EM 1110-2-1100 (Part V)
31 Jul 2003
cross sections and varying berm widths. The SBEACH model was used to simulate profile change, and each
profile was subjected to a constant wave height of 3 m, wave period of 10 sec, and water level of 1.5 m msl
over a duration of 24 hr. Figure V-4-12b shows the calculated results for each profile. The profile with no
berm experienced complete erosion and overtopping of the dune. Most of the dune was eroded on the 10-m
berm profile, whereas the 25-m berm profile experienced only minor dune erosion. The 40-m berm provided
full protection against erosion of the dune and backbeach, and some sand was pushed up against the base of
the dune due to overwash across the wide berm. In this example, a shorefront property located immediately
landward of the dune would experience varying degrees of damage and/or vulnerability to future storm
erosion and flooding as a function of the beach berm width.
(b) Factors other than storm erosion that influence beach width include the rate and variability of long-
term shoreline recession, planform spreading losses, and presence of erosional hot spots. These factors
typically do not enter in the optimization of the design berm width for storm damage reduction projects, but
should be accounted for in optimization of the advanced fill section and renourishment interval as discussed
in Part V-4-1-g.
(c) Storm berms may be used in conjunction with a natural berm to provide added protection against
damage during storms. Storm berms are constructed at an elevation higher than the natural berm and are set
back, landward, from the crest of the natural berm. Storm berms are built to reduce the chance for wave
action and erosion from reaching the dune during higher water levels associated with a specified degree of
storm intensity (usually, the type of storm that can be expected once every few years). The crest elevation
of a storm berm should be set based on the water level and runup elevation associated with the type of
storm(s) against which protection is sought. If a storm berm is included in the design, the width of the storm
berm can be optimized to maximize net benefits. The seaward extent of the storm berm should also consider
the possibility for undesirable, persistent scarp formation.
(3) Dune dimensions.
(a) Dunes protect upland property against wave attack, erosion, and flooding during extreme storm
events which overtop or severely erode the beach berm. Design parameters of a dune include the crest
elevation, crest width, and side slopes. The design dune crest elevation is typically determined through
economic optimization. The dune crest width may also be optimized but is typically fixed at a selected width
for all design alternatives. In selecting dune crest width and side slopes, constructibility constraints and angle
of repose of the fill material grain size should be considered. A typical dune design may have dimensions
on the order of 5-m crest elevation above msl, 10-m dune crest width and one on five side slopes. Planting
beach grasses on the constructed dune helps to maintain and build dune volume over time by trapping wind-
(b) To illustrate the influence of dune height on storm-induced beach profile change, the no-berm profile
shown in Figure V-4-12 was modified to increase the dune elevation from 4 to 4.5 m while maintaining the
same crest width and side slopes. The original and modified dune configuration are shown in Figure V-4-13a.
The increase in dune height translates to an added volume of 10 cu m/m for this profile. Figure V-4-13b
shows profile erosion modeled by SBEACH for the same storm conditions used in the previous berm erosion
example. The calculated results in Figure V-4-13b indicate the added dune height prevented dune
overtopping and back-beach erosion for these particular wave and water level conditions.
(4) Design profile shape. The shape of the design profile is needed to compute cross-sectional fill
volume requirements and as input to storm-induced erosion modeling that is done to optimize berm and dune
dimensions. In order to obtain the design dune and berm template on the beach, sufficient sand must be
placed to nourish the entire profile out to the depth of closure (see Figure V-4-14 and Part III-3-3-b for details
Beach Fill Design