FLOOD01607

• County: Gilpin
• Community: Central City
• Stream Name: Eureka and Nevada Gulches
• Title: Master Drainage Study
• Date: 2/12/1988
• Prepared For: Central City
• Prepared By: HydroDynamics
• Floodplain - Doc Type: Floodplain Report/Masterplan

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CENTRAL CITY MASTER DRAINAGE STUDY

32

SECTION 7. ECONOMIC ANALYSIS

Economic analyses for drainage can be very complex. Many factors
are considered, in addition to real property value, such as the
value of lost lives, lost wages, lost commercial income, cost of
detour driving while streets are flooded, cost of time while
driving that detour, increased exposure to accidents while
driving the (longer) detour, etc. can be considered.

In the cases of Eureka and Nevada Gulches, however, a simplified
approach considering only building damage is sufficient to
demonstrate the benefit created by expenditure of publ ic funds
for drainage construction. This simplified analysis is
particularly well suited to Central City because of the valuable
historical buildings that are in the path of flooding, the
inadequate major drainage system and the relatively low cost of
construction. The approach accounts for probabilities associated
with levels of flooding and annualized risk of damage to property
associated with those probabilities.

Table 7.1.1 is a partial list of buildings that are in the path
of flooding as defined by CWCB (1987). The total assessed values
of buildings subject to flooding is $4,293,200 and $1,343,800 for
Eureka and Nevada Gulches , respectively (Nights of Phythias is
counted in both Eureka and Nevada Gulch totals1.

Damage to real properties was calculated for the following
conditions:

1. overtopping the Opera House flume causes street
flooding,

2. street flooding recurrence intervals for existing and
improved conditions are 2.6 and 13 years, respectively,

3. street flooding causes five percent damage to
structures and contents (this is generally modeled
after Federal Emergency Management Agency data supplied
to the author by CWCB, that averages 6.3 percent damage
to structure and contents per foot of depth plus
velocity head),

4. double the assessed value to account for a higher-than-
assessed market value (e.g., the Golden Rose is
assessed at $283,000 and is presently on the market for
more than $750,000),

5. all buildings listed in Table 7.1.1 are inundated to a
depth of one foot (some buildings will be inundated
more, some less),

6.

no additional damage occurs
flooding (for simplicity
conservative results).

for greater depth of
of calculation and

HydroDynamics Incorporated