EM 1110-2-1100 (Part V)
31 Jul 2003
(4) Wetlands. The final alternative in this section on shoreline stabilization structures are fringe marshes
or wetlands. Part IV-2-11 considers their values, distribution classification sediment characteristics, and
causes for loss of wetlands in the coastal zone. However, little is known about their importance for shoreline
erosion mitigation.
(a) Tidal creeks with fetch exposures less than 0.5 nautical miles and low wave-energy environments
can naturally sustain a sufficiently wide marsh fringe. Also, they generally have little or no problem with
upland bank erosion because the established marsh fringe absorbs most of the wave energy before it can
impact the upland area (Hardaway and Byrne 1999). On the Chesapeake Bay, Hardaway and Anderson
(1980) found that low, upland banks erode almost twice as fast as marsh shorelines with similar fetch
exposures and nearshore depths.
(b) Some recent field and laboratory research has focused on wave attenuation by wetland vegetation
(Kobayashi, Raichle, and Asano 1993; Wallace and Cox 1997; Tschirky, Turke, and Hall 2000). Wave
heights are typically reduced by 50 percent and the peak spectral period also drops as the spectrum becomes
more broad banded with higher frequency components. No significant design guidance on allowable wave
heights or currents for wetlands presently exists. The Wetlands Engineering Handbook (Olin, Fischenich,
and Palermo 2000) provides a wealth of valuable information for the restoration and creation of wetlands.
V-3-4. Nonstructural Alternatives
a. Introduction.
Nonstructural alternatives are management strategies for coastal hazard mitigation that are not armoring
(Part V-3-2) nor beach stabilization structures (Part V-3-3), nor beach nourishment (Part V-4). Society has
developed ways to adapt by setting requirements for the elevation of buildings, providing insurance and
planning for continual erosion with setback limits for new construction. The final nonstructural alternative
is to retreat by relocation, abandonment, or demolition.
Three Federal government agencies (the USACE, Federal Emergency Management Administration
(FEMA), National Oceanographic and Atmospheric Administration (NOAA)) with different
missions, planning methods, and requirements for benefits determination employ or promote the use
of nonstructural methods. This section briefly summarizes the role of each and presents some
examples of the retreat alternative. Full details of the Federal government's planning requirements
and design constraints for all three agencies involved are presented in Part V-8.
Coastal hazard mitigation is addressed in a piecemeal manner by multiple agencies within states, at
the county, city and community level, and by businesses and individuals operating and living at the
water front. Property ownership (Federal, state, municipal, community, and individual) and the value
of scarce waterfront property strongly motivates all parties to protect their valuable investments. Part
V-8 presents details of how each Federal agency (CORPS, FEMA, and NOAA) interacts with each
level of responsible group, but details of approaches by these parties are beyond the scope of this
chapter.
b. Adaptation.
(1) Zoning and building codes. Any structural or nonstructural change in the design, construction or
alteration of a building to reduce damage caused by flooding and flood related factors (storm surges, waves,
and erosion) is considered a flood proofing alternative by FEMA. The mechanism to require change in old
construction practices is the National Flood Insurance Program (NFIP) administered by FEMA using Flood
V-3-80
Shore Protection Projects
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