EM 1110-2-1100 (Part V)
31 Jul 2003
or on the open coast, project reaches should be of sufficient length to minimize the effect of end losses on the
central portion of the project. Part V-4-1-g discusses design parameters and environmental processes that
affect project longevity. Economic analyses may identify several discontinuous subreaches within the project
main reach (e.g., where areas of development are separated by areas of undeveloped coast). In such cases,
a project may function more effectively by designing a single reach spanning both developed and
undeveloped sections to avoid multiple areas of end losses.
(3) Beach-fill projects have often employed a uniform design template, with constant berm width and
dune elevation, along the entire project. Under most circumstances, however, improved performance can be
achieved by modifying the design template along specific subreaches where longshore nonuniformity exists
in the without-project condition. For example, consider an existing condition where a particular
shore-fronting structure is positioned closer to the shoreline than adjacent structures. A design calling for a
uniform width of beach in front of all structures along the entire project reach will produce a planform
perturbation at the protruding structure, and will lead to an ongoing problem of accelerated recession in front
of the structure. In this case, a viable alternative may be to design a narrower berm in the area of the
protrusion with additional storm damage protection provided by higher dunes or protective structures such
as seawalls. Other cases where nonuniform design templates may be appropriate include presence of
erosional hot spots, changes in shoreline orientation, or nonuniform placement of shore protection structures
along the project reach. In design, a practical goal is to distribute the sand fill volume alongshore so as to
yield a more or less uniform shoreline location after initial equilibration of the placed fill. Care must be taken
in using a variable design template to avoid compromising project performance. For example, dunes placed
in front of a developed subreach to prevent overtopping and flooding may not be functional if lower dunes
or no dunes are placed on adjacent subreaches of undeveloped shore. In this case, storms could erode and
overtop the adjacent low dunes and flank the high dunes, resulting in flooding of the developed area.
e. Evaluate sediment sources.
(1) Borrow source types. Borrow sources for beach fill can be divided into four general categories:
terrestrial, backbarrier, offshore, and navigation channels. Each category has favorable and unfavorable
aspects; however, selection of an optimum borrow source depends more on individual site characteristics
relative to project requirements than type of source. The single most important borrow material characteristic
is the sediment grain size.
(a) Terrestrial sources. Terrestrial sources of beach-fill material can be found in many coastal areas.
Ancient fluvial and marine terrace and channel deposits, and certain glacial features such as eskers and
outwash plains often contain usable material. Because of their potential economic value, information on sand
and gravel deposits is often collected by state geological surveys. With this information, field investigations
can focus on a few likely sources, thus eliminating need for more general exploration. In some places,
commercial sand and gravel mining operations may provide suitable material for direct purchase. In their
absence, it would be necessary to locate a suitable deposit and set up a borrow operation specifically for the
project. Use of terrestrial borrow sites usually involves lower costs for mobilization-demobilization
operations and plant rental, and less weather-related downtime than the use of a submerged borrow source.
However, the production capacity of terrestrial borrow operations is comparatively low, and haul distances
may be long. Thus, costs per unit volume of placed material may exceed those from alternate submerged
sites. In general, terrestrial borrow sources are most advantageous for projects where exploration and
mobilization-demobilization costs, relative to the cost of fill, are a large part of overall expense of the
operation. Unfavorable aspects of terrestrial borrow sources are typically related to adverse secondary
impacts caused by mining and overland transport. Compared to hydraulic placement, mechanical (dump
truck) placement of fill additionally results in practical limits in fill volume, and fill placement is mostly
limited to the dry and intertidal beach. Consequently, more rapid equilibration and recession of the placed
fill is experienced.
Beach Fill Design