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About Beach
and Coastal Erosion
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About Beach and Coastal Erosion
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Beach erosion and coastal erosion
are not the same, but they are related. Beach erosion is a
reduction in the amount of sand a particular beach has. On
a global level, sea level rise causes beach erosion. But beaches
also erode (and expand) on a seasonal basis.
Beaches get sand from both the ocean and the land. Larger
waves move sand from the coastal sand dunes off into the ocean.
This raises the seafloor, flattens the overall profile of
the beach, and, therefore, causes waves to break further offshore.
This, in turn, minimizes the waves' impact on coastal lands.
Beaches recover from these seasonal shifts when the waves
move the sand back onto the beach and the winds blow the deposited
sand into dunes. These dunes will store the land-based sand
until the next large wave event.
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Coastal erosion occurs when the beach migrates
toward the land in order to compensate for beach erosion as it tries
to maintain a constant supply of sand (see the right side of the
photo). If sand is not available to a beach, such as when a wall
is built to protect the land, the land is stabilized, however beach
erosion will occur (see left side of photo).
Installing a seawall or revetment (i.e., hardening a shoreline)
interferes with the natural cycle of beach erosion. Rather than
pulling sand from a landward supply in order to promote waves breaking
further off-shore during the seasonal high wave period, the seawall
or revetment prevents this natural phenomena from occurring. Thus,
the land itself begins to erode.
Therefore, it is tragically ironic seawalls or revetments have
been installed to prevent coastal erosion, but their very presence
exacerbates the very problem they were supposed to resolve.
Source: Fletcher, Charles, Eric Grossman, Bruce Richmond. Atlas of
Natural Hazards in the Hawaiian Coastal Zone. 2000. |