BARRIER SPITS
Wenyan Zhang
MARUM - Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Synonyms
Barrier; Spits
Definition
Barrier spits are long narrow strips of depositional bodies
emerging from water (Evans, 1942), with one end attached
to a coast that serves as the source of sediment supply
(proximal end) and the other end jutting into open water
(distal end), forming a shelter for its inner water.
Introduction
Offshore waves normally approach the surf zone of a coast
in an oblique angle. A combination of shore-oblique
swash caused by the incoming waves and shore-normal
backwash caused by gravity creates a longshore drift,
which is further strengthened by longshore currents generated by wave breaking. Sediment is entrained by strong
turbulence induced by wave breaking and transported
down-drift along the coastline by longshore currents.
Longshore sediment transport rate remains constant if
there exists a uniformity of waves and nearshore isobaths
along the coastline (USACE, 1984). Net deposition occurs
where the longshore uniformity is broken by a decrease of
the wave energy. This is normally caused by a deepening
of the bathymetry or a change of the coastline orientation.
In the latter case, the boundary constraint of the longshore
currents by the coastline no longer exists, and the currents
are veered by a barotropic pressure induced by the wave
radiation stress. On the side to which the currents are
veered, turbulence is dissipated by free calm water and
no longer able to entrain the full load. Much of the sediment is deposited as a result, forming a submerged bar.
This submerged bar subsequently acts to maintain the original direction of the longshore currents and on the other
hand serves as a reservoir for sediment deposit. Deposition
on the submerged bar will not stop until a uniformity of
waves and nearshore isobaths is again built up. Eventually
an above-water spit is developed and elongated by this
process. Terrestrial onshore aeolian transport, which
builds up foredunes on the berm of the newly formed
beach, plays a key role in stabilizing the spit and allows
a further development of the spit. The spit becomes
a barrier spit when it is long enough to provide a shelter
for its inner water. As foredunes are a common feature
on a barrier spit, they serve as useful records for historical
environmental change (Tamura, 2012).
Three basic preconditions have to be fulfilled for the
formation of a barrier spit:
1. A littoral drift to provide continuous sediment supply
2. A change in the coastline orientation (i.e., a turning
point) that is significant enough to remove the boundary constraint of the longshore currents
3. A weak offshore transport at the turning point to enable
a major part of the deposited sediment remaining
on-site.
Bibliography
Evans, O. F., 1942. The origin of spits, bars and related structures.
Journal of Geology, 50, 846–863.
Tamura, T., 2012. Beach ridges and prograded beach deposits as
palaeoenvironment records. Earth-Science Reviews, 114,
279–297.
U.S. Army Corps of Engineers, 1984. Shore Protection Manual,
4th edn. Washington, DC: Department of the Army, U.S. Corps
of Engineers.
BEACH MANAGEMENT
Mafalda Marques Carapuço
Institute Dom Luiz, University of Lisbon, Campo Grande,
Lisbon, Portugal
Definition
Beach management is the act of organizing and coordinating efforts to identify and implement the optimal use of
means to accomplish an end for a specific beach.
Introduction
The process of managing implies the existence of objectives and is used as a technique for achieving an end.
Managing also implies knowing the system being investigated, and this constitutes a tremendous challenge in
highly dynamic systems, such as a beach, one of the most
mutable environments in the world, where morphologic
variations can occur on time scales from a few seconds
to thousands of years and more and on space scales from
meters – or even less – to thousands of kilometers.
In any management activity, four steps are mandatory:
plan, do, check, and act (approach known as the PDCA
or Deming cycle). Plan implies the establishment of management objectives, do corresponds to the implementation
of the objectives, check implies to the objectives
implemented and compare them against the expected
results (targets or goals from the plan) to ascertain the
differences, and act may imply corrective actions on
differences between actual and planned results.
In beach management, the same approach should be
considered with the necessary adaptations due to the particularities of the beach environment. In fact, the beach
management approaches described in the literature are,
in general, implicit deviations of the PDCA cycle
(e.g., Micallef and Williams, 2002; Drake, 2010).
