FLOOD01193

• Designation Number: 61
• County: Adams
• County: Arapahoe
• County: Douglas
• Community: Denver Metro Region
• Stream Name: Goldsmith Gulch and Tributaries
• Title: FHAD - Goldsmith Gulch and Tributaries, Metropolitan Region, Colorado
• Date: 6/1/1976
• Designation Date: 11/1/1976
• Floodplain - Doc Type: Floodplain Report/Masterplan

4

- FLOOD RELATED STUDIES AND OTHER PERTINENT DATA -

One previous flood study has been prepared for Goldsmith Gulch
by the U. S. Army Corps of Engineers.2 The study was prepared
as part of a Flood Plain Information Report for the Denver metro-
politan region. This study outlined the 100-year and standard
project floods based on the basin development conditions projected
to 1980. The study also estimated that the I-225 embankment would
reduce the 100-year flood peak approximately 35 percent. This is
not the case, and, as a result, the flood peak for the ultimately
developed basin is approximately 65 percent larger than the dis-
charge predicted by the Corps in 1971. In addition, channelization
and future development beyond that predicted for 1980 cause the
increase in the 100-year flood flow above that reported in the 1971
USACE study.

3
Runoff Information Report. A summary of the rainfall data used
in the study and the drainage basin characteristics is provided
in Tables 2 and 3, respectively. The subbasin boundaries are
shown on Sheet 2 of 20, Basin Boundaries.

Varying rainfall intensities were assumed to occur in each basin.
Table 2 lists the maximum rainfall depths for each storm frequency
for a 2-hour duration storm. An infiltration rate of 0.5 inches
per hour was utilized in all of the study basins. The runoff
computations included considerations of the percentage of water-
sheds developed and planned future development, as determined by
field reconnaissance and information from the City of Denver, City
of Greenwood Village and Arapahoe County.

Preliminary data on the Flood Hazard Area Delineation study for
Cherry Creek, as prepared by the Urban Drainage and Flood Control
District, has been used to determine the extent of flooding at
the confluence of Goldsmith Gulch and Cherry Creek.

Table 2

Rainfall Data

Maximum, Total Rainfall Depth Inches*

- HYDROLOGIC AND HYDRAULIC DETERMINATIONS -

2-Yr. 10-Yr. 100-Yr.
Goldsmith Gulch 1.2 2.6 3.3
Southmoor Park Tributary 1.2 2.6 3.3
West Tributary-Arapahoe Co. 1.2 2.6 3.3

Hydrologic Analysis

A hydrologic analysis was completed to establish the peak discharge
frequency relationships for floods of 2-, 10- and lOO-year re-
currence intervals.

2. Flood Plain Information Report, Goldsmith Gulch, Dutch Creek,
Lilley Gulch and Coon Creek, Volume VIl U. S. Army Corps of
Engineers, Omaha District, October, 1971. Denver Metropolitan
Region.

*Storm Duration, 2 hrs.l T4 and 5 S., R67W
Ref: Rainfall/Runoff Information, Project REUSE,
UD&FCD, May, 1972.

Typical flood hydrographs for the gulch are provided in Figures
1 and 2. Discharge Probability Profiles for Goldsmith Gulch
and the two tributaries are provided in Figures 3 and 4. This
chart relates the peak discharge at any point within the basin
for the 2-, 10-, and 100-year storm frequencies. Table 4 lists
the flood frequencies and discharges used for the gulch and
tributaries at selected reference points.

The Colorado Urban Hydrograph Procedure, as outlined in the Urban
Storm Drainage Criteria Manual, was used to determine the peak
discharges for each storm frequency. The calculations used rainfall
data characteristic of the study area and provided in the Rainfall/

3. "Rainfall/Runoff Information", Project REUSE, Final Report,
DRCOG and UD&FCD, ,May, 1972.