EM 1110-2-1100 (Part V)
31 Jul 2003
increases naturally. If the berm is constructed to an elevation that is much higher than the natural berm crest,
an undesirable persistent scarp may form along the shoreline.
(c) For practical and economic reasons, during the construction of the beach berm, the total fill volume
required to advance the berm to the desired width is placed on the visible portion of the beach. This
construction method, sometimes referred to as the "over-building" method, enables the economic use of
standard earth-moving equipment for the distribution of the fill and minimizes relocation of the discharge
point. The method also enables effective verification that the sectional fill volume (design fill volume per
unit length of shoreline) has been placed on the beach by the contractor using standard land-based survey
techniques. The result of this construction technique is a beach berm that is initially considerably wider than
the target design width. Postconstruction berm widths are often two to three times wider than the target
design width. Design specifications required a 30-m (100-ft) design berm width in the northern New Jersey
beach nourishment project while postconstruction surveys indicated constructed berm widths of 60 to 90 m
(200 to 300 ft) and along some survey lines berm widths approaching 120 m (400 ft) were measured. While
recognized by project designers, lay persons are often unaware that the initial overbuilt berm is a temporary
condition. Consequently, they incorrectly judge the project as a failure when the beach berm adjusts
dramatically landward immediately after construction, especially during the first storm season. For this
reason, it is important that public outreach programs include easy-to-understand information concerning the
expected remolding of the fill material after initial construction. Figure V-4-2 provides a schematic
illustration of the preproject beach profile, the post-construction over-built beach berm, and the expected
design berm after cross-shore equilibration.
(2) Dune.
(a) Sand dunes are an important protective feature. Naturally occurring dune ridges along the coast
prevent storm tides, wave runup, and overtopping from directly damaging oceanfront structures and flooding
interior areas. Dune features of beach nourishment projects are intended to function in the same way. A
beach nourishment project may involve either reinforcing an existing natural dune by adding elevation and/or
cross-sectional area, or constructing a dune where none existed beforehand. Dunes also provide a small
reservoir of sand for nourishing the beach during severe storms. However, after the storm, maintenance is
required to rebuild the dune because natural dune rebuilding occurs at a much slower rate than natural berm
rebuilding.
(b) During hurricanes and very severe northeasters, substantial sections of dune can disappear. This is
caused by offshore transport of dune material into the surf zone and by beach and dune sediments being swept
landward by wave uprush and overtopping. In the case of overtopped barrier islands, flooding from ocean-
side storm surges and waves and/or return flow of water from flooded bays can erode enough sand to cut
shallow channels, or breaches, through the island. Occasionally, the channels will evolve into new inlets.
Areas most prone to breaching are those where the barrier island is narrow and the dunes are lowest or
nonexistent. The crest elevations of natural dunes often varies considerably, and nature tends to erode the
low spots first. Dunes and berms built as part of a nourishment project can reduce the potential for barrier
island breaching because a relatively uniform dune elevation eliminates the low spots where breaches are
most likely to form.
(c) Dune growth can be promoted and the dune structure can be made more resistant to erosion if suitable
vegetation can be grown on the dunes for an adequate length of time to establish an extensive root system.
It generally takes 2 to 5 years for beach grass to establish a healthy root system, and up to 10 years before
the maximum resistance to erosion and breaching is obtained. An active grass fertilization and
Beach Fill Design
V-4-3
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