4.736 Déflation. The loose sand that forms beaches is available to be
transported by wind. After a storm, shells and other objects are often
found perched on pedestals of sand left standing after the wind eroded
less protected sand in the neighborhood. Such érosion over the total
beach surface can amount to significant quantities. Unstabilized dunes
may form and migrate landward, resulting in an important net loss to the
littoral zone. Examples include some dunes along the Oregon coast (Cooper, 1958), between Pismo Beach and Point Arguello, California (Bowen
and Inman, 1966); central Padre Island (Watson, 1971); and near Cape Henlopen, Delaware (Kraft, 1971). Typical rates of transport due to wind
range from 1 to 10 cubic yards per year per foot of beach front where
wind transport is noticeable. (Cooper, 1958; Bowen and Inman, 1966;
Savage and Woodhouse, 1968; and Gage, 1970.) However average rates probably range from 1 to 3 cubic yards per year per foot.
The largest wind-transported losses are usually associated with
accreting beaches that provide a broad area of loose sand over a period
of years. Sand migrating inland from Ten Mile River Beach in the vicinity of Laguna Point, California, is shown in Figure 4-48.
Study of aerial photographs and field reconnaissance can easily
establish whether or not important losses or gains from wind transport
occur in a study area. However, detailed studies are usually required
to establish the importance of wind transport in the sédiment budget.
4.737 Carbonate Loss. The abrasion résistance of carbonate materials
is much lower than quartz, and the solubility of carbonate materials is
usually much greater than quartz. However, there is insufficient evidence
to show that significant quantities of carbonate sands are lost from the
littoral zone in the time scale of engineering interest through either
abrasion or solution.
4.738 Mining and Dredging. From ancient times, sand and gravel hâve
been mined along coasts. In some countries, for example Denmark and
England, mining has occasionally had undesirable effects on Coastal settlements in the vicinity. Sand mining in most places has been discouraged by
législation and the rising cost of Coastal land, but it still is locally
important. (Magoon, et al., 1972.) It is expected that mining will become
more important in the offshore area in the future. (Duane, 1968, and Fisher
1969.)
Such mining must be conducted far enough offshore so the mine pit
will not act as a sink for littoral materials, or refract waves adversely,
or substantially reduce the wave damping by bottom frictiori and percolation.
.
littoral zone when dredged from naviga
Material is also lost to the lit
littoral zone, and the
ble waters (channels and entrances) wit in
littoral zone,
dredged material is dumped in some area ou
jeep water offshore. This
These dump areas can be for land fil » or
-First costs for some
action has been a common practice, becaus
wav.
dredging operations are cheaper when one
4-129
transported by wind. After a storm, shells and other objects are often
found perched on pedestals of sand left standing after the wind eroded
less protected sand in the neighborhood. Such érosion over the total
beach surface can amount to significant quantities. Unstabilized dunes
may form and migrate landward, resulting in an important net loss to the
littoral zone. Examples include some dunes along the Oregon coast (Cooper, 1958), between Pismo Beach and Point Arguello, California (Bowen
and Inman, 1966); central Padre Island (Watson, 1971); and near Cape Henlopen, Delaware (Kraft, 1971). Typical rates of transport due to wind
range from 1 to 10 cubic yards per year per foot of beach front where
wind transport is noticeable. (Cooper, 1958; Bowen and Inman, 1966;
Savage and Woodhouse, 1968; and Gage, 1970.) However average rates probably range from 1 to 3 cubic yards per year per foot.
The largest wind-transported losses are usually associated with
accreting beaches that provide a broad area of loose sand over a period
of years. Sand migrating inland from Ten Mile River Beach in the vicinity of Laguna Point, California, is shown in Figure 4-48.
Study of aerial photographs and field reconnaissance can easily
establish whether or not important losses or gains from wind transport
occur in a study area. However, detailed studies are usually required
to establish the importance of wind transport in the sédiment budget.
4.737 Carbonate Loss. The abrasion résistance of carbonate materials
is much lower than quartz, and the solubility of carbonate materials is
usually much greater than quartz. However, there is insufficient evidence
to show that significant quantities of carbonate sands are lost from the
littoral zone in the time scale of engineering interest through either
abrasion or solution.
4.738 Mining and Dredging. From ancient times, sand and gravel hâve
been mined along coasts. In some countries, for example Denmark and
England, mining has occasionally had undesirable effects on Coastal settlements in the vicinity. Sand mining in most places has been discouraged by
législation and the rising cost of Coastal land, but it still is locally
important. (Magoon, et al., 1972.) It is expected that mining will become
more important in the offshore area in the future. (Duane, 1968, and Fisher
1969.)
Such mining must be conducted far enough offshore so the mine pit
will not act as a sink for littoral materials, or refract waves adversely,
or substantially reduce the wave damping by bottom frictiori and percolation.
.
littoral zone when dredged from naviga
Material is also lost to the lit
littoral zone, and the
ble waters (channels and entrances) wit in
littoral zone,
dredged material is dumped in some area ou
jeep water offshore. This
These dump areas can be for land fil » or
-First costs for some
action has been a common practice, becaus
wav.
dredging operations are cheaper when one
4-129