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Seawalls & Bulkheads
Seawalls and bulkheads are hard walls usually
made of concrete that limit how far the tide can
reach along the shoreline . They are often used
along the boundaries of a property in an attempt
to protect the home from incoming waves .
Seawalls do not dissipate wave energy, instead
they reflect it, often resulting in scour at the toe
of the structure and increased wave height and
runup at the wall . By acting as a hard boundary to
the beach, seawalls interrupt the natural process of
waves slowing down and crashing onto the beach .
Instead, incoming waves are forcibly stopped so
that the wave energy is directed vertically - both
up the wall, splashing towards coastal homes, and
down, eroding away sediment from the beach
(Figure 5 .1) . When waves crash into hardened
shorelines, the energy of the water is accentuated
resulting in higher wave heights that can overtop
the seawall during storm events .
Although seawalls may protect an individual Figure 5.1 – Impacts of shoreline modification, such
property, there are many drawbacks . These as this seawall, include benthic scouring, deflected
structures cause the wave energy to be deflected wave energy, habitat loss, and risks of flooding to the
to another part of the shoreline, blocking the properties they are supposed to protect.
natural movement of sediment, and exacerbating Illustration by: Holly Sullivan
erosion elsewhere . The unintended diversion
of waves could result in flooding on other
properties . Seawalls also support 23% lower Coastal Development
biodiversity and 45% fewer organisms than
natural shorelines (Gittman et al . 2016) . Hardened Development in coastal areas can also disrupt
shorelines can even break or flood during storms natural shoreline processes . In developed areas
and other high wave energy events, causing there is typically a net loss of tree canopy and other
serious damage to the structure and putting vegetation . Intact vegetation keeps sediment in
those behind it at risk . place and allows rain to soak in . When vegetation
is cleared for building, erosion can be a significant
These structures also worsen a phenomenon
known as coastal squeeze . Coastal squeeze is problem . If worksites are not managed properly,
the loss of intertidal habitat as sea levels rise . additional inputs of sediment can flow to and be
When the zone above the high-water line is deposited along the shoreline . Even after a building
constrained by hard modifications, the shoreline has been completed there is still a risk of sediments
and habitats are not able to move landward being washed away until landscape vegetation
and naturally adapt to changing sea levels . becomes established . The additional sediments
This effectively shrinks the intertidal area that that wash away from developed areas can bury the
is key to many shoreline organisms . existing sediment on the beach . This has impli-
cations for the critters that live along the shore,
including deposited fish roe . Another consequence
of coastal development is increased impervious
surfaces, such as pavement, roads and roofs, that
can accelerate waterflow into streams and coastal
areas . During stormwater runoff events currents can
be altered and may carry away natural sediments as
Photo by: Maria Catanzaro
well as pollutants from these developed areas .
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