In order to develop a design to protect infrastructure or
restore an eroding shoreline, a coastal engineer must consider the site environment, available tools, customers, and
regulations.
Site environment
Before developing a design the project site is investigated.
Site characteristics of interest to a coastal engineer are:
• Sediment type (rock, gravel, sand, clay, or muddy soils)
and distribution of particle sizes and unit weights are
determined. Ideally core samples are taken along the
cross section of the shoreline. Sediments are classified
by the distribution of particle diameters; clays and
muddy soils are treated differently than sand or gravel
as their properties are affected by water (Healy et al.,
2000).
• Shoreline/beach equilibrium profile – what is the natural profile of the shoreline and are there historical
records showing how it has changed over time? Shorelines can be surveyed by LIDAR, aerial photography,
and field surveys to determine present conditions.
• Site topography and bathymetry – geographic maps and
charts provide general information. Surveys of the land
and shallow water areas can show the detailed topography of specific shoreline areas especially when the site
is changing rapidly.
• Sediment transport rates and direction – erosion and
accretion of shorelines in the site area, predominant
wave direction, and currents along with numerical
models of the site can contribute to sediment transport
rate estimates.
• Coastal inlets – the water flow in and out of inlets to
marinas/ports and inland waterways for the coastal population can severely affect the natural sediment processes in an area, and special considerations must be
used in their design or presence near a project site
(Kraus, 2005)
• Marine habitat – a site can have both native and invasive species of flora and fauna. How can the design
enhance the local habitat?
• Hydrodynamics – waves, ship wakes, currents, and
low-frequency motions: tides, seiches, and storm
surge – regional records of the magnitude, and frequency of atmospheric conditions, winds, waves, and
tides exist internationally. Coastal engineers can estimate winds, wave, tide, seiche, and storm water levels
from available site data. A major consideration is the
wind fetch or maximum distance that the wind blows
over the body of water and the angle of incidence to
the shoreline. Of particular concern is the prediction of
wave run-up and wave overtopping on the shoreline
(Jones et al., 2005). Wave run-up is the elevation above
the still water on a beach or structural slope due to tide,
surge, and wave setup. Wave overtopping is the volumetric rate at which run-up flows over the top or crest
of a slope of a beach, dune, or structure. Wave
diffraction, the bending of wave fronts around the ends
of coastal structures, must be considered.
• Weather and extreme events – hurricanes/cyclones,
tropical storms, earthquakes, and tsunamis – what are
the natural hazards in the site area? With increased
coastal populations, hazard maps have been developed
to show seismic, extreme wind and flooding and wave
inundation areas. Has a risk assessment been performed
for the site evaluating the vulnerability of the population to the hazards?
• Sea-level rise/subsidence – what is the forecast rate of
change of the mean sea-level? The rates of change of
sea-level and its causes are continuously documented
and updated by scientists (IPCC, 2014).
• Proximity/access to site – road, railway, marina, and
ports – how close is the site to major infrastructure?
Coastal shorelines naturally fluctuate over time. Is there
a room at the site to allow for fluctuation or does the
shoreline protection require a stationary profile to protect infrastructure?
Available tools
Design manuals
Design manuals exist to aid the coastal engineer in design
(USACE, 2002; CIRIA, 2007). These manuals detail
design guidance for all types of coastal structures. Within
these manuals, design methodologies are recommended.
Simple formulas and techniques based on empirical field
data or laboratory model tests are recommended for preliminary design estimates. The engineer must be familiar
with the assumptions made in these formulas to evaluate
their suitability for a site.
Numerical tools
When there are gaps in environmental site information,
numerical models have been developed to predict meteorological and oceanographic conditions, wave run-up,
and overtopping. Increasingly climate change/hazard risk
models are being developed for project sites. Coastal scientists and engineers must be familiar with how the
models operate and the assumptions used to develop them,
before applying them to an individual site design.
When field data of weather, oceanographic topography,
and bathymetric conditions exists for a location, the time
period of data recording should be compared to the proposed life of the structure. Trends can be forecast or
extrapolated using both statistics and modeling.
Physical modeling
For large coastal construction projects, physical model
testing can be performed on a scaled model of the design.
Coastal model testing techniques are provided in detail
(Hughes, 1993). Model tests can confirm and enhance
numerical predictions. They are also used when the design
is too complicated for a numerical model.
