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R.H.C. C harlier and Chr. P. De Meyer
Dams and salt water intrusion barriers can protect water supplies and flesh water
habitats. On the negative side, these structures can retain sediments which in turn
can increase erosion of coastal headlands and impair the ability of deltaic
wetlands to keep pace with sea level rise.
In deltaic areas, levees might be constructed along rivers to prevent flooding due
to sea-level rise. The resulting "channelizing" of rivers could, in some cases,
prevent annual river floods from providing sediment and nutrients necessary to
enable deltas to keep pace with sea-level rise and maintain the fertility of
agricultural lands t°.
4.2
Soft Structures
Soft structures have a less severe impact than hard structures, since they usually
consist of simulated natural features, such as beaches and wetlands l~.
The most common "soft engineering" approach is beach nourishment which
involves dredging sand from back bays, navigation channels, or offshore, or
excavating material from a land-based source and placing it on the beach.
Because beach ecosystems are already adapted to annual erosion/accretion cycles,
the placement of sand on the beach generally has little impact on beach
ecosystems. Impact of "profile" feeding is still under study. By contrast, the
dredging itseff can seriously disrupt shallow water ecosystems and wetland
habitats, both due to the direct effects of removing material and the resulting
increase in turbidity.