A guide for planners and managers - IUCN

4. Backshore. The part of the
beach that is usually dry and
that lies between the foreshore
and the dunes, and that
is acted upon by waves only
during storms and exceptionally
high water.
5. Dunes. More or less continuous
mounds of loose, windblown
material, usually sand,
behind the berm (often
vegetated). The first tier dune
is termed the “foredune,” or
the “frontal” or “primary”
dune; those behind the frontal
dune are called “secondary,”
“rear,” or “back” dunes. An
PART II
Protected Areas for Beaches
active dune is one that is mobile, or in the process of visibly gaining or losing sand;
such a dune is usually vegetated mostly with grasses rather than woody vegetation.
Two other terms that need definition are:
FIGURE II-42.
Sand and coral blocks have been mined from the offshore bars of
the Rodney Bay beach in St. Lucia. The only solution is artificial sand
replenishment because storm waves have eroded this tourist beach.
Pigeon Island National Historic Park is visible in the background.
1. Berm. A ridge or ridges on the backshore of the beach, formed by the deposit of
material by wave action, that marks the upper limit of ordinary high tides and wave
wash; berms often have sharply sloping leading edges.
2. Beach ridge. A more or less continuous mound of beach material behind the berm
that has been heaped up by wave action during extreme high-water levels; if
largely wind built, the ridge is usually termed a “dune,” and often is vegetated.
Under storm attack the dynamic response of a beach is to sacrifice some of the
beach, and often the foredune, to provide material to an offshore bar. This bar helps
to protect the shoreline from further erosion. After a storm or storm season, natural
defenses may again be re-formed by normal wave and wind action. Following a
storm there is a return to more normal conditions, which are dominated by low, long
swells. These waves transport sand from the offshore bar, built during the storm, and
place the material on the beach. Winds then transport the sand onto the dunes where
it is trapped by the vegetation. The rebuilding process takes much longer than the
short time span during which the erosion took place.
It is important to realize that the erosional and depositional cycles of beaches
may respond to forces acting far from the beach itself. Of special importance are sources
such as offshore shoals and currents, inland dune systems, and river outflows that
bring sand to the sea.
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Photo by Erkki Siirila.