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COASTAL ENGINEERING
restore an eroding shoreline, a coastal engineer must consider the site environment, available tools, customers, and
regulations.
Site environment
Before developing a design the project site is investigated.
Site characteristics of interest to a coastal engineer are:
• Sediment type (rock, gravel, sand, clay, or muddy soils)
and distribution of particle sizes and unit weights are
determined. Ideally core samples are taken along the
cross section of the shoreline. Sediments are classified
by the distribution of particle diameters; clays and
muddy soils are treated differently than sand or gravel
as their properties are affected by water (Healy et al.,
2000).
• Shoreline/beach equilibrium profile – what is the natural profile of the shoreline and are there historical
records showing how it has changed over time? Shorelines can be surveyed by LIDAR, aerial photography,
and field surveys to determine present conditions.
• Site topography and bathymetry – geographic maps and
charts provide general information. Surveys of the land
and shallow water areas can show the detailed topography of specific shoreline areas especially when the site
is changing rapidly.
• Sediment transport rates and direction – erosion and
accretion of shorelines in the site area, predominant
wave direction, and currents along with numerical
models of the site can contribute to sediment transport
rate estimates.
• Coastal inlets – the water flow in and out of inlets to
marinas/ports and inland waterways for the coastal population can severely affect the natural sediment processes in an area, and special considerations must be
used in their design or presence near a project site
(Kraus, 2005)
• Marine habitat – a site can have both native and invasive species of flora and fauna. How can the design
enhance the local habitat?
• Hydrodynamics – waves, ship wakes, currents, and
low-frequency motions: tides, seiches, and storm
surge – regional records of the magnitude, and frequency of atmospheric conditions, winds, waves, and
tides exist internationally. Coastal engineers can estimate winds, wave, tide, seiche, and storm water levels
from available site data. A major consideration is the
wind fetch or maximum distance that the wind blows
over the body of water and the angle of incidence to
the shoreline. Of particular concern is the prediction of
wave run-up and wave overtopping on the shoreline
(Jones et al., 2005). Wave run-up is the elevation above
the still water on a beach or structural slope due to tide,
surge, and wave setup. Wave overtopping is the volumetric rate at which run-up flows over the top or crest
of a slope of a beach, dune, or structure. Wave
diffraction, the bending of wave fronts around the ends
of coastal structures, must be considered.
• Weather and extreme events – hurricanes/cyclones,
tropical storms, earthquakes, and tsunamis – what are
the natural hazards in the site area? With increased
coastal populations, hazard maps have been developed
to show seismic, extreme wind and flooding and wave
inundation areas. Has a risk assessment been performed
for the site evaluating the vulnerability of the population to the hazards?
• Sea-level rise/subsidence – what is the forecast rate of
change of the mean sea-level? The rates of change of
sea-level and its causes are continuously documented
and updated by scientists (IPCC, 2014).
• Proximity/access to site – road, railway, marina, and
ports – how close is the site to major infrastructure?
Coastal shorelines naturally fluctuate over time. Is there
a room at the site to allow for fluctuation or does the
shoreline protection require a stationary profile to protect infrastructure?
Available tools
Design manuals
Design manuals exist to aid the coastal engineer in design
(USACE, 2002; CIRIA, 2007). These manuals detail
design guidance for all types of coastal structures. Within
these manuals, design methodologies are recommended.
Simple formulas and techniques based on empirical field
data or laboratory model tests are recommended for preliminary design estimates. The engineer must be familiar
with the assumptions made in these formulas to evaluate
their suitability for a site.
Numerical tools
When there are gaps in environmental site information,
numerical models have been developed to predict meteorological and oceanographic conditions, wave run-up,
and overtopping. Increasingly climate change/hazard risk
models are being developed for project sites. Coastal scientists and engineers must be familiar with how the
models operate and the assumptions used to develop them,
before applying them to an individual site design.
When field data of weather, oceanographic topography,
and bathymetric conditions exists for a location, the time
period of data recording should be compared to the proposed life of the structure. Trends can be forecast or
extrapolated using both statistics and modeling.
Physical modeling
For large coastal construction projects, physical model
testing can be performed on a scaled model of the design.
Coastal model testing techniques are provided in detail
(Hughes, 1993). Model tests can confirm and enhance
numerical predictions. They are also used when the design
is too complicated for a numerical model.
100
COASTAL ENGINEERING