abrasion by windblown sand particles. Used to trap sand and stabilize the beach, upland vegetation also
improves the beauty of a shoreline, prevents erosion during heavy rain, diminishes the velocity of
overland flow, increases the soils infiltration rate, and provides a habitat for wildlife.
Even though vegetation provides significant help in stabilizing slopes and preventing erosion,
vegetation alone cannot prevent erosion from heavy wave action or prevent movement of shoreline bluffs
activated by groundwater action. In those instances, structural devices augmented with vegetation are
recommended.
The effectiveness of vegetation is also limited by characteristics of the site. For instance, the site
requirements which determine the effectiveness of a tidal marsh planting include: elevation and tidal
regime, which determine the degree, duration, and timing of plant submergence; slope of the site;
exposure to wave action; type of soil; salinity regime; and oxygen-aeration times. Plants which are
specially adapted for higher beach elevations must tolerate rapid sand accumulation, flooding, salt spray,
abrasion by wind-borne sand particles, wind and water erosion, wide temperature fluctuations, drought,
and low nutrient levels. Appropriate species also vary with geographical location, climate, and distance
from the water (vegetative zone).
INFILTRATION AND DRAINAGE CONTROLS
Infiltration and drainage controls are often needed to achieve stability along high bluff shorelines.
Although many factors lead to slope stability problems, the presence of groundwater is one of the most
important, since the majority of slope failures and landslides occur during or after periods of heavy
rainfall or increased groundwater elevations. Infiltration controls prevent water from entering the
ground, while drainage controls remove water that is already present in the soil.
Infiltration can be controlled by appropriate ditches and swales, and by sealing the ground surface.
Surface cracks that develop when a slope begins to fail can be an easy path for water to enter, exert
hydrostatic pressures, and lead to further instability. Such cracks should be promptly filled with
compacted, relatively impermeable soil (preferably clay) to reduce the potential for such detrimental
effects.
Drainage of the subsurface can be accomplished using vertical or horizontal drains. Standard
design techniques and methods are described in civil engineering references such as Winterkorn and
Fang (1975).
SLOPE FLATTENING
A bluff slope may be flattened to enhance its stability when adequate room exists, and there is no
interference with the desired land use. Freshly excavated slopes should be planted to prevent erosion
from surface runoff. It may also be necessary to build a revetment or bulkhead at the toe of the slope to
protect against wave action.
PERCHED BEACHES
A perched beach (Figure 11) combines a low breakwater or sill and a beach fill perched, or elevated,
above the normal level. This alternative provides a broad buffer against wave action while offering a
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