Coastal Erosion

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Sea and water levels have been rising for the past 100-years, and the rate has increased in recent decades. In 2014, global sea level was 2.6 inches above the 1993 average – the highest annual average in the satellite record (1993-present). Sea level continues to rise at a rate of about one-eighth of an inch per year.

Higher sea levels mean that deadly and destructive storm surges push farther inland than they once did, which also means more frequent flooding and the erosion of seabed, land, and maritime assets, which has consequences.

For instance, New Orleans is sinking, which is nothing new really, a heavy reminder imparted by Hurricane Katrina and the ensuing devastation. For 300 years the sea has been advancing and conquering, and as coastal and wetland erosion continues, it is estimated that the city will be offshore in 90 years. Presently, entire areas of Southern Louisiana wetlands are disappearing.

And the issue of rising water levels and the resulting erosion is truly a global issue, extending far beyond the riverbanks and shorelines of the United States: similarly, erosion in Europe and Australia is a widespread problem. 20% of the EU’s coastline is affected by erosion (20,000 km) and more than 70 million people are currently affected. Much of that erosion threatens Mediterranean regions (and England/Wales/Ireland/Scotland area). In Australia, the coast is both affected by slow and rapid onset erosion.

What is coastal erosion?

Coastal erosion is defined as “the loss or displacement of land along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms.” (1)

The process of erosion can be divided into four categories: hydraulic action, attrition, solution, and abrasion. Some also include corrosion as a fifth category. Although corrosion is not the same as erosion, wave action transports the corroding material away from the source and amplifying the eroding effects. We have thus decided to include this in our summary.

1) Hydraulic action

Hydraulic action is the process of waves repeatedly striking the face of a cliff. The force of the waves causes the air within the cracks in the cliff to compress, resulting in added pressure. Over time, this mechanism causes structural disintegration within the cliff, leading to material being dislodged and fall into the sea.

2) Attrition

Attrition describes the process of rocks/debris colliding with each other, chipping away at the cliff. This process may in part be seen as a continuation of the first step (hydraulic action), as the dislodged rocks collide with other rocks, or even with the cliff face from which it originated from.

3) Solution

Sea water is slightly basic in nature. However, the oceans are facing increased acidification due to excess carbon dioxide in the atmosphere. Solution refers to the process of rocks dissolving due to the increased levels of acid. Chalk and limestone are particularly vulnerable to acidification.

4) Abrasion

The constant battering of waves causes the affected rock to slowly erode. This process is accelerated when waves carry debris slamming into cliffs, dislodging pieces from higher up on the affected area. The dislodged pieces fall into the ocean, become subject to further wave action and effectively amplifies the problem.

5) Corrosion

As with the process of solution described above, corrosion happens as result of low pH in the ocean. However, coupled with the constant pounding of waves, the mechanism is greatly amplified as the wave action is effective at removing the corroded material.

What influences the rate of coastal erosion?

With an understanding of how coastal erosion works, it is critical to investigate the factors that influence the speed of which erosion happens.

 The most basic factor is the hardness of the rocks/cliffs by the coastline. On one hand, you have cliffs primarily comprised of limestone, a softer type of rock that is highly affected by all of the erosion processes described above. The coastline in Dorset is a prime example of this, as evident by the massive erosion taking place. The Durdle Door (see photo below) is a direct result of wave erosion that has made its way through the cliff and created an arch.

 On the other hand, cliffs with a high concentration of granite erode at a slower rate than their softer counterparts. The Atlantic coast of Cornwall is a prime example of granite-dominant cliffs that resist erosion despite the constant pounding from waves.

 The second factor that affects the speed of erosion is the presence of cracks, which plays an integral part in the hydraulic action discussed above. Further, the presence of silt and/or sand adds a substantial and significant abrasive effect to the wave action, which further amplifies the level of coastal erosion.

 The third factor critical to rate of erosion is the power of the waves themselves. In simple terms, the force of the wave action is determined by two variables, wind speed and “fetch length”, which is the horizontal distance of which wave generating winds blow.

Coastal erosion in the United States

The economic implications of coastal erosion are vast, especially as increasing amounts of people and assets concentrate in coastal areas. Coastal land is gradually disappearing and coastal assets are subject to high levels of risk for loss. In the US, the entire coastline is subject to the damaging effects of coastal erosion. However, some areas are eroding at a much faster rate, such as:

  • The Gulf Coast
  • New York
  • California

The Gulf Coast

Focusing on Louisiana, the state has received significant attention in recent times due to the sheer magnitude of damages caused by both coastal erosion and flooding. Further, Louisiana is America’s energy coast where thousands of oil rigs and wells are owned and operated. Additional energy-related infrastructure includes refineries and a vast network of pipelines that spans thousands of miles across the state. As with all the states in the Gulf Coast, Louisiana is especially prone to hurricane landfalls and the devastating effects of flooding and erosion. On average between 1985 and 2010, the state has lost nearly a football field sized portion of land every hour, a process that has been accelerated by extreme weather events such as Hurricane Katrina, Rita, Gustav and Ike.

