FLOOD08485

• County: Jefferson
• Community: Golden
• Stream Name: Tucker Gulch, Kenneys Run
• Basin: South Platte
• Title: Flood Hazard Area Delineation
• Date: 1/1/1983
• Prepared For: Jefferson County / Arapahoe County
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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rainfall were applied to the IS-minute most intense period of the design storms
based on Area-Depth Curves developed by NOAA. Table III shows typical design
storms used for hydrologic modelling, which do not include the areal rainfall
adjustments.

TABLE I I I
TYPICAL 2-HOUR DESIGN STORr1S
GOLDEN, COLORADO AREA
RAINFALL (INCHES)
(min)
Time 2-year 5-year lO-year 50-year 100-year
5 .02 .03 .03 .03 .03
10 .04 .05 .06 .08 .08
15 .08 .12 .14 .12 .12
20 .16 .21 .26 .19 .21
25 .25 .35 .42 .35 .36
30 .14 .18 .20 .59 .65
35 .06 .08 .10 .28 .36
40 .05 .06 .07 .19 .21
45 .03 .05 .06 .12 .16
50 .03 .05 .05 .12 .13
55 .03 .04 .05 .08 .10
60 .03 .04 .05 .08 .10
65 .03 .04 .05 .08 .10
70 .02 .04 .05 .06 .05
75 .02 .04 .05 .06 .05
80 .02 .03 .04 .04 .03
85 .02 .03 .03 .04 .03
90 .02 .03 .03 .03 .03
95 .02 .03 .03 .03 .03
100 .02 .02 .03 .03 .03
105 .02 .02 .03 .03 .03
110 .02 .02 .03 .03 .03
115 .01 .02 .03 .03 .03
120 .01 .02 .02 .03 .03
Totals 1.15" 1.60" 1.91" 2.72" 2.98"

Depression and detention storage values were obtained from the Urban Drainage
and Flood Control District Urban Storm Drainage Criteria Manual. Values of
pervious and impervious detention varied from 0.3" to 0.4", and from 0.05" to 0.1"
respectively. Infiltration loss rates were estimated based on a preliminary
inventory of soils prepared by the U.S.D.A. Soil Conservation Service (Reference
14). Infiltration losses were based on Horton's Equation using the following
infiltration values and decay rates:

f; = 3.0

f = 0.5
o

0< = .0018

Horton's Equation:

f = fo + (f. - f ) e -..,<, t
1 0

in which,

f = infiltration rate in inches/hour
f. = initial infiltration rate in inches/hour
1
f = final infiltration rate in inches/hour
o
a< = decay coefficient in per second units
t = time in seconds

Imperviousness (Ia) of each sub-Basin was estimated for both existing and future
land use conditions. Future basin conditions were assumed for the hydrology
used in this report. For undeveloped areas the imperviousness was assumed to
be 2%. In the urban areas, the future land use imperviousness was estimated
using aerial photographs along with information regarding projected annexation
plans, the limits of Golden's water distribution system, existing land use
zoning, and proposed development plans. . The future land use condition assumes
maximum development in each sub-basin based upon current planning. The selected
values of Ia were based on criteria recently developed for the City of Louisville
by the Urban Drainage and Flood Control District. la values for each sub-basin
are listed in Table II.

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