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Photo by: Kyla Sheehan

Breakwaters

Breakwaters are large structures often extending
far offshore, and are designed to protect harbours
or areas of the coast from incoming waves and Photo by: Mina Girgis on Unsplash
erosion by longshore drift . These structures are
intended to shield shorelines from the erosive force
of incoming wave energy — however this cuts the
down-current area off from inputs of sediment
normally delivered by longshore drift . Breakwaters
and associated harbours are often areas where
marine debris like logging debris and styrofoam
pieces collect, not to mention harmful gasoline
residues and other boat waste — breakwaters
trap all of these materials within the area, further
reducing the availability of healthy habitat . Harbour
structures also directly impact nearshore habitat
by shading out areas from the sun — this prevents
growth of kelp, seaweeds and eelgrass .

However, while traditional groynes help to maintain
Groynes & Jetties sediment beaches in particular areas (depending
Groynes and jetties are rock walls or berms that are on the materials used), they do not provide habitat,
positioned perpendicular to the shorelines . They and can exacerbate the impacts of erosion down
may or may not be attached to the shoreline, and the shoreline . In contrast, sills are low rock walls
the design and materials used are critical to the constructed parallel to the shoreline . They are often
function of the shoreline . These structures can used to protect beaches from the erosive force
be designed to interrupt longshore currents to of waves by forcing them to crash away from salt
manipulate where sediment is maintained, preserve marsh, or other sensitive vegetation . Like groynes,
beaches and prevent the sand from migrating away sills help to maintain sediment behind them by
from those particular areas . This can be especially reducing wave action at the shoreline . All of
helpful in sediment starved beaches . Where there these structures can be used as part of a beach
are larger structures like breakwaters blocking restoration plan, but they can also cause problems
sediment input to a particular area, these types of by altering the natural processes of sediment
structures can be used to help maintain a beach . transport if not properly designed .

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