EM 1110-2-1100 (Part V)
31 Jul 2003
Alteration/removal costs: The estimated expenses required to alter the design or completely
remove the structure if there are significant, downdrift impacts.
Evidence from postproject monitoring and decision criteria mechanisms
are required for implementation. This cost has been ignored for most
projects and could be included in the category of maintenance costs.
Total, life-cycle cost
The combined initial, maintenance and alteration/removal costs required
over the design life of the project. Annual maintenance costs are usually
converted to their present worth so that they can be directly combined
with the initial construction costs. The present worth (value) is
determined by multiplying the annual maintenance expense by the
present worth factor, PWF. The PWF is a function of the design life and
the interest (discount) rate. (See any standard engineering economics
text).
Design life:
An estimate of the number of years of useful life of the structure/
alternative. Usually 25 to 50 years is employed for well-designed
projects. Design life selection includes structural life of materials
(structural integrity), functional life (usefulness), technical life
(technologically up-to-date), and aesthetics. Design life is employed for
the economic analysis of the present worth of annual maintenance cost
for the total, life-cycle cost comparison of all alternatives. It does not
mean the length of time the project will last in the field.
Interest rate:
The second variable required to calculate the present worth of the annual
maintenance costs. Often, the rate employed is related to the current,
bank loan rate for construction projects. It can also be set by government
policy as discussed in Part V-8 for the Federal government.
Damage:
When energy levels in storms exceed the design levels, both structural
damage and some loss in functional performance may occur. Repair is
possible. Damage is an expected aspect of risk-based coastal design.
Failure:
When storms below the design level cause loss of structural integrity
and/or functional performance. The design has failed and a redesign is
needed before repair or reconstruction. Use of the word "failure" for
loss of structural integrity or performance should be avoided until it can
be proven that a design failure took place under specified storm
conditions.
Balanced design:
The most economical balance between the initial construction costs and
maintenance (damage repair) costs so that the total cost is a minimum.
Initial costs increase as the level of protection for more powerful (but
rarer) storms increases, but maintenance costs decrease because damage
is less frequent. The classical U-shaped, total cost curves result. (See
Part VI-7 for an example with rubble-mound breakwater design)
(b) Benefits. Storm damage reduction and coastal erosion mitigation are the two major benefits of shore
protection. These two along with ecosystems restoration are the only benefits allowed by the Federal
government for Corps projects as discussed further in Part V-8.
V-3-10
Shore Protection Projects
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