Groins can be built either high or low with respect to the existing beach profile. High groins
effectively block the supply of sand to downdrift beaches, provided sand cannot pass through them. Low
groins, built to be overtopped by waves either during storms or at a given tide level, permit sand to pass
over them and nourish downdrift beaches.
A groin's length must be sufficient to create the desired beach shape while still allowing sand to
pass around its outer end. If a groin extends seaward past the breaker zone, the sediment moving around
the structure may be forced too far offshore to return to the adjacent downdrift beach. If it is too short, it
may not trap enough sand to provide the desired beach.
The correct spacing of individual groins within a field is often difficult to determine and is a
function of their length and the desired final shoreline shape. If groins are too far apart, excessive
erosion can occur between them. If spaced too closely, they may not function properly. This is
particularly true for long groins where sand passing around their ends must follow a curved path back to
the beach. If the groins are too close together, the sand will be unable to reach the beach before it is
again forced seaward by the next downdrift groin.
A groin must be built to resist wave forces, currents, the impact of floating debris, and earth
pressures created by the difference in sand levels on both sides. As with other structures, groins must
resist toe scour, and must be constructed to prevent failure due to flanking (erosion at their landward
end).
BEACH FILLS
Beach fills are quantities of sand placed on the shoreline by mechanical means, such as dredging
from offshore deposits or overland hauling by trucks. The resulting beach provides some protection to
the area behind it and also serves as a valuable recreational resource.
The beach fill functions as an eroding buffer zone. Its useful life will depend on how quickly it
erodes; a rapid succession of severe storms can completely eliminate a new fill in a short time. The
owner must then be prepared to periodically renourish (add more fill) as erosion continues. Beach fills
generally have relatively low initial costs but periodic maintenance costs needed for adding new fill.
VEGETATION
A planting program to establish desired species of vegetation is an inexpensive approach to
shoreline protection and erosion control. Depending on where stabilization is desired, species from one
of two general groups should be selected to insure adequate growth.
Found on parts of shorelines flooded periodically by brackish water, species of grasses, sedges,
and rushes occur in marshes of moderate to low energy shorelines. Once extensive and widely
distributed, marsh areas were viewed in the past as useless and were subjected to filling and diking.
However, their destruction has lessened as their importance in the ecosystem and to shoreline protection
has been realized.
Upland species (shrubs and trees but particularly grasses) are especially adapted to growing in the
low-nutrient, low-moisture environment of the higher beach elevations, where they are subject to
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