FLOOD06042

• County: Denver
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: Colorado Landslide Hazard Mitigation Plan
• Date: 1/1/1988
• Prepared For: State of Colorado
• Prepared By: CGS
• Floodplain - Doc Type: Educational/Technical/Reference Information

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THE COST.BENEFIT 6F MITIGATION

Costs of Landslidin9

The Committee on Ground Failure Hazards (1985)
estimates that economic losses of at least $1 to $2
billion and 25 to 50 deaths occur each year in the United
States as a result of landsliding. Economic losses in-
clude direct and indirect costs. Schuster and Fleming
0986, p. 12) define direct costs as "the costs of
replacement, repair, or maintenance due to damage to
installations or property within the boundaries of the
responsible landslide." They list indirect costs as:
I) reduced reaI-estale values in areas threatened by
landslides.
2) loss of productivity of agricultural or forest lands.
3) loss of agricultur:al or industrial productivity as a
result of damage to land or facilities or interruption
of tr.msportation systems,
4) loss of tax revenues on properties devalued as a
result of landslides,
5) costs of measures to prevent or mitigate additional
landslide damage,
6) advene effects 01\ water quality in streams and ir-
rigation facilities outside the landslide limits.
7) secondary physical effects, such as Iandslide-caused
Hooding, fur which the costs are both direct and in-
direct, and
8) loss of human productivity due to injury or death.

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In addition, there are intangible costs such as stress,
reduced quality of life, and the destruction of personal
possessions with only sentimental value. Because costs
of indirect and intangible losses are difficult or impossi-
ble to calculate, they are often undervalued or ignored.
The rising event-specific and cumulative costs of Iand-
sliding are a direct consequence of the ,increasing
vulnerability of populations to the hazard. In most
regions, the overall rate of occurrence and severity of
naturally-caused landslides has not increased. What has
increased is the extent of human occupation of marginal
lands and the impact of human activities on the environ-
ment. Increasingly, hazard-mitigation techniques are be-
ing used to overcome objections to development of
marginal land.
When extensive development of marginal or potential-
ly hazardous land is proposed, a cost -benefit analysis
should be performed to determine if mitigation is
justifiable and cost effective. Frequently, when an ac-
counting is made of the potential costs and benefits of
development in a hazardous area, the costs may
outweigh the benefits over the long term. The cost of
mitigation should be considerably less than, or at least
equal to the total value of the property to be protected.
However, in cases of existing development, where
human lives are threatened, strict economic considera-
tions may have to be ignored.
Petak and Atkisson 0982, p. 171) use "break-even"
damage rates to identify projects where mitigation might

be considered feasible. They list the following five

values as necessary for determination of the break-even

rate:

I)
2)

3)

the initial cost of the ming,mnn:
the annual expected loss reductioo associated with
the mitigation:
the period of time over which costs are to be amor-
tised and loss reductions are to be experienced;
the tota1 estimated loss reductioo that wiD be pr0-
duced by the mitigation over the lifetimes of
bui1dings on areas to which the mitigation is applied:
[and]
either the discount llIIe that is applied to building-
life loss reductions, or the building life accumulated
annual amortized costs of the mitigation at a
specified interest Iate.

4)

5)

Economic Payoffs from Landslide Hazard
Mitigation

Studies have been conducted to estimate the potential
savings when measures to minimi7.e the effects of Iand-
sliding are applied. One early study by Alfors, Burnett,
and Gay (1973) attempted to forecast the potential costs
of landslide hazards in California for the period
1970-2000 and the effects of applying mitigation
measures. Under the conditions of applying all feaSIble
measures at state-of-the-art (for the 197Os) levels, there
was a 90 percent reduction in losses for a benefit/cost
ratio of 8.7:1, or $8.7 saved for every $I spent. Other
studies by Leighton (1976) have shown higher ratios.
The benefit/cost ratio becomes better as the property
becomes more hazardous and/or the density of the
threatened population/structures becomes greater.

Cost-Benefrt Analysis
This method is used by engineers, economists, and
planners to evaluate the feaSIbility of urban drainage and
flood control projects, but can be used equally well for
any contemplated project using structura1 methods. A
cost-benefit analysis enables engineers and/or planners
to make rational choices among structura1 alternatives
by determining whether, over the life of a structure, the
value of the property and/or lives and/or services pro-
tected is equal to or greater than the cost of the
structure.
F"1rst, objectives DD1st be determined. Examples of
objectives are to:
. reduce damage and maintenance requirements to
public and private property and facilities,
. enhance the value of land and other property in
the area,
. reduce threat to life,
. reduce public inconvenience,
. reduce traffic hazards, and
. enhance emergency vehic1e movement.

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