A LOOK AT THE OPTIONS
Three basic choices are possible in response to an erosion problem: no action, relocation of
endangered structures, and positive corrective measures. The latter includes devices that directly armor
the shore, those that intercept and dissipate wave energy, and those that retain the earth slopes against
sliding. Each alternative requires an evaluation of the planned land uses, money and time available, and
other effects that may result from the decision.
NO ACTION
This is a decision-aid that can be used to evaluate different alternatives. Because even low cost
solutions can require substantial investments, it is preferable to closely estimate potential losses using
this alternative, particularly if no dwellings are directly threatened, and only undeveloped land or
inexpensive structures are in danger. Also, erosion problems are sometimes caused by temporary factors
(e.g., unusually high Great Lakes levels) that may abate. The resulting erosion, therefore, may slow
before any action is taken. This could eliminate the immediate need for protective devices, or it could
mean choosing a smaller scale, less expensive, device.
RELOCATION
In most cases, some action is necessary. It may be less expensive to relocate endangered structures
than to invest in shore protection. Relocation can be to an entirely different site or it can be a setback
farther from the water at the present site. The required setback must be carefully evaluated because the
considerable expense of moving a building could be wasted if the setback is insufficient.
The first step is to evaluate the long-term erosion rate. This is difficult because reliable historical
data on past shoreline positions is often lacking. Possible sources of data include a time sequence of
aerial photographs or shoreline maps. If the property owner has occupied the site for many years (say 25
or more), and has observed slow shoreline retreat during that time, the annual erosion rate could be
approximated by dividing the total amount of retreat by the number of years of observation. For instance,
if the shoreline steadily receded 300 feet in 30 years, the estimated average erosion rate is about 10
feet/year. A setback of 100 feet could produce an additional 10 years of life for a structure, provided
erosion continues at the same rate.
Conversely, if the shoreline was stable for years and suddenly retreated 300 feet in only 5 years,
relocation on the same site may be risky and not generally advisable unless considerable setback room is
available.
BULKHEADS AND SEAWALLS
The terms bulkhead and seawall are often used interchangeably. In a strict sense, however,
bulkheads are retaining walls whose primary purpose is to hold or prevent sliding of the soil while
providing protection from light-to-moderate wave action. Seawalls, on the other hand, are structures
whose primary purpose is to protect the backshore from heavy wave action. Their massive size generally
places them beyond the low cost range. Also, they are not generally needed in sheltered waters where
large waves are not generated (except perhaps in the Great Lakes).
Bulkheads can be used to protect eroding bluff s by retaining soil at the toe, thereby increasing
stability, or by protecting the toe from erosion and undercutting. They are also used for reclamation
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