BEACH MANAGEMENT
53
Wenyan Zhang
MARUM - Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Synonyms
Barrier; Spits
Definition
Barrier spits are long narrow strips of depositional bodies
emerging from water (Evans, 1942), with one end attached
to a coast that serves as the source of sediment supply
(proximal end) and the other end jutting into open water
(distal end), forming a shelter for its inner water.
Introduction
Offshore waves normally approach the surf zone of a coast
in an oblique angle. A combination of shore-oblique
swash caused by the incoming waves and shore-normal
backwash caused by gravity creates a longshore drift,
which is further strengthened by longshore currents generated by wave breaking. Sediment is entrained by strong
turbulence induced by wave breaking and transported
down-drift along the coastline by longshore currents.
Longshore sediment transport rate remains constant if
there exists a uniformity of waves and nearshore isobaths
along the coastline (USACE, 1984). Net deposition occurs
where the longshore uniformity is broken by a decrease of
the wave energy. This is normally caused by a deepening
of the bathymetry or a change of the coastline orientation.
In the latter case, the boundary constraint of the longshore
currents by the coastline no longer exists, and the currents
are veered by a barotropic pressure induced by the wave
radiation stress. On the side to which the currents are
veered, turbulence is dissipated by free calm water and
no longer able to entrain the full load. Much of the sediment is deposited as a result, forming a submerged bar.
This submerged bar subsequently acts to maintain the original direction of the longshore currents and on the other
hand serves as a reservoir for sediment deposit. Deposition
on the submerged bar will not stop until a uniformity of
waves and nearshore isobaths is again built up. Eventually
an above-water spit is developed and elongated by this
process. Terrestrial onshore aeolian transport, which
builds up foredunes on the berm of the newly formed
beach, plays a key role in stabilizing the spit and allows
a further development of the spit. The spit becomes
a barrier spit when it is long enough to provide a shelter
for its inner water. As foredunes are a common feature
on a barrier spit, they serve as useful records for historical
environmental change (Tamura, 2012).
Three basic preconditions have to be fulfilled for the
formation of a barrier spit:
1. A littoral drift to provide continuous sediment supply
2. A change in the coastline orientation (i.e., a turning
point) that is significant enough to remove the boundary constraint of the longshore currents
3. A weak offshore transport at the turning point to enable
a major part of the deposited sediment remaining
on-site.
Bibliography
Evans, O. F., 1942. The origin of spits, bars and related structures.
Journal of Geology, 50, 846–863.
Tamura, T., 2012. Beach ridges and prograded beach deposits as
palaeoenvironment records. Earth-Science Reviews, 114,
279–297.
U.S. Army Corps of Engineers, 1984. Shore Protection Manual,
4th edn. Washington, DC: Department of the Army, U.S. Corps
of Engineers.
BEACH MANAGEMENT
Mafalda Marques Carapuço
Institute Dom Luiz, University of Lisbon, Campo Grande,
Lisbon, Portugal
Definition
Beach management is the act of organizing and coordinating efforts to identify and implement the optimal use of
means to accomplish an end for a specific beach.
Introduction
The process of managing implies the existence of objectives and is used as a technique for achieving an end.
Managing also implies knowing the system being investigated, and this constitutes a tremendous challenge in
highly dynamic systems, such as a beach, one of the most
mutable environments in the world, where morphologic
variations can occur on time scales from a few seconds
to thousands of years and more and on space scales from
meters – or even less – to thousands of kilometers.
In any management activity, four steps are mandatory:
plan, do, check, and act (approach known as the PDCA
or Deming cycle). Plan implies the establishment of management objectives, do corresponds to the implementation
of the objectives, check implies to the objectives
implemented and compare them against the expected
results (targets or goals from the plan) to ascertain the
differences, and act may imply corrective actions on
differences between actual and planned results.
In beach management, the same approach should be
considered with the necessary adaptations due to the particularities of the beach environment. In fact, the beach
management approaches described in the literature are,
in general, implicit deviations of the PDCA cycle
(e.g., Micallef and Williams, 2002; Drake, 2010).
BEACH MANAGEMENT
53