EM 1110-2-1100 (Part V)
31 Jul 2003
monitoring data also can shed light on a design deficiency. Monitoring and analysis of data are discussed in
more detail in Part V-4-1-l.
(2) Advance nourishment. Advanced nourishment is the volume of sand that is placed for "sacrificial"
purposes during initial construction to maintain the design fill section during the initial renourishment interval
(i.e., the time from project completion to the first scheduled renourishment). The magnitude of the advance
nourishment should be determined based on results from work done to assess lateral spreading losses and
volumetric losses due to long-term shoreline recession, i.e., the historic or background erosion rate. The
postproject shoreline erosion rate will be greater than the preproject historic or background erosion rate in
those cases where the preproject beach featured a sediment deficit or was otherwise sediment starved. For
example, project reaches that feature an armored shoreline may historically exhibit little or no erosion, but
can exhibit significant background erosion when replenished with sand fill. Advanced nourishment quantities
are included in the initial total construction volume.
(3) Fill parameters affecting lateral spreading. Both simple and detailed methods are available for
estimating the rate of alongshore spreading, and identifying renourishment requirements (both volume and
interval). Simple methods treat the incident wave climate in a more approximate manner, through use of a
representative wave height and neglecting wave direction. They consider the background erosion rate as an
input parameter, and they assume the erosion rate is uniform over the project domain. Simple methods are
generally most applicable to cases that do not involve coastal structures. On the other hand, detailed methods
treat the effects of coastal structures and wave climate more rigorously. They address the issue of alongshore
variation in wave conditions that produce the background erosion rates, as well as alongshore variations in
erosion rates within the project bounds. Detailed methods treat the directionality of the wave climate.
Dominant wave directions become important for projects constructed in the vicinity of engineered structures,
littoral barriers, or sediment sinks, such as inlets. Detailed methods consider the actual planform layout of
the shoreline and structures, whereas simple methods represent them in an idealized manner. In this section,
analytical solutions to the one-line theory of shoreline evolution are examined to reveal the importance of the
following beach nourishment design parameters on lateral spreading losses: length of the nourishment project,
incident wave climate, and ambient background erosion. The analytical approach is extremely useful in
preliminary design and to gain an understanding of the relative importance of these parameters. Detailed
methods are also presented later, which rely on the use of numerical models to evaluate project longevity.
(a) Effect of fill length.
In this section, the effect of beach-fill length (the alongshore extent of the fill) on project longevity
will be examined. The influence of length is best illustrated by considering the most simple case of
an initially rectangular beach fill constructed on a long straight beach with no background erosion.
This situation was first introduced in Part III-2 of this manual where the linearized equation of
longshore sediment transport was combined with the equation of continuity to develop the one-line
theory of shoreline evolution (see Equations III-2-25 and III-2-26). A number of analytical solutions
to this equation were presented. In this section, Equations III-2-31 and III-2-32 will be examined
further to extract additional information pertinent to beach nourishment design. Upon close
examination of Equation III-2-31 it is seen that the important parameter is
a
(V-4-11)
2 gt
where a is one-half the length of the rectangular project, ε is the "shoreline diffusivity" parameter defined in
Equation III-2-26, and t is time. Here it is seen that if the quantity in Equation V-4-11 is the same for two
Beach Fill Design
V-4-49
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