propagations (the nonlinear interaction of tidal motion and
bathymetry), direct (localized) wind forcing, indirect
(large-scale) wind forcing, surface waves, and horizontal
and vertical density gradients (Prandle, 2009).
Measurements and analysis
Because water motions occur on a continuum time of
scale, it is critical to choose the appropriate time
duration over which to estimate residual circulations
(Kjerfve, 1989). In this case, the residual circulation will
depend on the averaging time scale used. In physical
oceanography analysis, there are several mathematical
filters that can be used to separate the nontidal currents
(due to wind forcing) into specific frequency bands.
In estuaries, as most of the current variability usually
occurs with a tidal periodicity, the residual circulation is
usually calculated as the residual water movement after
the currents is averaged over one, two, or numerous
complete tidal cycles (Kjerfve, 1979).
Bibliography
Kjerfve, B., 1979. Measurement and analysis of water current, temperature, salinity, and density. In Dyer, K. R. (ed.), Hydrography
and Sedimentation in Estuaries. Cambridge: Cambridge
University Press, pp. 186–216.
Kjerfve, B., 1989. Estuarine geomorphology and physical oceanography. In Day, J. W., Jr., Hall, C. A. S., Kemp, W. M., and YáñezArancibia, A. (eds.), Estuarine Ecology. New York: John Wiley
and Sons, pp. 47–78.
Prandle, D., 2009. Estuaries: Dynamics, Mixing, Sedimentation and
Morphology. Cambridge: Cambridge University Press.
REVETMENTS
Harry C. Friebel
U.S. Army Corps of Engineers, Philadelphia District,
CENAP-EC-EH, Philadelphia, PA, USA
Synonyms
Retaining wall
Definition
Revetments are a cover or facing of erosion-resistant
material placed directly on an existing slope, bank, scarp,
embankment, or dike to protect the adjacent shoreline and
upland areas against scour caused by waves and currents
(CHL, 2013).
Revetments consist of an armor layer, filter, and toe
protection, and they depend on the underlying soil for
support. Armor stone (high-energy environments) or riprap stone (lower-energy environments) must resist waves
and settlement and provide drainage to ensure stability.
The filter layer (e.g., smaller stone and geotextile fabrics)
supports the armor stone and prevents retained soil from
eroding through the armor layer by waves or groundwater
seepage. Toe protection prevents scour and displacement
of the seaward edge of the revetment. Revetments may
increase erosion immediately seaward and adjacent to
the structure (flanking) due to wave reflection while offering no protection to adjacent areas (USACE, 1981).
Revetments should be built high enough or with an apron
to prevent erosion at the top caused by wave run-up and
overtopping.
Bibliography
Coastal and Hydraulics Laboratory (CHL), (2013). U.S. Army
Corps of Engineers. U.S. Department of Defense. Available at
http://chl.erdc.usace.army.mil/glossary. Accessed 22 April 2013.
U.S. Army Corps of Engineers (USACE), 1981. Low Cost Shore
Protection: Final Report on the Shoreline Erosion Control Demonstration Program. Washington, DC: Office of the Chief of
Engineers.
Cross-references
Bulkheads
RHODOLITH/MAERL
Rafael Riosmena-Rodriguez
1 , Viviana Peña-Freire
2
,
Daniela Basso
3
, Nestor M. Robinson
1 and
Gustavo Hinojosa-Arango
4
1
Programa de Investigación en Botãnica Marina,
Departamento Académico de Biología Marina,
Universidad Autónoma de Baja California Sur, La Paz,
Baja California Sur, Mexico
2
Laboratorio de Algas Marinas, Departamento de
Biología Animal Biología Vegetal y Ecología,
Universidade da Coruña, A Coruña, Spain
3
Università degli Studi di Milano-Bicocca, Milano, Italy
4
Centro para la Biodiversidad Marina y la Conservacion,
La Paz, BCS, Mexico
Synonyms
Boxwork rhodolith; Coralline algal nodules; Maerl;
Nucleated rhodoliths; Oncolith/oncoid; Prâlines; Rhodoid
Definition
Rhodolith/maerl is the most common term used for free
living coralline red algae which live on sediments
(Steller et al., 2003).
