastern Roman Empire. The first seawalls are commonly attributed to the Roman Emperor Constantine I, also known as Constantine the Great, who ordered their construction in 448 A.D. The original marine barricades were built as part of a larger defense system designed to safeguard the city of Constantinople (present day Istanbul, Turkey) from attackers by land or sea. They were erected along the mainland wall and bordered the city’s Propontis side (on the Sea of Marmara) as well as Khrysoun Keras (on the gulf of the Golden Horn).
The construction of seawalls has been traced back thousands of years ago to Eastern Roman Empire. Historic seawalls made from Roman/Natural cement like in Caesarea are still holding. These structures have been proven to be so effective and strong that they can withstand decades of wear and tear from the evolution of human societies and extreme weather events.* After so many years they develop rough features and imperfections that allow for marine life to sustain. However, in recent times, modern seawalls are designed and built with little or no environmental considerations. The construction of seawalls comes at a grave cost to natural coastlines, creating a direct loss of natural coastal habitats, replacing them with unproductive, featureless, man-made structures. Studies show that seawalls typically support lower biodiversity and habitat quality, than natural shorelines, negatively impacting the ecosystem. In addition, current engineering requirements typically call for a 30 or 50 life span for the structure, leading to frequent maintenance/retrofitting, that inhibit the development of diverse and stable marine communities. Standard “grey” seawalls thus provide their engineered function, serving as massive concrete barriers, protecting against upland erosion and surge flooding. But using principles of ecological engineering, they can do so much more! Read on to the end of the blog to learn how.
First Steps Toward Ecological Thinking in Seawalls
Still in Canada, the seawall of Vancouver’s convention center got upgraded to ecological habitat with a unique “habitat Skirt”. While not a structural element, this habitat addition created opportunities for mussels, algae and barnacles at the intertidal zone.
Are you planning on visiting Seattle soon? Next time you visit there, search for Seattle’s downtown waterfront. You should check out the new seawall project. Not only that this seawall was built to last more than 75 years, but it also was developed to create enhanced fish native habitat.
The structure, completed in 2017, was designed with few elements in mind:
Light penetration surfaces; habitat benches to provide hiding places for fish; and texture of the structure to promote growth of fauna.
Apart from replacing the old city’s seawall that needed reconstruction and retrofitting, the main ecological goal of Seattle’s new seawall was to boost the region’s iconic Chinook Salmon, listed under the US Endangered Species Act. The biological monitoring of the Seattle seawall has started a few months ago and is still in progress. Initial results indicate that the new seawall is easing the Salmons passage.
“The UW team saw an estimated 10,000 juvenile salmon of various species on a single day of surveying last May and as many as 300 chinook on another day the same month.”
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