EM 1110-2-1100 (Part V)
31 Jul 2003
frequency-of-occurrence relationships, whereby return periods are associated with storm responses
rather than storm input. Scheffner and Borgman (1999) provide detailed guidance in applying the
EST to coastal studies. Advantages of this approach are that it involves no arbitrary assignment of
recurrence relationships and it utilizes historical rather than representative or hypothetical events to
determine frequency-of-occurrence relationships. Part II discusses methods for estimated storm
waves and water levels.
Because water level is a primary factor controlling beach erosion, tide variations should be
considered when developing the input storm set. Tide variations can be accounted for by combining
storm surges with different tidal phases and ranges. For example, peak storm surges may be aligned
with high tide, low tide, midtide preceding high tide, and midtide preceding low tide to generate four
different but equally probable events derived from each base storm. Variations in tide ranges (neap,
spring, and average) may also be considered in developing a full set of storms.
(c) Storm erosion modeling.
Upon selection of design alternatives, characterization of the without-project condition, and selection
of the storm set, storm-induced beach erosion modeling is performed to calculate parameters required
for assessing economic damages based on beach erosion, flooding, and wave attack. The SBEACH
model computes relevant storm response parameters such as recession distance, maximum water level
and wave height at the shoreline, and wave runup. Required input to the model includes beach
profiles describing the design alternatives and without-project condition, time-histories of storm
water level, wave height and wave period, median sand grain size, and calibration parameters.
Detailed examples and guidance for applying the SBEACH model to predict storm erosion are
provided in the SBEACH technical report series (Larson and Kraus 1989; Larson, Kraus, and Byrnes
1990; Rosati et al. 1993; Wise, Smith, and Larson 1996; and Larson and Kraus 1998).
(d) Storm damage recurrence relationships and risk analysis. Modeled erosion responses are expressed
in terms of frequency of occurrence for input to economic damage models. Typically, tropical and extra-
tropical erosion responses are joined to generate a combined frequency curve spanning the recurrence
intervals of interest. Risk and uncertainty of storm damage parameters can be addressed by developing mean-
value frequency-of-occurrence curves together with confidence bands that indicate the variability or
uncertainty associated with the calculated storm responses.
The EST and supporting analysis tools can be used to calculate mean-value frequency curves and
confidence bands. Figure V-4-18 shows an example of frequency-of-occurence relationships
generated by the EST technique. The solid line represents the mean or expected value of beach
recession as a function of return period, and the dashed lines show the 90 percent confidence band,
indicating that 90 percent of variability in beach recession for a given return period falls within these
limits.
(6) Cross-sectional fill volume requirements.
(a) A key quantity in beach-fill design is the volume of sand required to produce the desired
beach cross-section. The design profile is determined using methods presented in Part V-4-1-f-(4) and
results from the optimization process outlined in Part V-4-1-f-(5). The berm width is then increased to
reflect the amount of advance nourishment needed to maintain the design profile prior to the first
renourishment. The modified design profile shape, which includes advance nourishment, is then estimated
V-4-38
Beach Fill Design
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