EM 1110-2-1100 (Part V)
31 Jul 2003
(3) Beach topography.
(a) The shape of the beach, above and below water, sheds light on the coastal processes that are at work
at the project site. Beach shape also is an important factor in determining the quantity of beach nourishment
material needed. The existing beach profile shape seaward of the natural berm crest can be a good indicator
of the expected postnourishment beach shape, provided the sand to be placed has similar grain size
characteristics as the native beach and there are no coastal structures or other features that are controlling the
shape of the beach. One situation where the present profile shape may not be a good indicator of the
postconstruction shape would be a beach that is heavily seawalled or reveted, with little to no dry beach in
front of the structure at high tide. In this instance, the present beach shape might be unnatural (overly steep)
due to the loss of a sand supply at the shoreline (i.e., the beach profile is very much starved of sand).
Proximity to a tidal channel or a coastal structure may also produce an "unnatural" beach profile shape,
compared to the shape that might exist for the same sediment characteristics but located away from the inlet
or coastal structure. Also, if the material to be placed has grain size characteristics that are much different
than the native beach, then the present beach profile shape may not be a good indicator of the shape following
nourishment. Use of sand finer than the native sand will produce a beach with gentler slopes; use of coarser
material will result in a beach with steeper slopes.
(b) Dunes are also an important aspect of project setting. Dune elevation, continuity of the dune "line,"
position of the dunes relative to the shoreline, and volume of sand in the dune above the natural berm crest
elevation are important factors in determining the existing level of protection to property and infrastructure.
Well-established vegetated dunes are usually a sign of a healthy beach system. A scarped dune, evidence
of regular overwash, or no dune at all indicate an area vulnerable to storm damage. Beach profile surveys,
or fully 3-D bathymetric and topographic surveys acquired by lidar systems such as systems such as
SHOALS, can effectively characterize the beach/dune system as well as submerged morphologic features.
Analysis of well-controlled beach profiles (relative to consistent horizontal and vertical datums) can provide
volume change information for use in developing a sand budget, selecting design profiles for the nourishment
project, and estimating the required amount of nourishment material.
(4) Sediment characteristics.
(a) Information about the grain size characteristics of the native beach material can shed light on the
coastal processes at work. Systematic variations in median grain diameter along the beach, or evidence of
natural tracers in the sand, may suggest the direction of net longshore transport. Grain size characteristics
are a critical design parameter. Most often, sand with grain size characteristics similar to those of the native
beach is sought as beach-fill. This is done to maximize compatibility with the existing beach system.
Indirectly, selecting compatible material also maximizes the accuracy of predictions of future project
performance, which is often based on past observations of the native beach response. Occasionally, fills are
designed using material with different size properties because of limitations on sand availability and the cost
to transport it to the project site. Sometimes the choice of a nourishment material with different
characteristics is made to satisfy a particular design objective, such as use of coarser-grained fill material to
improve resistance to erosion.
(b) Grain size characteristics are quantified based on a sieve analyses of samples which are collected
throughout the project domain. Those samples acquired on the profile between the berm crest (or mean high
water line) and a water depth corresponding to the position of the typical storm bar should be used to
characterize native beach sand for the purpose of assessing the compatibility of sand from potential borrow
sources. Compatibility of borrow and native beach material is primarily based on grain size characteristics,
and to a lesser extent on color. Part V-4-1-e discusses sediment characterization and compatibility of fill in
more detail.
V-4-8
Beach Fill Design
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