Coastal Construction Manual - National Ready Mixed Concrete ...

IDENTIFYING HAZARDS 3
of the inlet in 1933 by a hurricane and construction of inlet jetties in 1934–1935 led to approximately
800 feet of accretion against the north jetty at Ocean City and approximately 1,700 feet of erosion on the
south side of the inlet along Assateague Island as of 1977 (Dean and Perlin 1977). Between 1976 and 1980,
shoreline change rates on Assateague Island averaged from 49 feet per year and -33 feet per year (USACE
2009b). In 2004, USACE began the “Long-Term Sand Management” project to restore Assateague Island.
Erosion and accretion patterns at stabilized inlets and
entrances sometimes differ from the classic pattern occurring
at the Ocean City Inlet. In some instances, accretion occurs
immediately adjacent to both jetties, with erosion beyond. In
some instances, erosion and accretion patterns near a stabilized
inlet change over time. Figure 3-42 shows buildings at Ocean
Shores, WA, that were threatened by shore erosion shortly
after their construction, despite the fact that the buildings
were located near an inlet jetty on a beach that was historically
viewed as accretional.
Development in the vicinity of a tidal inlet or bay, harbor,
or river entrance is often affected by lateral migration of the
channel and associated changes in sand bars (which may
focus waves and erosion on particular shoreline areas). Often,
these changes are cyclic in nature and can be identified and
forecast through a review of historical aerial photographs and
bathymetric data. Those considering a building site near a tidal
inlet or a bay, harbor, or river entrance should investigate the
history of the connection, associated shoreline fluctuations,
migration trends, and impacts of any stabilization structures.
Failure to do so could result in increased building vulnerability
or building loss to future shoreline changes.
NOTE
Cursory characterizations of
shoreline behavior in the vicinity
of a stabilized inlet, harbor, or
bay entrance should be rejected
in favor of a more detailed
evaluation of shoreline changes
and trends.
WARNING
Many State and local siting
regulations allow residential
development in areas where
erosion is likely to occur.
Designers should not assume that
a building sited in compliance
with minimum State and local
requirements is safe from future
erosion. See Chapter 4.
Figure 3‐42.
Buildings threatened by
erosion at Ocean Shores,
WA, in 1998. The rock
revetments were built in
response to shore erosion
along an area adjacent to
a jetty and thought to be
accretional
COASTAL CONSTRUCTION MANUAL
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