COASTAL EROSION CONTROL
Mena Ciarmiello and Michele Di Natale
DICDEA – Department of Civil Engineering, Design,
Building and Environment, Second University of Naples,
Aversa, Italy
Definitions
Coastal erosion is a natural or anthropogenic process in
which sediment is worn away from the shoreline and seafloor due to natural and anthropogenic factors, such as
storms, boat wakes, tidal currents, and rising sea levels.
Erosion control refers to erosion mitigation techniques
based on soft and hard structural shoreline stabilization
methods and nonstructural measures.
Hard structural stabilization refers to shoreline erosion
control approaches based on the construction of
man-made structures, such as seawalls, breakwaters, and
groins.
Soft structural stabilization refers to shoreline erosion
mitigation and control measures based on soft methods,
namely, sand, pebble, or gravel fill, such as beach
nourishment.
Nonstructural measures refer to any coastal erosion
control strategy that does not involve man-made construction or other physical measures, but is based on good practices, policies, and education aimed at reducing
anthropogenic and natural impacts, such as land use
restriction and zoning.
Introduction
Estuaries are transitional zones where marine and riverine
environments meet, i.e., where freshwater from a river
mixes with saltwater from the sea. Here, many habitats,
species, and ecological communities exist, and their ecosystem and naturalistic values are widely recognized.
Along coasts, river banks, and nearshore profiles are
governed by sediment transport equilibrium (i.e., erosion
and deposition phenomena). Alteration of this equilibrium
may result in shoreward recession, leading to land loss.
Since estuarine areas are often used for tourism and recreational purposes, this leads to financial loss as well as ecological community and biodiversity impairment. State and
local authorities thus aim to protect estuarine areas and to
mitigate erosion. A review of the causes of coastal erosion
and an evaluation of the erosion processes are provided
below, together with an analysis of erosion control
measures.
Causes of coastal erosion
There are many causes of coastal erosion processes attributable to natural and anthropogenic factors.
A classification can be based on the temporal scale of such
factors, distinguishing between short- and long-term
events. Natural processes consist of short-term events that
are generally the result of storms and river floods (i.e.,
high-energy content events), while long-term events relate
to sea-level rise (Pranzini and Rossi, 1995; Khalil, 1997),
tidal cycles, tectonic events, coastal subsidence (Khalil,
1997), climate change, river regimes, and discharge flux
(Medina and Lopez, 1997).
In regard to anthropogenic factors, sediment loss is generally due to medium- and long-term events, such as
decreasing sediment supply to coastal physiographic units
(Simeoni et al., 1997; Eronat, 1999; Loizidou and
Iacovou, 1999), deforestation in coastal and riverine
watersheds (Eronat, 1999), non-sustainable man-made
coastal structures and urban development (Fathallah and
Gueddari, 2001; Rakha and Abul-Azm, 2001), flow
regime and engineering structure changes, and riverbed
sand and gravel extraction (PAP/RAC, 2000).
Erosion processes
Suspension and bed load transport can be distinguished
(Fredsøe and Deigard, 1994), the latter mainly causing
the loss of grain size material on the seabed and affecting
long-term and short-term shoreline evolution. Such phenomena are primarily modeled by physical and mathematical and generally consider hydrodynamic and
morphological factors. Hydrodynamic models are based
on the classical equations of motion, with vertical averaged velocities (two-dimension models), and wave propagation, refraction, diffraction, and breaking. They evaluate
velocity flow fields under generic forcing (Figure 1).
Morphological models consider seabed characteristics
and evaluate bed load and shoreline evolution, for both
long-term and short-term conditions (Figure 2).
Physical models are based on two-dimensional and
three-dimensional laboratory scale similarity models that
use channels or large basins (Figure 3) to study both bed
load processes and evaluate the effectiveness of the structural design.
Finally, it should be pointed out that both physical and
mathematical models require a detailed knowledge of seabed morphology, waves and currents (i.e., river or tidal
currents or wave-generated currents), bathymetric surveys, and sediment characterization (pebble or sand
beaches, sediment grain size, and erodibilty changes).
Coastal erosion risk mitigation
A coastal erosion control project should be developed
with reference to coastal cells (Eurosion, 2004), which
are lengths of coastlines in which a complete sediment balance can be identified. Spatial and temporal erosion phenomena scales should also be identified. Acute and
structural erosion can be distinguished. Acute erosion is
connected to waves, wind, and tidal action and typically
covers temporal and spatial scales up to 1 month and from
about 1 m to 100 km, respectively. On the contrary, structural erosion involves larger temporal and spatial scales,
from about 1 month to 100 years and from 1 to
1,000 km, respectively (Safecoast, 2008).
