FLOOD06459

• Designation Number: 96
• County: Douglas
• Community: Unincorporated Douglas County
• Stream Name: Happy Canyon Creek; Badger, Newlin, Baldwin, Sulph
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Happy Canyon Creek, Badger Gulch, Baldwin Gulch, Sulphur Gulch & Tallman Gulch, Douglas-Araphahoe Counties, CO
• Date: 11/1/1977
• Designation Date: 1/1/1978
• Floodplain - Doc Type: Floodplain Report/Masterplan

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HYOROLOGIC ANALYSIS

TABLE 2

Hydrologic analyses were carried out to establish the peak discharge-

frequency relationships for floods of 10, 50, 100"and 500-year recurrence

intervals for each stream.

RAINFALL DATA

The synthetic hydrograph method was used to obtain the peak rates of

runoff caused by a storm duration of 24 hours and a Type II A dis-

tribution as described in NEH-4. The amount of rainfall was obtained

from precipitation frequency atlas (NOAA Atlas 1973) and areal

adjustment was applied to convert the point precipitation values to

average precipitation over the watershed areas. Values of la, 50, 100

and 500-year peak discharges were obtained using the computer programs

WSP2 and TR20 developed by the Soil Conservation Service.

Drainage Basin Storm Maximum Total Adjusted Rainfall Depth-Inches
Duration 10-yr, 50-y r. lOa-yr. 500-yr.
Happy Canyon Creek 24 hr. 2.9 3.9 4.4 5.6
Badger Gulch 24 hr. 2.9 3.9 4.4 5.6
Newl in Gulch 24 hr. 2.8 3,7 4.3 5,8
Baldwin Gulch 24 hr. 2.8 3.7 4.1 5,2
Sulphur Gulch 24 hr. 2.7 3.7 4.1 5.2
Tallman Gulch 24 hr. 2.7 3.7 4. I 5.2

The calculations were based on rainfall and drainage basin character-

istics appropriate for the study area. A summary of rainfall data

used in the study is provided in Table 2. For the purpose of this

study, the drainage basins are considered to be fully developed

consistent with existing land use and the land use plans of Arapahoe

and Douglas Counties. Other runoff factors were determined by field

reconnaissance.

Typical flood hydrographs for the streams are provided in Figures I
through 3, and Discharge Probability Profiles are provided in Figures
4 through 9. The profiles show the peak discharge at any point within
the stream basins for the 10, 50 and laO-year storm frequencies.
Table 3 lists the discharges at selected reference points.

A complete record of the technical calculations for the hydrologic
analyses is available at the Urban Drainage and Flood Control District.

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