GUIDING PRINCIPLES FOR DESIGN
With so many options available, a decision may seem difficult. The following section on
functional design should provide assistance toward a wise choice. At the end of the FUNCTIONAL
DESIGN section, there are summary decision tables, followed by the STRUCTURAL DESIGN section
with important guidelines for planning structures to withstand the forces expected at the site. Finally,
THE CONSTRUCTION STAGE section gives important precautions during actual implementation.
FUNCTIONAL DESIGN
Shoreform Compatibility
Certain approaches are better suited to particular shoreline configurations than others.
It is
important to choose a method appropriate to the dominant shoreform at your site.
Bluff Shorelines. The no action alternative can be appropriate since it does not disrupt the natural
shoreline processes and requires no investment for protective structures. However, the property may
eventually be totally destroyed by erosion. While relocation also does not disrupt shoreline processes and
permanently eliminates any threat to buildings if done properly, it also requires special equipment and
skills and can cost as much as or more than a protective structure. Bulkheads are ideally suited either for
full-height retention of low bluffs or as toe protection for high bluffs. They can be constructed of readily
available materials, are easily repaired if damaged, and are particularly useful with steep offshore slopes.
They can, however, induce toe scour and loss of remaining beach material from the force of reflected
waves. They also have high initial costs and some require special pile driving equipment which may
have difficulty reaching the work site. Revetments are sometimes effective in bluff situations. Low
bluffs that can be regraded to a stable slope may be effectively protected by revetments. Revetments can
protect the toes of high bluffs, either alone or in conjunction with another device. Breakwaters reduce
wave energy reaching the bluff but do not provide positive protection to the toe. They may build or
maintain a sand beach which provides some protection by buffering against normal waves but would be
ineffective against storm waves. They require an adequate sand supply and gentle offshore slopes.
Groins provide only a buffer by building or holding a beach. Since they require a natural sand supply,
they would generally not work in a clay or silt bluff area unless sand were imported. Beach fills provide
only dissipation of normal wave action and would not be effective during severe storms. Vegetation
provides little protection until well established and, even then, does not positively protect against large
storm waves. Drainage controls are mandatory if groundwater and seepage adversely affect slope
stability. They provide no toe protection against wave action and can be expensive. Also, they are
difficult to properly design and require the assistance of a qualified engineer. Slope flattening provides a
permanent solution for slope stability problems but does not provide protection against continued wave
action. It also requires adequate setback room at the top of the bluff for the slope. Perched beaches
would protect the bluff from normal wave action but would not provide positive toe protection during
storms. A combination approach can be the best solution. For instance, drainage controls should be used
as needed, possibly with slope flattening as well. Toe protection could be provided with a revetment
along with a fronting sand beach for additional protection (provided offshore slopes are mild).
Vegetation planted on the regraded slope would prevent erosion from runoff and also help to stabilize a
beach fill.
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