EM 1110-2-1100 (Part I)
30 Apr 02
Chapter I-2
Coastal Diversity
I-2-1. Introduction
The coasts, or shores, of the world are the margins separating the 29 per cent of the earth that is land from
the 71 percent that is water. By reworking and often eroding the margins of the land, the seas aid streams,
subsurface water, glaciers, and the wind in wearing down the continents. Sediments derived from the land
are often transient along the coasts, temporarily forming beaches, bars or islands before coming to rest on the
sea floor. There is significant natural diversity in shore types throughout the United States and even greater
diversity throughout the world (see Part IV for details). Consequently, engineering, development, and policy
strategies need to be tailored for each unique region and need to be flexible to changes in the local condition.
Coastal engineers, managers, and planners need to be aware of coastal diversity for a number of reasons:
a. The coast is dynamic and constantly evolving to a new condition.
b. The balance and interaction of processes are different in different areas - understanding diversity
provides clues to the critical factors that may affect a particular study site.
c. Different settings imply different erosion and accretion sediment patterns.
d. Analytical tools and procedures may be suitable for a particular setting but totally inappropriate for
another.
e. Similarly, engineering solutions may only be appropriate for certain settings where they will function
properly.
Shorelines are subject to a broad range of processes, geology, morphology, and land usages. Although winds,
waves, water levels, tides, and currents affect all coasts, they vary in intensity and relative significance from
one location to another. Variations in sediment supply and geological setting add to this coastal diversity.
A more detailed discussion and analysis of the processes at work along the United States coasts is given by
Francis P. Shepard and Harold R. Wanless in their book Our Changing Coastline (1971).
I-2-2. Coastal Areas
The popular image of a long, straight, sandy beach with a sandy backshore and foreshore, vegetated sand
dunes, and gently sloping near shore zone with rhythmic plunging breakers may be the ideal image of the
zone where the land meets the sea, but is not the norm along most coasts. Not all coastal areas are sandy, nor
are all shores dominated by wave action. Some coastal areas have scenic clay bluffs or rocky headlands.
Others are shallow mud flats or lush wetlands. For some shores, tidal currents or river discharge dominate
sediment transport and the shore character. For other shores, the effects of glaciers, marine life (coral), or
volcanoes may control the geomorphology. Shore materials include transportable muds, silts, sands, shells,
gravels, and cobbles, and insitu rock formations or bedrock (erosive and non-erosive). In portions of the
United States, the coastal area is sinking and gradually becoming permanently inundated; in other areas, new
lands are accreting or even rising out of the sea.
a. Atlantic North: Glaciated coast (Figures I-2-1, I-2-2). These coasts are normally deeply indented
and bordered by numerous rocky islands. The embayments usually have straight sides and deep water as a
Coastal Diversity
I-2-1
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