Sometimes structures must be provided to protect dunes, to maintain
a spécifie beach dimension, or to reduce nourishment requirements. In
each case, the cost of such structures must be weighed against the benefits they would provide. Thus, measures to provide and keep a wider protective and recreational beach for a short section of an eroding shore
would require excessive nourishment without supplémentai structures such
as groins to reduce the rate of los.s of -material from the widened beach.
A long, high terminal groin or jetty is frequently justified at the downdrift end of a beach restoration project to reduce losses of fill into an
inlet and to stabilize the lip of the inlet.
1.6 CONSERVATION OF SAND
Expérience and study hâve demonstrated that sand from dunes, beaches,
and nearshore areas is the best material availabié naturally in suitable
form to protect shores. Where sand is available in abondant quantifies,
protective measures are greatly simplified and reduced in cost. When
dunes and broad, gently sloping beaches can no longer be provided, it is
necessary to resort to alternative structures, and the recreational attraction of the seashore is lost or greatly diminished.
Sand is a diminishing natural resource. Sand was once available to
our shores in adéquate supply from streams, rivers and glaciers, and by
Coastal érosion. Now cultural development in the watershed areas and along
previously eroding shores has progressed to a stage where large areas of
our coast now receive little or no sand through natural geological processes. Continued cultural development in both inland and shore areas
tends to further reduce Coastal érosion with resulting réduction in sand
supply to the shore. It thus becomes apparent that sand must be conserved.
This does not mean local hoarding of beach sand at the expense of adjoining areas, but rather the élimination of wasteful practices and the prévention of losses from the shore zone whenever feasible.
Fortunately, nature has provided extensive stores of beach sand in
bays, lagoons, estuaries and offshore areas that can be used as a source
of beach and dune replenishment where the ecological balance will not be
disruptedo Massive dune deposits are also available at some locations,
though these must be used with caution to avoid exposing the area to flood
hazard. These sources are not always located in the proper places for
économie utilization, nor will they last forever. When they are gone, we
must face increasing costs for the préservation of our shores. Offshore
sand deposits will probably become the most important source in the future.
Mechanical bypassing of sand at Coastal inlets is one means of conservation that will corne into increasing practice. Mining of beach sand for
commercial purposes, formerly a common procedure, is rapidly being reduced
as Coastal communities learn the need for regulating this practice. Modem
hopper dredges, used for channel maintenance in Coastal inlets, are being
equipped with a pump-out capability so their loads can be discharged near
the shore instead of being dumped at sea. On the California coast, where
large volumes of sand are lost into deep submarine canyons near the shore,
1-21
a spécifie beach dimension, or to reduce nourishment requirements. In
each case, the cost of such structures must be weighed against the benefits they would provide. Thus, measures to provide and keep a wider protective and recreational beach for a short section of an eroding shore
would require excessive nourishment without supplémentai structures such
as groins to reduce the rate of los.s of -material from the widened beach.
A long, high terminal groin or jetty is frequently justified at the downdrift end of a beach restoration project to reduce losses of fill into an
inlet and to stabilize the lip of the inlet.
1.6 CONSERVATION OF SAND
Expérience and study hâve demonstrated that sand from dunes, beaches,
and nearshore areas is the best material availabié naturally in suitable
form to protect shores. Where sand is available in abondant quantifies,
protective measures are greatly simplified and reduced in cost. When
dunes and broad, gently sloping beaches can no longer be provided, it is
necessary to resort to alternative structures, and the recreational attraction of the seashore is lost or greatly diminished.
Sand is a diminishing natural resource. Sand was once available to
our shores in adéquate supply from streams, rivers and glaciers, and by
Coastal érosion. Now cultural development in the watershed areas and along
previously eroding shores has progressed to a stage where large areas of
our coast now receive little or no sand through natural geological processes. Continued cultural development in both inland and shore areas
tends to further reduce Coastal érosion with resulting réduction in sand
supply to the shore. It thus becomes apparent that sand must be conserved.
This does not mean local hoarding of beach sand at the expense of adjoining areas, but rather the élimination of wasteful practices and the prévention of losses from the shore zone whenever feasible.
Fortunately, nature has provided extensive stores of beach sand in
bays, lagoons, estuaries and offshore areas that can be used as a source
of beach and dune replenishment where the ecological balance will not be
disruptedo Massive dune deposits are also available at some locations,
though these must be used with caution to avoid exposing the area to flood
hazard. These sources are not always located in the proper places for
économie utilization, nor will they last forever. When they are gone, we
must face increasing costs for the préservation of our shores. Offshore
sand deposits will probably become the most important source in the future.
Mechanical bypassing of sand at Coastal inlets is one means of conservation that will corne into increasing practice. Mining of beach sand for
commercial purposes, formerly a common procedure, is rapidly being reduced
as Coastal communities learn the need for regulating this practice. Modem
hopper dredges, used for channel maintenance in Coastal inlets, are being
equipped with a pump-out capability so their loads can be discharged near
the shore instead of being dumped at sea. On the California coast, where
large volumes of sand are lost into deep submarine canyons near the shore,
1-21