Waves have always pounded at the bluffs of California’s coasts, shaping the dramatic and beautiful marine landscape that so many of us call home. However, the iconic California coast is beginning to disappear under the sea as climate change pushes waves to surge greater than 9 feet in the coming century. Officials in the San Francisco area are taking steps to move the iconic Great Highway away from Ocean Beach due to severe coastal erosion, and have been forced to declare houses and apartments in Pacifica uninhabitable as mounting waves swallow the crumbling seaside cliffs.
What is coastal erosion?
Coastal erosion refers to the gradual loss or displacement of land due to natural and human causes. Natural energy sources such as waves and tides, exacerbated by the impacts of climate change, accelerate storm frequencies and sea levels, which results in the long term loss of sediments in the coastal zone. Erosion applies not only to the coastal land strips, but also to the strip of sea floor immediately bordering the coast.
Most of our exposed coasts lose land because of this process called erosion, the periodic wearing away of sediment and land from dynamic agents. Where the tide is low, there is significantly less erosion. For example, in the Mediterranean, the tidal range is low and cliff faces are less eroded by natural marine processes.
The tide in particular plays a significant role in eroding coastal shores, spurred by the movement of water in high waves and strong currents. The tide has a twofold role in the molding of coastal landforms: 1) tidal currents transport quantities of sediment and erode bedrock 2) periodic changes in the rise and fall of the tide distributes wave energy.
Tide Erosion and Transportation
The tide carries sediments, transporting physical materials that erode coasts with the ebb and flow of ocean water. Waves can be the cause of major sand deposition, moving sand each time waves crash against the beach. Deposition is when physical materials are carried by the sea and deposited or left behind on the coast. These residual motions are very important in local circulation, and tide currents grow stronger the nearer they are to the coast.
Too little sediment transportation can lead to the erosion of riverbanks and coastal areas, diminishing ecosystem quality. Conversely, too much sediment deposition can result in the burying of ecosystems and altering of pathways.
Change in Water Levels
If you’ve ever been to a beach, you surely know what a tide is. But did you know that tides rely on the positions of the sun and the moon throughout the day? The energy exerted by the change in position of the sun and moon have a direct effect on the height of waves, affecting water levels in varying points of the day. This is because tides are defined as the rise and fall of ocean water as a result of gravitational pull from the sun and moon. When the surface of the sea reaches its highest point, this is called high tide. At its lowest point, it is called the low tide. The difference between the consecutive high and low tide is known as the tidal range.
In areas with the largest tidal ranges, water can rise and fall 10 meters, the shoreline consequently moving laterally several kilometers between high and low water. The water level of a sea surface changes throughout the day, depending on the forces exerted by celestial bodies. Various points of the intertidal zone are exposed to erosion and deposition.
Coastal erosion is a ubiquitous process responsible for receding shorelines worldwide. As of today, about 70% of the world’s sandy coasts are marked by erosion. Our home state of California has especially felt the impacts of tidal coastal erosion, coasts receding before our eyes, year after year. A 2017 study found that pepper coastal cliffs from Bodega Head in Sonoma County to the US-Mexico border are at risk of collapse, due to cliff erosion.
How is erosion controlled?
Erosion is a fact of nature. However, human activity and the effects of climate change can accelerate it. Thankfully, there are multiple methods engineers can employ to reduce the process of erosion. Engineers can simply install structures to physically prevent soil from being transported, such as wireframe gabions, which hold boulders in place. These are typically situated on cliffs where erosion may pose a threat to buildings and cars. The gabions affix boulders so that they do not tumble and crush buildings or highways due to the effects of erosion.
Other methods such as living shorelines are used in wetland areas. In marshy environs, engineers can construct native plants, stone, sand, and living organisms along weltand coasts in order to anchor soil to the area, prolonging erosion. This protects coastlines from the wear and tear of erosion, as well as damaging storm surges.
At Erosion Control USA, the Envirolok system is used to provide permanent vegetative solutions that results in minimal impact to the site and the environment. Envirolok is a vegetated environmental system made up of encapsulated soil bags and spikes that reinforce and stabilize soil, making it resilient to erosion processes. The organic nature of Envirolok allows for native plants to take hold of the system, tethering it to the area and making it even stronger over time.