Beach Nourishment 29.5 Additional Design Considerations 643
Part C | 29.5
change data are available is to determine the wave direction corresponding to the best fit of the solution to
the measured data. Figure 29.9 presents the best fit of
the P-C methodology to the data presented earlier in
Fig. 29.6. In this case, the associated value of the longshore diffusivity G, and angle  ˛ are 0:0111 m
2
=s
and 8:65
ı , respectively.
Figure 29.10 presents results from a laboratory experiment in which measurements on the updrift side of
a groin compare favorably with the P-C theory.
29.4.2 One-Line Numerical Models
One-line numerical models have a considerable advantage over the P-C method in terms of the flexibility they
offer allowing groins or other coastal features such as
inlets with or without bypassing to be introduced into
the design. Many such models have been developed,
some to an advanced level of detail. The US Army
Corps of Engineers has developed the GENESIS model
to a level that allows application to a variety of useful
design conditions including groins and detached breakwaters [29.7, 10, 11].
29.4.3 N-Line and more Detailed Models
More complex models allow the third (vertical) dimension to be represented and thus, in principle, provide
much more valuable information than the less complex
models. Some of these models are in the research rather
than the application arena. Application of all models requires some calibration with the more complex models
usually requiring the greatest amount of calibration to
achieve the level of detail desired.
Delft3D is a comprehensive, publicly available,
process-based modeling suite that simulates twodimensional (2-D) and three-dimensional (3-D) flows,
sediment transport and morphology, waves, water quality and ecology and is capable of representing the interactions between these processes. The suite is designed
for use by experts and nonexperts, which may range
from consultants and engineers or contractors, to regulators and government officials, all of whom are active
in one or more of the stages of the design, implementation, and management process. Delft3D is suitable
for simulating erosion and deposition over storm-length
(714 day) or project-length (510 year) time scales
and handles a variety of coastal structures. Morphology type models like Delft3D offer distinct advantages
over N-Line models because they are capable of updating three-dimensional bathymetric features at each
time-step, thus providing feedback to the wave and flow
models for a more complete simulation of the coastal
environment. Delft3D requires an extensive amount of
data and time to set up and run, and therefore may not
be the best option for many applications.
29.5 Additional Design Considerations
29.5.1 Erosional Hot Spots
In beach nourishment projects, erosional hot spots
(EHSs) are defined as areas that erode more rapidly
than the adjacent areas or possibly areas that erode
more rapidly than anticipated in the design. EHSs occur in nearly all beach nourishment projects and may or
may not be predictable. In a celebrated case at Grand
Isle, LA, USA [29.12], the nourished beach advanced
significantly landward of the two seaward borrow areas. These borrow areas which may reported to have
filled with very fine sediment and caused significant
damping of the waves (personal communication, A. J.
Combe). These borrow pits acted as detached breakwaters in reducing the shoreward wave heights causing
shoreline advancement landward of the dredge pits and
erosional hot spots adjacent to these advancement areas. Benedet and List [29.13] applying Delft3D, have
correlated EHSs on the Delray Beach, FL, nourishment
project with the seaward borrow areas.
The EHSs experienced at Grand Isle, LA, are exceptional; however, EHSs that occur in typical nourishment projects are not inconsequential. Figures 29.11
and 29.12 present the performance of the 1992 Anna
Maria Key, FL, beach nourishment project. This project
was 6:7 km in length with a nourishment volume of
1:78 million m
3 . The initial additional beach width varied from 55 to 107 m and the nourishment volume
density varied from 200 to 350 m
3
=m. The most recent survey (February 1999) in these figures is for 6
years after nourishment and as of that time, the change
in immediate postnourishment volumes ranged between
a loss of 320 to a gain of 160 m
3
=m. The corresponding
shoreline width reductions ranged from 37 to 69 m. The
borrow area for this project was located between monuments 2534 and was fairly close to shore. Thus, some
of the postnourishment changes in these figures could
be due to the proximity of the borrow pit; however,
some changes for other areas within this project are
significant and generally cannot be predicted by any numerical models. The shoreline recession includes both
volume loss and profile adjustment toward equilibrium.
