A guide for planners and managers - IUCN

234 MARINE AND COASTAL
PROTECTED AREAS
Photo by N.W. Pammenter.
Variation in foreshore slope from one region to another appears to be related
to mean nearshore wave heights—the gentler slopes occur on coasts with higher waves.
The inverse relation between slope and wave height is partly caused by the relative
frequency of the steep or high eroding waves which produce gentle foreshore slopes
and the low accretionary post-storm waves which produce steeper beaches (COE, 1984).
In summary:
– Slope of the foreshore on open sand beaches depends principally on size of the
sand grains and (to a lesser extent) on nearshore wave height.
– Slope of the foreshore tends to increase with increasing median grain size.
– Slope of the foreshore tends to decrease with increasing wave height.
FIGURE II-43.
Outlet of a typical bar-built estuary (Umhlanga Nature Reserve, South
Africa) which alternately opens and closes.
4.3 Beach Protection
Natural channels through
the beach may require special
attention. Such channels may
be permanent, allowing daily
tidal flow, or temporary, allowing
drainage of land runoff water
during flooding periods (Figure
II-43). Such channels often move
laterally along the beach as a
natural response to the forces
of the sea or the runoff flow.
Attempts are often made to fix
the position and depth of such
inlets to facilitate boat traffic.
The natural forces at work are immense, making stabilization of beaches a difficult
and often elusive endeavor. It is usually much better to not intervene with engineering
works and to let nature prevail. Then, management may be needed to maintain the
beach profile by protecting the natural processes that supply the beach with sand as
well as the sand-storage capacity of the beach elements themselves.
It must be remembered that the key to the natural protection provided by the
beachfront is the sand, which is held in storage and yielded to storm waves, thereby
dissipating the force of their attack. Consequently, taking sand from any part of the
beach—dry beach, wet beach, bar or the nearshore submerged zone—can lead to erosion
and recession of the beachfront. Therefore, beach conservation should start with the
premise that any removal of sand is adverse, whether for construction fill, concrete
aggregate, or any other purpose, and should be prohibited or tightly controlled.