EM 1110-2-1100 (Part V)
31 Jul 2003
The overfill method previously described is the Krumbein-James technique (Krumbein and James
1965). Dean (1974) presents an alternative method for computing the overfill factor, not shown,
which generally yields less conservative (lower) estimates of the overfill factor.
f. Beach-fill cross-section design. The design of Federal beach-fill projects is based on the optimization
of net annual benefits defined as the difference between average annual costs and average annual benefits.
This optimization procedure produces a plan known as the National Economic Development (NED) plan.
The NED plan considers the storm damage reduction potential of various beach fill design alternatives and
the averaged annual cost. Primary design parameters of each alternative include the physical dimensions of
the cross-sectional design profile and the volume of sand required to obtain the design profile. Beach-fill
design alternatives typically include combinations of beach berms of varying width and dunes of varying
height (see Part V-4-1-b for a description of the characteristics and functions of beach berms and dunes).
Design berms are characterized by berm crest elevation and berm width. Dune design dimensions include
crest elevation, crest width, and side slopes.
(1) Berm elevation. The elevation of the design berm should generally correspond to the natural berm
crest elevation. If the design berm is lower than the natural one, a ridge will form along the crest, which,
when overtopped by high water will produce flooding and ponding on the berm. A design berm higher than
the natural berm will produce a beach face slope steeper than the natural beach and may result in formation
of scarps that interfere with sea turtle nesting and recreational beach use. Many healthy, natural beaches
exhibit a gentle downward slope from the toe of the dune to the seaward limit of the berm. Therefore, a
gentle berm slope can be specified as an element of the design profile. The berm slope is most appropriately
estimated from profiles that represent a nearby, healthy beach. Or the slope can be estimated to fall in the
range from 1:100 to 1:150. Adding a gentle slope to the berm also helps prevent overtopping and ponding.
(a) The natural berm elevation can be determined by examining beach profile surveys of existing and
historical conditions at the project site. Because beach berms form naturally under low-energy waves, they
are typically most well-developed in form at the end of the summer season. Seasonal profile surveys can be
used to examine temporal changes in berm shape and to identify well developed berm features from which
to estimate the natural berm height. When survey data indicate alongshore variations in the natural berm
height, a representative berm height may be determined either by visual inspection of plots showing the
alongshore variations or by computing an average profile shape. The Beach Morphology Analysis Package
(BMAP) provides automated calculation and visualization tools for performing such analyses. Sommerfeld
et al. (1994) provide an overview of the capabilities and a user's guide for operation of the BMAP software.
(b) Figure V-4-10 shows an example of seasonal variation in berm shape measured over two consecutive
years at a given profile station. The fall surveys show that the beach berm is widest following the calmer
summer waves, whereas the spring surveys show the berm to be in a more eroded condition following winter
waves. Based on visual inspection of Figure V-4-10, a natural berm height for this profile can be
approximated by the horizontal dotted line, corresponding to an elevation of 3.6 m. Figure V-4-10 shows that
it would be difficult to identify the natural berm height based solely on the first spring survey, and illustrates
the advantage of using multiple surveys for profile characterization.
(c) Figure V-4-11a shows beach profiles measured during a single fall survey at five different profile
stations along the beach. The berm is seen to vary alongshore in height and width. To determine a
representative berm height, the beach profiles are horizontally aligned on the seaward face of the dune to
superimpose the berm profiles at the base of the dune, as shown in Figure V-4-11b. An average profile is
computed by averaging the elevations of the aligned profiles at 1-m increments in distance offshore.
Figure V-4-11c shows the average profile, from which a representative berm elevation of 3.5 m is obtained
by inspecting the horizontal portion of the profile between the offshore distances of 75 and 100 m.
Beach Fill Design