Geoscience Reference
In-Depth Information
Though effective, these programs are very costly. In the very small
state of Delaware, for example, over 2,300,000 m
3
(3,008,286 yd
3
)
of sand has been used to nourish beaches since the early 1960s at a
cost in 2010 dollars of over $60,000,000. In the tourist-dominated
state of Florida, the cost to nourish beaches over the same length of
time has been over $432,000,000 in 2010 dollars.
One way that people nourish beaches is simply to bring fresh
deposits of sand into a beach system to replenish sand lost through
erosion. In this manner of beach maintenance, which usually oc-
curs at the end of the winter storm season, large earth-moving
equipment transports sand from another source to a heavily erod-
ed beach. Another way that people try to maintain a functional
beach is to limit the loss of sand to erosion. The most common
method used to stabilize sand supply is building a simple struc-
ture called a
groin
, which is a low wall built at a right angle from
the shore a short distance into the water. This wall intercepts and
slows the longshore current on the upcurrent side of the structure,
causing deposition of sand at that locality (Figure 19.39).
Figure 19.37 Sea walls.
This sea wall (arrow) at Palm Beach,
Florida, protects a hotel complex from coastal erosion. Structures
like this armor much of the shore in southeastern Florida.
Beach Nourishment
One of the primary reasons so many
people like coastlines is that they are attracted to the beach and
all the recreational and leisure opportunities it provides. Much
economic activity is directly tied to beaches, through either
tourism or the many people who live there. Given these impor-
tant relationships, people have a strong desire to maintain the
physical integrity of their particular beach, whether it fronts a
luxury hotel, condominiums, or a row of homes.
However, this desire to maintain an attractive beach is frequently
at odds with natural coastal processes because beaches often consist
of unconsolidated sands that are easily eroded. In an effort to offset
coastal erosion, many communities have organized beach nourish-
ment programs that bring in more sand to replace sand that is lost.
Groin
A short, low wall built at a right angle to the coast that
intercepts the longshore current.
Sea wall
Increased
erosion
along shore
Increased
erosion
along
shore
Wave
refraction
Figure 19.39 Groins and shoreline processes.
Groins such
as these along Lake Michigan in Chicago are walls built perpen-
dicular to the shore. These walls intercept the longshore current,
causing deposition of sand on the upcurrent side and erosion on
the downcurrent side of the structure. In Lake Michigan, the pre-
vailing longshore current flows from north (at the top of the photo)
to south. Note how sand has accumulated on the north side of
these groins and has washed away on the south side.
Figure 19.38 Beach walls and coastal erosion.
Although sea
walls protect the property they front from erosion, they cause
extensive erosion up and down shore because wave power is
deflected.
