THE DESIGN PROBLEM
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 the site.
Bluff Shorelines. The no action alternative can be appropriate for bluffs since it does not disrupt
natural shoreline processes and requires no investment for protective structures. Eventually, however,
the property may be totally destroyed by erosion. While relocation does not disrupt shoreline processes,
and it can permanently eliminate any threat to buildings, it 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. Constructed of readily available materials and easily repaired if damaged, they are
particularly useful where offshore slopes are steep. They can, however, induce toe scour and loss of
beach material. Revetments are marginally effective in bluff situations. Low bluffs that can be flattened
to a stable slope may be effectively protected by revetments, but high bluffs generally cannot be
regraded. 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 toe protection.
They may build or maintain a beach (if an adequate sand supply exists), which provides some protection
against normal waves, but would be ineffective against storm waves. Use of breakwaters generally
requires gentle offshore slopes. Groins protect only to the extent they can build or hold a beach. Since
they require a sand supply, they would not work in an area of clay or silt bluffs unless sand was imported.
Beach fills provide some protection against normal wave action but would be ineffective during storms.
Vegetation would provide little protection until well established and even then, does not positively
protect against large storm waves. Drainage controls are mandatory if groundwater adversely affects
slope stability. However, they provide no toe protection and can be expensive. Slope flattening provides
a permanent solution for slope stability problems, but does not protect against continued wave action. It
also requires adequate room at the top of the bluff for the slope. A perched beach would protect against
normal waves but would be ineffective during storms. A combination approach can be the best solution.
For instance, drainage controls should be used as needed, possibly with slope flattening. Toe protection
could be provided with a revetment and a fronting sand beach to provide additional protection (provided
offshore slopes are mild). Vegetation planted on the regraded slope would prevent erosion from runoff,
and other species could be used to stabilize the beach fill.
Sand Beaches. The no action and relocation alternatives are applicable as they were for bluffs.
Bulkheads are generally inappropriate unless an elevated feature, such as a promenade or parking lot, is
needed. Vertical bulkheads induce toe scour and wave reflections, and could cause erosion of the beach
fronting the bulkhead. Revetments are better for protecting features directly behind the beach since they
absorb wave energy better and are more flexible when settlement occurs. They have an adverse aesthetic
effect on the beach, however, and they can limit use or access to the shore. Use of revetments by a single
landowner is often a problem because they are subject to flanking. Breakwaters are also well suited
because they trap and hold sand moving along, on or offshore. They can cause extensive downdrift
damages, however, because the trapped sand cannot reach adjacent beaches. They are also expensive to
build. Groins can effectively build beaches on their updrift sides but can also cause accelerated downdrift
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