FLOOD00689

• Designation Number: 136
• County: Arapahoe
• Community: Littleton
• Stream Name: Slaughterhouse Gulch
• Title: Major Drainageway Planning - Slaughterhouse Gulch, Littleton
• Date: 5/1/1974
• Designation Date: 5/1/1979
• Floodplain - Doc Type: Floodplain Report/Masterplan

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SECTION V
FLOOD DAMAGE - BENEFIT ANALYSIS

The flood damage or benefit analysis is one part of the benefit/
cost evaluation completed in the Slaughterhouse Gulch planning
work. Benefits are generally described as the reduction in
potential damage resulting from improvements or actions taken to
improve the facility under consideration. In connection with
Slaughterhouse Gulch, the benefits considered are those which
would be derived from the expenditure of a certain sum of money
in improvements or from the results of land use controls, which,
in effect, would reduce the potential damage due to flooding
under the existing channel conditions.

The theory behind the benefit evaluation and the total benefit/
cost analysis procedure, as well as the application to urban
storm drainage projects, is well covered in the text, Economics
of Water Resources Plannin~, by L. Douglas James and Robert L.
Lee, pub11shed by McGraw Hlll in 1971.

~

The first step in completing a benefit evaluation is the deter-
mination of the existing damage potential for a stream. This
is done by computing the water surface profiles for a minimum
of three flood events. Using depth-damage relationships char-
acteristic of the area within the flood plain, the dollar damage
figures for each storm event are calculated and plotted on a
graph of dollar damage versus percent probability or return
frequency of the storm event. Evaluating the area beneath the
plotted curve gives the average annual damage potential charact-
eristic of the channel reach under consideration. This was the
procedure followed in the determination of the damage potential
characteristic of Slaughterhouse Gulch.

To simplify the determination of property damages associates with
flooding, one depth-damage curve for single family residential
property was derived. The typical house type was considered to
be a multi-level design with a walk-out basement level and a
foyer entrance. From assessed evaluations available in the
areas adjoining the gulch, the average value of the houses and
property was assumed to be $32,200. Subtracting an assumed lot
value of $7,000 from the assessed evaluation gave an average
structural value of approximately $25,200. Similar figures were
determined for apartment houses and commercial structures.

The contents of each housing unit were set at $8,000 per unit.
Using these values and the depth-damage curves developed by the
Corps of Engineers for the Federal Insurance Administration as
a basis, a special depth-damage curve was determined for
Slaughterhouse Gulch. Computing damages was then a matter of
determining the number of houses flooded and the depth of inun-
dation.

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