Depending on spatial scale, coastal erosion control
measures can target (1) specific river bank sections and
COASTAL EROSION CONTROL
131
Mena Ciarmiello and Michele Di Natale
DICDEA – Department of Civil Engineering, Design,
Building and Environment, Second University of Naples,
Aversa, Italy
Definitions
Coastal erosion is a natural or anthropogenic process in
which sediment is worn away from the shoreline and seafloor due to natural and anthropogenic factors, such as
storms, boat wakes, tidal currents, and rising sea levels.
Erosion control refers to erosion mitigation techniques
based on soft and hard structural shoreline stabilization
methods and nonstructural measures.
Hard structural stabilization refers to shoreline erosion
control approaches based on the construction of
man-made structures, such as seawalls, breakwaters, and
groins.
Soft structural stabilization refers to shoreline erosion
mitigation and control measures based on soft methods,
namely, sand, pebble, or gravel fill, such as beach
nourishment.
Nonstructural measures refer to any coastal erosion
control strategy that does not involve man-made construction or other physical measures, but is based on good practices, policies, and education aimed at reducing
anthropogenic and natural impacts, such as land use
restriction and zoning.
Introduction
Estuaries are transitional zones where marine and riverine
environments meet, i.e., where freshwater from a river
mixes with saltwater from the sea. Here, many habitats,
species, and ecological communities exist, and their ecosystem and naturalistic values are widely recognized.
Along coasts, river banks, and nearshore profiles are
governed by sediment transport equilibrium (i.e., erosion
and deposition phenomena). Alteration of this equilibrium
may result in shoreward recession, leading to land loss.
Since estuarine areas are often used for tourism and recreational purposes, this leads to financial loss as well as ecological community and biodiversity impairment. State and
local authorities thus aim to protect estuarine areas and to
mitigate erosion. A review of the causes of coastal erosion
and an evaluation of the erosion processes are provided
below, together with an analysis of erosion control
measures.
Causes of coastal erosion
There are many causes of coastal erosion processes attributable to natural and anthropogenic factors.
A classification can be based on the temporal scale of such
factors, distinguishing between short- and long-term
events. Natural processes consist of short-term events that
are generally the result of storms and river floods (i.e.,
high-energy content events), while long-term events relate
to sea-level rise (Pranzini and Rossi, 1995; Khalil, 1997),
tidal cycles, tectonic events, coastal subsidence (Khalil,
1997), climate change, river regimes, and discharge flux
(Medina and Lopez, 1997).
In regard to anthropogenic factors, sediment loss is generally due to medium- and long-term events, such as
decreasing sediment supply to coastal physiographic units
(Simeoni et al., 1997; Eronat, 1999; Loizidou and
Iacovou, 1999), deforestation in coastal and riverine
watersheds (Eronat, 1999), non-sustainable man-made
coastal structures and urban development (Fathallah and
Gueddari, 2001; Rakha and Abul-Azm, 2001), flow
regime and engineering structure changes, and riverbed
sand and gravel extraction (PAP/RAC, 2000).
Erosion processes
Suspension and bed load transport can be distinguished
(Fredsøe and Deigard, 1994), the latter mainly causing
the loss of grain size material on the seabed and affecting
long-term and short-term shoreline evolution. Such phenomena are primarily modeled by physical and mathematical and generally consider hydrodynamic and
morphological factors. Hydrodynamic models are based
on the classical equations of motion, with vertical averaged velocities (two-dimension models), and wave propagation, refraction, diffraction, and breaking. They evaluate
velocity flow fields under generic forcing (Figure 1).
Morphological models consider seabed characteristics
and evaluate bed load and shoreline evolution, for both
long-term and short-term conditions (Figure 2).
Physical models are based on two-dimensional and
three-dimensional laboratory scale similarity models that
use channels or large basins (Figure 3) to study both bed
load processes and evaluate the effectiveness of the structural design.
Finally, it should be pointed out that both physical and
mathematical models require a detailed knowledge of seabed morphology, waves and currents (i.e., river or tidal
currents or wave-generated currents), bathymetric surveys, and sediment characterization (pebble or sand
beaches, sediment grain size, and erodibilty changes).
Coastal erosion risk mitigation
A coastal erosion control project should be developed
with reference to coastal cells (Eurosion, 2004), which
are lengths of coastlines in which a complete sediment balance can be identified. Spatial and temporal erosion phenomena scales should also be identified. Acute and
structural erosion can be distinguished. Acute erosion is
connected to waves, wind, and tidal action and typically
covers temporal and spatial scales up to 1 month and from
about 1 m to 100 km, respectively. On the contrary, structural erosion involves larger temporal and spatial scales,
from about 1 month to 100 years and from 1 to
1,000 km, respectively (Safecoast, 2008).
Depending on spatial scale, coastal erosion control
measures can target (1) specific river bank sections and
COASTAL EROSION CONTROL
131