EM 1110-2-1100 (Part V)
31 Jul 2003
transitions sections have rarely been constructed to this length. In practice, the exact length of the fill
transition section does not ultimately matter so long as it is in reasonable proportion to the scale of the project.
Typical fill transition lengths for small projects (approximately 1 to 2 km; 100,000 to 200,000 m3) are on the
order of 150 to 300 m (500 to 1000 ft) long, while for larger projects they are on the order of 300 to 600 m
(1000 to 1,500 ft) long.
(11) Transition sections do reduce the rate of fill loss from the project; but again, this benefit lasts only
for the first few years following construction. Some past project designs have inappropriately estimated the
beneficial effects of the beach-fill transitions by computing the reduction in the rate of end loss during the
first few years of the project and then projecting these benefits throughout the 50-year project life. The
analysis presented here suggests that while benefits associated with reduced loss rates are very high during
the first few years, they diminish significantly thereafter.
(12) An analysis of beach-fill transitions should first examine the evolution of the project with transition
sections, either tapered sections or lateral extensions of the design section, and then examine evolution of the
project with the transition volume distributed within the project economic benefit area. The distribution
within the project doesn't have to be uniform, as was the case in the examples shown here. If transitions are
a desirable feature, they should be optimized by balancing the reduction in the rate of end losses from the
project (which will reduce renourishment costs) with the cost of placing fill volume outside of the project's
economic benefit area. Then, costs of the transition sections over the project life should be compared to the
cost of using a terminal structure or compartmentalizing the beach-fill material with groins or jetties,
including an assessment of any impacts that might be caused by a terminal structure. The most cost-effective
approach should be selected. Environmental concerns, land ownership constraints, or other factors may also
need to be considered in the selection of the optimum fill transition sections.
i.
Beach-fill stabilization measures.
(1) Structures. Different types of structures can be used in conjunction with beach-fill projects to retard
fill erosion and thereby reduce periodic renourishment costs. As discussed in the previous section, losses are
particularly pronounced at the ends of a project where an offset occurs between the fill section and the
adjacent unfilled beach. Structures may be needed in these transition zones to keep fill losses at acceptable
levels. In some cases, structures may already be in place on the project beach. Depending on type and
location of these structures, it may be advantageous to retain them, and perhaps refurbish them. However,
some structures may have a negative effect on the beach, or are undesirable from the standpoint of aesthetics
or safety. If existing structures are judged to have a probable negative effect, their removal should be
considered. Following is a brief discussion of coastal structures in common use in conjunction with beach-fill
projects. A more detailed discussion of their characteristics, effects, and design can be found in Part VI.
(a) Groins.
Groins are low linear structures which are typically built perpendicular to the shoreline, extending
from the beach into shallow nearshore water. Their primary purpose is to trap and retain sand
moving in the alongshore direction. Groins can be constructed in groups, or fields, consisting of
a series of structures spaced at predetermined intervals along a segment of shore to improve
retention of beach-fill material, Figure V-4-29, or as an individual structure intended to provide
effective termination of a beach-fill project. Weggel and Sorensen (1991) note that the addition and
modification of groins within the Atlantic City, New Jersey, nourishment project, constructed in
1986, improved fill performance when compared to that of previous fills for the same location. The
groins acted to retain the fill within the project area and prevented fill losses into the adjacent inlet.
In the context of beach nourishment projects, the most common use of the groin is as a terminal
structure, designed to reduce or eliminate sediment losses out of the project area. The use of a
Beach Fill Design
V-4-71
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