The risk of a beach disappearing
Science | geology
Erosion becomes a problem when human activity begins to occupy a significant area of the active part of these ecosystems.
Most of the beaches are located on the coasts, some in rivers and lakes, and they are places to enjoy and admire. They are part of the coastal zone that is called 'active danger'. Many of these areas, mainly the beaches, are at risk because, over many years, there has been a permanent human invasion without taking into account the dynamics of the sediments. There is a specialty of science and engineering (in Spain within that of Roads) that studies and simulates the dynamics of the coast and beaches, but the results of these studies have only recently begun to be applied and in many cases it is already too late.
Beaches are dynamic systems that undergo constant changes, normally cyclical, due to the waves that break on their shores. If they survive, it is thanks to their ability to respond to the high-energy dynamics associated with waves. One of the effects of waves is erosion, which is associated with the transfer of sand from one place to another. In this process, the active part of the beach, called the envelope, plays a key role.
The part of the beach that is above low tide and the dunes are the main store of sand to respond to storms. Depending on the location (open sea, protected coast, river mouth...), the beaches experience from annual cycles to decades and, in terms of their natural movement of sand, lateral movements of tens of meters and vertical movements are observed. up to 5 meters.
One of the mechanisms for the transfer of sand is the rip current, which transfers sand from the high areas to the sea. An important role is played in this mechanism by the so-called bars, which act as mobile obstructions for the waves. These bars, in low energy areas, are close to the shore, but in high energy areas they move away from it. This is well known to surfers. All this dynamic tells us that with erosion, which is a natural process, sand is not lost, it is moved to another place either along the coast or out and back in again. These processes reach their greatest magnitude in cyclonic regions.
sustainable coastal management
The entire process that keeps the beach in balance is called negative feedback or automatic adjustment and seeks to reduce the energy of the waves that impact the beach. The process becomes positive when the movement of the sand increases the energy of the waves. For example, in front of a boardwalk, when the depth increases. Thus, the study of the size and dynamics of the beach envelope is essential for sustainable management of the coast.
Erosion becomes a problem when human activity begins to occupy a significant area of the active part of the beach or diverts the natural directions of the waves. For example, removing dunes or building breakwaters or dikes. In many places, man-made infrastructure falls squarely into coastal risk areas. For this reason, it is interesting to evaluate, for these areas, the risks derived from erosion. A 30-meter recession of a change of coastline on a beach with its dunes and free surface behind them is not the same as in a place where the infrastructures (homes, roads, etc.) reach the coastline.