Part C | 30.2
658 Part C Coastal Design
30.2 Coastal Armoring Structures
30.2.1 Types and Purpose
There are many different types of seawalls and dikes,
bulkheads, and revetments as illustrated in Fig. 30.4.
Their functional purposes are different. The seawall
mitigates damage to what lies behind from flooding and
wave forces; the bulkhead prevents the soil behind from
sliding into the sea; and the revetment protects the bank
from erosion. They all have, however, the following in
common:
1. They are located at the land/water interface.
2. They harden (armor) the shoreline to fix its location,
and
3. They have some configuration and crest elevation
that determines the height of the wave run up and
the amount of wave overtopping for the range of
water levels and wave conditions at their location
on the coast.
30.2.2 Functional Design
The functional design of coastal armoring structures involves calculations of wave run-up, wave overtopping,
wave transmission, and reflection. These technical factors together with economic, environmental, and other
constraints all combine to determine the crest elevation
of the structure. We only consider run-up and overtopping due to space limitations.
Wave Run-Up
The wave run-up, R u is defined as the vertical distance
above the still water level that can be reached by the
waves as illustrated in Fig. 30.5. Common practice is
to consider the irregular wave heights following the
Rayleigh distribution and define a run up level exceeded
by i % of the waves as R ui% . One popular, dimensionless, formulation [30.23] is
R ui%
.H s / toe
D .A C C// r b h ˇ ;
(30.1)
where:
H s D the significant wave height at the toe of the
structure
D the surf similarity parameter
A, C D empirical coefficients from laboratory and
field data depending on the value of i, and
D reduction factors (subscripts) for roughness (r),
fronting berm (b), shallow water depths (h), and
wave approach angle (ˇ).
The key independent variable is the surf similarity
parameter, , and three definitions have been employed
in the literature depending on which irregular wave period, T is specified to define the deep water wavelength
L o and the wave steepness S o D H s =L o . The mean wave
period T m , the spectral peak wave period T p ; and the
spectral wave period T m1:0 all have been employed
by various researchers. And, since the structure slope
and wave steepness trigger different types of breaking
waves (spilling, plunging, collapsing, and surging, see
Battjes [30.23]), the coefficients A and C vary with
for a given structure. Hunt [30.24] was the first to introduce (30.1).
For the design of crest elevations with nonovertopping wave conditions, the 2% value for run-up has long
been the choice. See the EurOtop Manual [30.2] for the
history of this choice for design dating back to 1932 in
the Netherlands.
Impermeable embankments (dikes and levees) with
smooth, rough, and rock cover were studied by de Waal
and van der Meer [30.25]. Using the peak wave period
T p to define op , the run-up at the i D 2% exceedance
level, R u2% depended on the breaker type. For op Ä 2,
A D 1:5 and C D 0. When 2 < < op < 34, A D 0 and
C D 3:0. The coefficient of variation
0
D 0:085. When
the impermeable surface is roughened, r was in the
0:50:6 range. See Table VI-5-3 in the CEM [30.1] for
other reduction factors in (30.1).
Rock-armored slopes with impermeable and permeable cores (rubble-mound breakwaters) were studied in
great detail by van der Meer [30.26]. The permeable
structure resulted in a slightly more complicated form
for the dimensionless, wave run-up formulation
R ui%
.H s / toe
D A C B
C
C D :
(30.2)
And, the mean wave period T m was employed to calculate the surf similarity parameter om for use in
correlating the experimental data. For the impermeable
core, the permeability parameter P D 0:1 and the permeable structure P D 0:5 (see Fig. 30.12 in the next
section for a graphical depiction of P).
At the 2% exceedance level for the impermeable
core case A D 0:96, and B D D D 0, when om Ä 1:5;
and A D 0, B D 1:17, with C D 0:46 and D D 0 when
1:5 < < om Ä 3:1. For the permeable core, these coefficients for A, B, and C are the same except now D D 1:97
for all om 3:1. The CEM [30.1] also presents coefficients for A, B, C, and D for other values of the
exceedance level i for use in (30.2). See Table VI-5-5
in the CEM [30.1].
