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Page Title: Potential Nearshore Placement Benefits
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Technical Note DOER-N3
March 1998
maintenance dredging can, for illustration purposes, be separated into dredging and disposal costs,
the latter of which is the focus of this technical note. Much of the cost of disposal is a function of
time (e.g., time for a hopper dredge to transit to/from an offshore disposal site). The farther a hopper
dredge has to travel during the dredge cycle, the more fuel that is consumed, and the longer it takes
to dredge a project. Nearshore placement of mixed dredged material, in many cases, would reduce
transit times for hopper dredges and possibly reduce pumping distance for some pipeline dredges,
both of which would result in reduced costs.
In addition, nearshore placement has applications
Potential Nearshore Placement
as a beneficial use approach, as material that tradi-
Benefits
tionally is placed offshore and lost to the local
Supplements beach profile by adding
littoral zone now would be kept nearby and possibly
material to the littoral zone
enhance nearshore profiles and/or beaches. Near-
Renourishes beach
shore placement could also offer a link between the
Decreases nearshore wave heights, thereby
often independent channel dredging activities and
reducing damage from erosive waves and
beneficial use (e.g., beach nourishment) activities.
storms
By linking these activities, interactive project de-
Provides fisheries habitat
sign is facilitated, and both navigation and beach
Reduces use of limited-capacity upland and
offshore disposal sites
use interests can collectively identify a least-cost
Decreases mobilization/demobilization costs
dredging and nearshore placement solution benefit-
Shortens haul distance for hopper dredges
ting all parties. Potential benefits from nearshore
and shorter pumping distance for pipeline
placement of mixed sediments are provided in the
dredges
adjacent table.
NEARSHORE PLACEMENT OBJECTIVE: Initially, planners and designers must decide on
the objective of the nearshore placement. Objectives of nearshore placement of dredged material
vary from simply placing the material in the littoral zone to "feed" the littoral system to designing
and constructing a nearshore berm feature that attenuates waves or serves as a habitat.
Commonly, nearshore placement involves design and construction of a nearshore berm or mound.
Typically, finer grained sediments (which are less desirable on beaches) placed with hopper dredges
or barges (from clamshell/bucket dredges) are used to construct "stable" berms in deeper water. If
the berm relief is sufficiently tall compared with the water depth and local wave climate, stable
berms can reduce wave energy on their lee. For "feeder" berms, material more closely resembling
native sands is used to match local beach sand and/or nearshore sand. Nearshore placement (in the
form of berms) can also serve as fish habitat. Design guidance of nearshore berms was developed
under the WES Dredging Research Program (DRP) and is provided in McLellan (1990a, b), Burke
and Allison (1992), and Pollock and Allison (1993). For illustration, an analytical study (using the
DRP guidance) was conducted to determine the economic feasibility of a nearshore berm
alternative for the St. Johns County, Florida, Beach Erosion Control Project. This effort is
described in Pollock, Curtis, and Moritz (in preparation).
In some cases, a designed "berm" may not be desired or cannot be constructed with available
material. However, nearshore placement may keep material in the local littoral zone to facilitate
marsh creation (or slow marsh degradation) or act sacrificially in lieu of nearby beaches or marshes.
2

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