EM 1110-2-1100 (Part V)
31 Jul 2003
moved offshore can be swept into tidal channels, carried away by currents into the inlet's shoals, and not
return to the beach face. This will result in a significant permanent loss of sand. Different design concepts
may be utilized in each of these two cases. In the former case, beach fill alone may meet the design
requirements. In the latter, structures such as T-groins, may be needed to improve beach-fill retention.
Different design methods may be utilized in each case. The former case may lend itself to simple analytical
design tools, whereas the latter case may require more sophisticated physical or numerical modeling to aid
in the design.
(2) Pathways of sediment movement.
(a) Because beach nourishment projects involve placing additional sand into the littoral system, project
design is greatly aided by knowing how sand presently moves within the project domain and the littoral cell
that is the setting for the project. Specifically, the following pieces of information are valuable: knowledge
of the quantities of sand that presently enter and leave the littoral cell, where the sand enters and leaves, and
what quantity moves through the project site. The more information known about the movement of sand the
better, although this "picture" can be difficult to develop, especially for project sites with sparse data.
Estimates of these quantities are often developed through formulation of a sand budget for the littoral cell and
project domain. Parts IV and VI discuss development of a sediment budget. The following are types of
questions regarding pathways and quantities of sand movement that might be important to the design of the
project. If a project is to be constructed within a littoral cell flanked by inlets, are the inlets bypassing sand
into the cell? If so, how much is bypassed? Are structures present that might be blocking (partially or
completely) the flux of sand into the site from adjacent beaches? Is the project site located on a convex
stretch of the barrier island that may be undergoing persistent erosion, or is the site in an area that experiences
intermittent periods of erosion and accretion? Is the project to be located in a pocket beach flanked by
headlands, and are those headlands blocking longshore sand transport? Are there sources of sand within the
littoral cell, such as a river or lagoon, that might periodically discharge sediments to the beach system, or
bluffs behind the beach that might serve as a sediment source? Are there sinks within the littoral cell, such
as offshore canyons, impoundment fillets updrift of coastal structures, or loss of sand into an adjacent inlet
and its shoal system? The closer to inlets, the greater the chance that tidal currents will have an important
role in defining sediment pathways. It is important to gain an understanding of the littoral processes at work
in the region, including the magnitude and direction of longshore sand transport (net and gross transport
rates), sand sources and sinks, and the effects of existing coastal structures on the movement of sand. Parts
III-2 and III-3 address the subject of longshore and cross-shore sediment transport processes, respectively,
in greater detail.
(b) Historical and current charts, maps, and aerial photographs provide valuable information about the
regional setting for a project. They can be valuable data sets for characterizing littoral processes at a project
site, and aid in developing a sand budget. A persistent signature of impoundment at coastal structures over
several years provides evidence of predominant wave direction and net longshore sand transport direction.
Formation and evolution of spits, or migration paths of submerged relic ebb tidal shoals, can provide the same
information. Noticeable changes in shoreline orientation and curvature, or persistent changes in bathymetric
contour orientation may indicate gradients in longshore sand transport rates or a change in net transport
direction. Shoreline positions that are accurately digitized from properly rectified aerial photos and/or charts
provide information for identifying current and past erosional and accretional areas, and for calculating
shoreline change rates. Calculated change rates can be used to estimate changes in sand volumes along
different portions of the beach. Nautical charts and bathymetric surveys show the presence of canyons and
proximity of the canyons to the shore, tidal channels, shoals, other morphologic features, and changes in these
features through time. Controlled bathymetric surveys (relative to common horizontal and vertical datums)
can be analyzed to determine volume changes for use in formulating a sand budget.
Beach Fill Design