658 Part C Coastal Design
30.2 Coastal Armoring Structures
30.2.1 Types and Purpose
There are many different types of seawalls and dikes,
bulkheads, and revetments as illustrated in Fig. 30.4.
Their functional purposes are different. The seawall
mitigates damage to what lies behind from flooding and
wave forces; the bulkhead prevents the soil behind from
sliding into the sea; and the revetment protects the bank
from erosion. They all have, however, the following in
common:
1. They are located at the land/water interface.
2. They harden (armor) the shoreline to fix its location,
and
3. They have some configuration and crest elevation
that determines the height of the wave run up and
the amount of wave overtopping for the range of
water levels and wave conditions at their location
on the coast.
30.2.2 Functional Design
The functional design of coastal armoring structures involves calculations of wave run-up, wave overtopping,
wave transmission, and reflection. These technical factors together with economic, environmental, and other
constraints all combine to determine the crest elevation
of the structure. We only consider run-up and overtopping due to space limitations.
Wave Run-Up
The wave run-up, R u is defined as the vertical distance
above the still water level that can be reached by the
waves as illustrated in Fig. 30.5. Common practice is
to consider the irregular wave heights following the
Rayleigh distribution and define a run up level exceeded
by i % of the waves as R ui% . One popular, dimensionless, formulation [30.23] is
R ui%
.H s / toe
D .A C C// r b h ˇ ;
(30.1)
where:
H s D the significant wave height at the toe of the
structure
D the surf similarity parameter
A, C D empirical coefficients from laboratory and
field data depending on the value of i, and
D reduction factors (subscripts) for roughness (r),
fronting berm (b), shallow water depths (h), and
wave approach angle (ˇ).
The key independent variable is the surf similarity
parameter, , and three definitions have been employed
in the literature depending on which irregular wave period, T is specified to define the deep water wavelength
L o and the wave steepness S o D H s =L o . The mean wave
period T m , the spectral peak wave period T p ; and the
spectral wave period T m1:0 all have been employed
by various researchers. And, since the structure slope
and wave steepness trigger different types of breaking
waves (spilling, plunging, collapsing, and surging, see
Battjes [30.23]), the coefficients A and C vary with
for a given structure. Hunt [30.24] was the first to introduce (30.1).
For the design of crest elevations with nonovertopping wave conditions, the 2% value for run-up has long
been the choice. See the EurOtop Manual [30.2] for the
history of this choice for design dating back to 1932 in
the Netherlands.
Impermeable embankments (dikes and levees) with
smooth, rough, and rock cover were studied by de Waal
and van der Meer [30.25]. Using the peak wave period
T p to define op , the run-up at the i D 2% exceedance
level, R u2% depended on the breaker type. For op Ä 2,
A D 1:5 and C D 0. When 2 < < op < 34, A D 0 and
C D 3:0. The coefficient of variation
0
D 0:085. When
the impermeable surface is roughened, r was in the
0:50:6 range. See Table VI-5-3 in the CEM [30.1] for
other reduction factors in (30.1).
Rock-armored slopes with impermeable and permeable cores (rubble-mound breakwaters) were studied in
great detail by van der Meer [30.26]. The permeable
structure resulted in a slightly more complicated form
for the dimensionless, wave run-up formulation
R ui%
.H s / toe
D A C B
C
C D :
(30.2)
And, the mean wave period T m was employed to calculate the surf similarity parameter om for use in
correlating the experimental data. For the impermeable
core, the permeability parameter P D 0:1 and the permeable structure P D 0:5 (see Fig. 30.12 in the next
section for a graphical depiction of P).
At the 2% exceedance level for the impermeable
core case A D 0:96, and B D D D 0, when om Ä 1:5;
and A D 0, B D 1:17, with C D 0:46 and D D 0 when
1:5 < < om Ä 3:1. For the permeable core, these coefficients for A, B, and C are the same except now D D 1:97
for all om 3:1. The CEM [30.1] also presents coefficients for A, B, C, and D for other values of the
exceedance level i for use in (30.2). See Table VI-5-5
in the CEM [30.1].