Shorelines and Shoreline Processes - The Changing Earth: Exploring Geology and Evolution - page 428

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Figure 16.20 Barrier Island Migration

Isle of
Wight Bay

Fenwick
Island

N

Lagoon Barrier island

a A barrier island. Ocean City

Jetty

Ocean City
Inlet

MARYLAND

Sea level
rise

Upper
Sinepuxent
Neck

Atlantic Ocean

Position of
shoreline

b A barrier island migrates landward as sea level rises and storm
waves carry sand from its seaward side into its lagoon.

1980
1849

Assateague
Island

0 2

1

Migrating
barrier island

Original
barrier island
position

Sea level
rise

km

Lagoon

d Jetties were constructed during the 1930s to protect the inlet at
Ocean City, Maryland, but they disrupted the net southerly longshore
drift and Assateague Island, starved of sediment, has migrated
500 m landward. Beginning in the fall of 2002, beach sand was
artifi cially replenished in an effort to stabilize the island.

Barrier island movement
c Over time, the entire island shifts toward the land.

being lost at a rate of about 90 km 2 per year. Much of this loss
results from sediment compaction, but rising sea level exacer-
bates the problem.
Another consequence of Hurricane Katrina was its ef-
fect on the Chandeleur Islands, off of Louisiana's southeast
coast (

Gulf Coasts, but would cover 20% of the entire country
of Bangladesh. Other problems associated with rising sea
level include increased coastal fl ooding during storms and
saltwater incursions that may threaten groundwater sup-
plies (see Chapter 13).
Armoring shorelines with seawalls (embankments
of reinforced concrete or stone) (Figure 16.18) and using
riprap (piles of stones,

Figure 16.21). These are barrier islands that ab-
sorb some of the impact of approaching storms, especially
storm surges. When Hurricane Katrina swept across this
area, the islands were battered and reduced to small shoals
(Figure 16.21).
Rising sea level also directly threatens many beaches
upon which communities depend for revenue. The beach
at Miami Beach, Florida, for instance, was disappearing
at an alarming rate until the Army Corps of Engineers
began replacing the eroded beach sand. The problem is
even more serious in other countries. A rise in sea level of
only 2 m would inundate large areas of the U.S. East and

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Figure 16.22a) protect beachfront
structures, but both are initially expensive and during large
storms are commonly damaged or destroyed. Seawalls do
afford some protection and are seen in many coastal areas
along the oceans and large lakes, but some states, includ-
ing North and South Carolina, Rhode Island, Oregon, and
Maine, no longer allow their construction. The futility of
artificially maintaining beaches is aptly shown by efforts
to protect homes on a South Carolina barrier island. After
each spring tide, heavy equipment builds a sand berm to

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