Shoreline irregularities also exist along natural
beaches. Often this occurs during mild wave conditions
Part C | 29.5
change data are available is to determine the wave direction corresponding to the best fit of the solution to
the measured data. Figure 29.9 presents the best fit of
the P-C methodology to the data presented earlier in
Fig. 29.6. In this case, the associated value of the longshore diffusivity G, and angle  ˛ are 0:0111 m
2
=s
and 8:65
ı , respectively.
Figure 29.10 presents results from a laboratory experiment in which measurements on the updrift side of
a groin compare favorably with the P-C theory.
29.4.2 One-Line Numerical Models
One-line numerical models have a considerable advantage over the P-C method in terms of the flexibility they
offer allowing groins or other coastal features such as
inlets with or without bypassing to be introduced into
the design. Many such models have been developed,
some to an advanced level of detail. The US Army
Corps of Engineers has developed the GENESIS model
to a level that allows application to a variety of useful
design conditions including groins and detached breakwaters [29.7, 10, 11].
29.4.3 N-Line and more Detailed Models
More complex models allow the third (vertical) dimension to be represented and thus, in principle, provide
much more valuable information than the less complex
models. Some of these models are in the research rather
than the application arena. Application of all models requires some calibration with the more complex models
usually requiring the greatest amount of calibration to
achieve the level of detail desired.
Delft3D is a comprehensive, publicly available,
process-based modeling suite that simulates twodimensional (2-D) and three-dimensional (3-D) flows,
sediment transport and morphology, waves, water quality and ecology and is capable of representing the interactions between these processes. The suite is designed
for use by experts and nonexperts, which may range
from consultants and engineers or contractors, to regulators and government officials, all of whom are active
in one or more of the stages of the design, implementation, and management process. Delft3D is suitable
for simulating erosion and deposition over storm-length
(714 day) or project-length (510 year) time scales
and handles a variety of coastal structures. Morphology type models like Delft3D offer distinct advantages
over N-Line models because they are capable of updating three-dimensional bathymetric features at each
time-step, thus providing feedback to the wave and flow
models for a more complete simulation of the coastal
environment. Delft3D requires an extensive amount of
data and time to set up and run, and therefore may not
be the best option for many applications.
29.5 Additional Design Considerations
29.5.1 Erosional Hot Spots
In beach nourishment projects, erosional hot spots
(EHSs) are defined as areas that erode more rapidly
than the adjacent areas or possibly areas that erode
more rapidly than anticipated in the design. EHSs occur in nearly all beach nourishment projects and may or
may not be predictable. In a celebrated case at Grand
Isle, LA, USA [29.12], the nourished beach advanced
significantly landward of the two seaward borrow areas. These borrow areas which may reported to have
filled with very fine sediment and caused significant
damping of the waves (personal communication, A. J.
Combe). These borrow pits acted as detached breakwaters in reducing the shoreward wave heights causing
shoreline advancement landward of the dredge pits and
erosional hot spots adjacent to these advancement areas. Benedet and List [29.13] applying Delft3D, have
correlated EHSs on the Delray Beach, FL, nourishment
project with the seaward borrow areas.
The EHSs experienced at Grand Isle, LA, are exceptional; however, EHSs that occur in typical nourishment projects are not inconsequential. Figures 29.11
and 29.12 present the performance of the 1992 Anna
Maria Key, FL, beach nourishment project. This project
was 6:7 km in length with a nourishment volume of
1:78 million m
3 . The initial additional beach width varied from 55 to 107 m and the nourishment volume
density varied from 200 to 350 m
3
=m. The most recent survey (February 1999) in these figures is for 6
years after nourishment and as of that time, the change
in immediate postnourishment volumes ranged between
a loss of 320 to a gain of 160 m
3
=m. The corresponding
shoreline width reductions ranged from 37 to 69 m. The
borrow area for this project was located between monuments 2534 and was fairly close to shore. Thus, some
of the postnourishment changes in these figures could
be due to the proximity of the borrow pit; however,
some changes for other areas within this project are
significant and generally cannot be predicted by any numerical models. The shoreline recession includes both
volume loss and profile adjustment toward equilibrium.
Shoreline irregularities also exist along natural
beaches. Often this occurs during mild wave conditions