EM 1110-2-1100 (Part V)
31 Jul 2003
Table V-3-3
Assessment of Commonly Expressed Concerns Related to Coastal Armoring (Dean 1987)
No.
Concern
Assessment
Coastal armoring placed in an area of existing
1
By preventing the upland from eroding, the beaches
True
erosional stress causes increased erosional stress
adjacent to the armoring share a greater portion of the
on the beaches adjacent to the armoring.
same total erosional stress.
Coastal armoring placed in an area of existing
2
Coastal armoring is designed to protect the upland, but
True
erosional stress will cause the beaches fronting the
does not prevent erosion of the beach profile waterward of
armoring to diminish.
the armoring. Thus, an eroding beach will continue to
erode. If the armoring had not been placed, the width of
the beach would have remained approximately the same,
but with increasing time, would have been located
progressively landward (see 2b).
Beaches on eroding coastlines will diminish in front True
2a
An eroding beach continues to erode relative to a fixed
of fixed dune positions.
dune position. The width of the beach must diminish if the
shoreline is eroding (Figure 1).
Natural beaches on retreating barriers maintain
2b
True
Relative to a retreating duneline, a shoreline eroding at the
the same beach width.
same rate results in a stable beach width.
Coastal armoring causes an acceleration of
3
Probably
No known data or physical arguments support this
beach erosion seaward of the armoring.
False
concern.
An isolated coastal armoring can accelerate
4
True
If an isolated structure is armored on an eroding beach,
downdrift erosion.
the structure will eventually protude into the active beach
zone and will act to some degree as a groin, interrupting
longshore sediment transport and thereby causing
downdrift erosion.
5
Coastal armoring results in a greatly delayed
Probably
No known data or physical arguments support this
poststorm recovery.
False
concern.
6
Coastal armoring causes the beach profile to
Probably
No known data or physical arguments support this
steepen dramatically.
False
concern.
Coastal armoring destroys foreshore bar and
6a
Probably
No known data or physical arguments support this
trough features.
False
concern.
Coastal armoring placed well-back from a stable
7
False
In order to have any substantial effects to the beaches, the
beach is detrimental to the beach and serves no
armoring must be acted upon by the waves and beaches.
useful purpose.
Moreover, armoring set well-back from the normally active
shore zone can provide "insurance" for upland structures
against severe storms.
8
Unknown
Seawalls increase the longshore sediment
No known data exists, physical arguments can support or
transport.
discredit this concern. Needs research.
9
Probably
Seawalls cause sand transport a far distance
No known data or physical arguments support this
False
offshore.
concern.
10
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Shore Protection Projects
V-3-31
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