Although such storms are relatively rare events, there is no indication of a slowdown in damages from tropical hurricane activity over the next 25 to 50 years. Sea temperature is the main contributor to favorable environments for hurricane formation and intensification, and surface sea temperatures in the MDR (Main Development Region) in the Atlantic are projected to continue rise. An additional expected long-term development is the intensification of hurricane related rainfall, which causes further flooding and erosion in affected areas.

One of the most reputable studies on the economic implications of coastal erosion, the Richardson/Scott study, suggests that a 3-week disruption of oil deliveries from Louisiana would cost more than 30,000 jobs over the course of a year, resulting in a $1bn loss of US household earnings. The study also suggests that over the next 50 years, such extreme events that threaten domestic oil production and distribution may happen more frequently and in tandem. The study also investigated the potential effects of several commercial activities being halted over a short period of time due to severe storm impact (natural gas production, transports along the Mississippi River, fisheries, etc.), and concluded that the US would suffer a loss of 51,000 jobs and lost earnings amounting to $1.7bn.

In recent years, several initiatives have been launched in order to tackle erosion threat to the state and its industries. In 2017, Louisiana passed legislation for the 50-year plan, an initiative to spend $50bn on coastal restoration and hurricane storm surge protection. At least $10bn of the funds is expected to come from fines paid to the state for the Deepwater Horizon disaster. However, the funds will not stop future economic losses in areas where water meets land. Given a successful execution of the planned activities, Louisiana will still suffer estimated $3.7 billion in annual flood damage.

Florida’s shoreline is also vulnerable to extreme weather events, as the coastline faces both the tropical Atlantic, a main development region for Hurricanes, and the Gulf of Mexico, another high-risk area for hurricane formation. According to a recent report from the Florida Department of Environmental Protection, it is estimated that Florida currently has about 420 miles of shoreline subject to critical levels of erosion. In the past three years, Florida has spent $100 million on pouring additional sand onto the beaches, only to see the sand be washed away shortly after. For a state that generates $55bn in revenue per year from beach tourism, beach erosion is a crucial and multifaceted issue requiring successful large-scale planning and execution over the next decades.

New York/New Jersey

Similarly, New York is facing issues of their own. Post Hurricane Sandy, the landscape of New York’s coastal communities has been radically altered, and years of work lie ahead before the coastline will be ready for another major storm or hurricane. Nearly $20 billion has been set aside for coastal protection projects in and around New York City.

California

According to Scripps Institution of Oceanography, 44% of California’s coastline is vulnerable to erosion. In 2017, San Francisco experiences its worst erosion in 150 years, with the sea reclaiming 180 feet of beach at the most dramatic point. The situation calls for difficult choices to be made. A recent USGS study suggested we can either save public beaches enjoyed by millions, or close them off with rip rap or armoring in order to stop the waves from eroding the coastline further in an attempt to save at-risk homes. The study projects a total cliff loss of roughly 300 million meters by year 2100. To put things in perspective, this would equal 30 million dump trucks filled with eroded material removed from the coastline.

Although the focus in this section has been on the most drastic economic implications of coastal erosion in the US, the challenges described above are commonplace for coastal communities all over the world.

In addition, offshore and onshore maritime installations and assets are influenced by continuous erosion and corrosion, resulting in substantial economic loss and dangerous situations for human and sea life. The platform legs and splash zones on oil rigs, wind turbines, bridges, and piers are damaged from waves and debris that comes in contact with the structures. Oil and gas pipelines, ports, wharfs, quays, docks, and the seafloor of marinas are similarly damaged by erosion and debris.

Conclusion

A tremendous amount of land and maritime assets are currently eroding despite the development of a wide range of protective measures. The prospect of further water level increase coupled with the heritage of mismanagement in the past imply that erosion will be a growing concern in the future. Erosion will continue to pose challenges and risks for as long as there is life on earth, and can thus never completely be controlled. However, it can be managed more effectively and in an economically and ecologically sustainable fashion. Without improved solutions of erosion control, the human, economic, and environmental impacts will be tremendous.

Sources

(1) Ueberman, A.S. and O’Neill Jr, C.R., 1988. Vegetation use in coastal ecosystems. Cornell Cooperative Extension Information Bulletin 198, Cornell University, Ithica, New York. 32 pp.