Page 107 - (DK) Ocean - The Definitive Visual Guide

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Coastal Defenses

Coastal defense refers to various types of engineering
TYPES OF DEFENSES
techniques aimed at protecting coasts from the sea. The
threats posed by the sea fall into two main categories. SEA WALL A sea wall is
designed to reflect wave energy.
First is the danger of flooding of low-lying coastal
Modern walls have a curved top
areas during severe storms. Second is the continuous that prevents water from spraying
over the wall in storms. A wall
gradual erosion of some coasts. There are a number
protects the land behind it for
of different approaches to coastal defense. To prevent some years but usually increases
flooding of low-lying regions, one solution is to erosion of the beach in front of it.
build a large-scale system of dams and tidal barriers.
Another is to encourage the development of natural
barriers, such as salt marshes, around coasts, and to
conserve existing areas of this type. A third possibility ROCK GROYNE This
is managed retreat. Instead of trying to hold back consists of a pile of large
the sea, some areas of coast are allowed to flood. HARD ENGINEERING rocks built out from the
shore. The aim is to slow
The idea is that, in time, the flooded land will turn erosion by causing a local
into a marsh, providing natural protection. buildup of sand, but it can
To slow coastal erosion, various “hard” engineering aggravate erosion nearby.
techniques are commonly employed, such as the
DUNE STABILIZATION Coastal
building of sea walls, breakwaters, or groynes. These dunes provide valuable protection
methods can be effective for a while (they usually against erosion if they can be
stabilized and prevented from
have to be rebuilt after a few decades), but are shifting. This is usually achieved
expensive and can increase erosion on neighboring by planting
with grasses.
areas of coast by interfering with longshore movement
of sediment. “Soft” engineering techniques are more
environmentally friendly. They include the temporary
solution of beach nourishment (see panel, right), BEACH NOURISHMENT
which has to be repeated every few years, and This involves adding large
encouraging the development of coastal dunes. SOFT ENGINEERING amounts of sand to a beach.
Waves and tides spread the
material along the coast,
Crumbling Coasts temporarily building up
its natural defenses.
In 2000, the US Federal Emergency Management Agency
estimated that as many as 87,000 houses in the US are in GEOTUBE A geotube is a long,
danger of falling into the sea by the year 2060. Among them cylindrical container, over 8 ft
are the condemned houses, pictured below, on eroding cliffs (2.3 m) in diameter, made of a
at Governors Run in Chesapeake Bay, Maryland. In California, durable textile or plastic and filled
about 86 percent of the coast is actively eroding. Similarly, with a slurry of sand and water.
stretches of the eastern coast of England are eroding at a rate Different types can be laid along
of up to 6 ft (1.8 m) a year—the highest rate in Europe. the top of a beach, or inside a
Coastal defenses can slow coastal erosion temporarily, but in MODERN SOLUTION dune, or just offshore, where they
reduce coastal erosion and protect
the long run maintenance will become prohibitively expensive. beachfronts. This tube is part of
In the end, the sea will triumph. the Barren Island Tidal Wetland
project in Maryland.

DAMS AND STORM-SURGE BARRIERS The Netherlands has
invested in an extensive series of engineering works to protect a
large region of the country from future marine flooding. Known
as the Deltaworks, it includes many dams and movable storm-
surge barriers. The works were initiated in 1953 after a serious
storm and floods killed a total of 1,835 people.

LARGE-SCALE PROTECTION OCEAN ENVIRONMENTS