Description
The term rhodolith literally means “red stone” (Bosence,
1983a) and consists of the ancient Greek words for
504
REVETMENTS
bathymetry), direct (localized) wind forcing, indirect
(large-scale) wind forcing, surface waves, and horizontal
and vertical density gradients (Prandle, 2009).
Measurements and analysis
Because water motions occur on a continuum time of
scale, it is critical to choose the appropriate time
duration over which to estimate residual circulations
(Kjerfve, 1989). In this case, the residual circulation will
depend on the averaging time scale used. In physical
oceanography analysis, there are several mathematical
filters that can be used to separate the nontidal currents
(due to wind forcing) into specific frequency bands.
In estuaries, as most of the current variability usually
occurs with a tidal periodicity, the residual circulation is
usually calculated as the residual water movement after
the currents is averaged over one, two, or numerous
complete tidal cycles (Kjerfve, 1979).
Bibliography
Kjerfve, B., 1979. Measurement and analysis of water current, temperature, salinity, and density. In Dyer, K. R. (ed.), Hydrography
and Sedimentation in Estuaries. Cambridge: Cambridge
University Press, pp. 186–216.
Kjerfve, B., 1989. Estuarine geomorphology and physical oceanography. In Day, J. W., Jr., Hall, C. A. S., Kemp, W. M., and YáñezArancibia, A. (eds.), Estuarine Ecology. New York: John Wiley
and Sons, pp. 47–78.
Prandle, D., 2009. Estuaries: Dynamics, Mixing, Sedimentation and
Morphology. Cambridge: Cambridge University Press.
REVETMENTS
Harry C. Friebel
U.S. Army Corps of Engineers, Philadelphia District,
CENAP-EC-EH, Philadelphia, PA, USA
Synonyms
Retaining wall
Definition
Revetments are a cover or facing of erosion-resistant
material placed directly on an existing slope, bank, scarp,
embankment, or dike to protect the adjacent shoreline and
upland areas against scour caused by waves and currents
(CHL, 2013).
Revetments consist of an armor layer, filter, and toe
protection, and they depend on the underlying soil for
support. Armor stone (high-energy environments) or riprap stone (lower-energy environments) must resist waves
and settlement and provide drainage to ensure stability.
The filter layer (e.g., smaller stone and geotextile fabrics)
supports the armor stone and prevents retained soil from
eroding through the armor layer by waves or groundwater
seepage. Toe protection prevents scour and displacement
of the seaward edge of the revetment. Revetments may
increase erosion immediately seaward and adjacent to
the structure (flanking) due to wave reflection while offering no protection to adjacent areas (USACE, 1981).
Revetments should be built high enough or with an apron
to prevent erosion at the top caused by wave run-up and
overtopping.
Bibliography
Coastal and Hydraulics Laboratory (CHL), (2013). U.S. Army
Corps of Engineers. U.S. Department of Defense. Available at
http://chl.erdc.usace.army.mil/glossary. Accessed 22 April 2013.
U.S. Army Corps of Engineers (USACE), 1981. Low Cost Shore
Protection: Final Report on the Shoreline Erosion Control Demonstration Program. Washington, DC: Office of the Chief of
Engineers.
Cross-references
Bulkheads
RHODOLITH/MAERL
Rafael Riosmena-Rodriguez
1 , Viviana Peña-Freire
2
,
Daniela Basso
3
, Nestor M. Robinson
1 and
Gustavo Hinojosa-Arango
4
1
Programa de Investigación en Botãnica Marina,
Departamento Académico de Biología Marina,
Universidad Autónoma de Baja California Sur, La Paz,
Baja California Sur, Mexico
2
Laboratorio de Algas Marinas, Departamento de
Biología Animal Biología Vegetal y Ecología,
Universidade da Coruña, A Coruña, Spain
3
Università degli Studi di Milano-Bicocca, Milano, Italy
4
Centro para la Biodiversidad Marina y la Conservacion,
La Paz, BCS, Mexico
Synonyms
Boxwork rhodolith; Coralline algal nodules; Maerl;
Nucleated rhodoliths; Oncolith/oncoid; Prâlines; Rhodoid
Definition
Rhodolith/maerl is the most common term used for free
living coralline red algae which live on sediments
(Steller et al., 2003).
Description
The term rhodolith literally means “red stone” (Bosence,
1983a) and consists of the ancient Greek words for
504
REVETMENTS