EM 1110-2-1100 (Part V)
31 Jul 2003
placed shallower than the depth of closure (see Part III-3-3-b), it is expected that with time, the material will
move onshore, eventually becoming part of the beach berm and beach face system. The material placed in
the nearshore berm, however, does not provide direct shore protection to the upland, and prototype experience
with the practice has met with mixed results and uncertain net benefit.
(4) Feeder beach. Beach-fill projects usually involve placement of a berm along a finite length of
shoreline. Sometimes, beach nourishment projects include the creation of a feeder beach, in which fill
material is introduced at the updrift end of the area intended to receive the fill. Then, longshore transport
distributes the fill to the rest of the project area. Feeder beaches work best in areas that serve as a source of
littoral material for downdrift beaches, in areas that are presently experiencing a deficit in the supply of
littoral material and have unusually high loss rates, and in areas where the net longshore transport direction
is predictable and the net transport rate is "strong" (i.e., longshore sand transport in one direction greatly
exceeds the transport in the other direction). Candidate sites for feeder beaches include areas immediately
downdrift from inlets or other manmade structures that form a littoral barrier or in areas that have been
identified as erosional "hot spots." As the feeder material spreads under the influence of waves, the
orientation of the feeder beach shoreline approaches that of the adjacent beach, resulting in longshore
transport out of the feeder area equal to the transport along the adjacent area. Eventually, the shoreline
orientation in the feeder beach area will return to its original configuration. Protection provided by feeder
beaches will not have the same degree of alongshore uniformity as that provided by placing fill in a
prescribed manner throughout the project area.
(5) Structures in conjunction with beach nourishment. Structures can enhance the performance of a
beach nourishment project. Figure V-4-3 shows several such examples. When the project is relatively short
in length, or significantly affected by an inlet, it may be desirable to limit alongshore losses through the use
of a terminal structure or structures (Figures V-4-3a and V-4-3b show examples). Another use of structures
is to place them in the interior of the nourishment project, with the intent of increasing project longevity
(Figure V-4-3c) by reducing the longshore sand transport rate and minimizing end losses. Structures can also
be used locally within a project to maintain the desired level of protection. For example, structures may be
used to compartmentalize and stabilize a beach in anticipation of, or in response to, an area of unusually high
volume losses (i.e., presence of a hotspot). Whenever structures are used, their potential updrift and
downdrift impacts should be assessed. It is important to note that structures do not create sand, they only
control its movement. If structures are built without adding beach fill, then sand may accumulate at one
location at the expense of erosion at another area. As a general rule, compartments between structures, and
the beach immediately updrift and/or downdrift of the structures, should be filled with sand to minimize
adverse effects on adjacent beaches. Potential adverse effects of a groin field can be minimized by tapering
the lengths of groins at the end of the groin field (see Figure V-4-3c), and adding sand on the downdrift side
of the project. Part V-4-1-i provides additional information about the functional design of structures used in
conjunction with beach fill projects. Part VI presents information on the structural design aspects of coastal
structures.
c. Define regional setting and site history. To maximize a beach nourishment project's effectiveness,
it is important to understand the project's physical setting. The term "setting" encompasses local- and
regional-scale coastal processes, the geology, and infrastructure that characterize the site and surrounding
area. Part V-3 provides a general discussion of site characterization for all coastal projects. The following
sections focus on those aspects that are most pertinent to engineering design of beach nourishment projects.
A beach fill project can be a significant perturbation to the coastal system, and project performance is directly
related to its interaction with its surroundings. The following are a few questions regarding project setting
that should be answered at the beginning of the design process: In what type of littoral system, or littoral cell,
will the project be constructed?
Beach Fill Design
V-4-5
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