FLOOD07168

• County: Jefferson
• Community: Golden
• Basin: South Platte
• Title: Flood Insurance Study - City of Golden
• Date: 11/18/1984
• Prepared For: Jefferson County
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

of the elevations of floods of the selected recurrence intervals
along each of these flooding sources.

Water-surface elevations of floods of 10-, 50-, 100-, and 500-
year recurrence intervals were computed using the U.S. Army Corps
of Engineers HEC-2 step-backwater computer program (Reference 16).

The cross sections used in the backwater analyses of the streams
in Golden were obtained from a number of sources. Cross sections
on Clear Creek were compiled by Bell Mapping Company using photo-
grammetric methods for the flood hazard area delineation by Gingery
and Associates, Inc. (Reference 17). Cross sections on Tucker
Gulch, Cressmans Gulch, Cressmans Gulch Old Channel, Kenneys Run,
East Fork Kenneys Run, West Fork Kenneys Run, West Fork Kenneys
Run Tributary No.1, North Fork of West Fork Kenneys Run Tributary
No.1, West Fork Kenneys Run Tributary No.2, and Deadman Gulch
were digitized by photogrammetric methods using aerial photographs
at a scale of 1:6,000 (Reference 18). Cross sections on Apex,
Jackson, and Lena Gulches were compiled by the Olympus Mapping
Company for a report by Wright-McLaughlin Engineers, by photogram-
metric methods, using maps at a scale of 1:1,200, with a contour
interval of 2 feet (Reference 15).

Locations of selected cross sections used in the hydraulic analyses
are shown on the Flood Profiles (Exhibit 1). For stream segments
for which a floodway is computed (Section 4.2), selected cross
section locations are also shown on the Flood Boundary and Floodway
Map (Exhibit 2).

Data for the bridges, culverts, and other hydraulic structures
in Golden were obtained from a number of sources. The data for
all detailed-study streams except Clear Creek and Apex, Jackson,
and Lena Gulches were obtained from field surveys. The data
for Clear Creek were furnished by Bell Mapping Company and Norman
Associates for Gingery and Associates, Inc. (Reference 17). The
data for Apex, Jackson, and Lena Gulches were furnished by Olympus
Mapping Company for a report by Wright-McLaughlin Engineers (Refer-
ence 15). All hydraulically significant structures were field
checked to verify elevation data and structural geometry, and
modifications have been made where significant changes have occurred.

Channel roughness factors (Manning's "no values) typically ranged
from 0.025 to 0.040 in the channels, with lower values (from 0.015
to 0.025) for concrete structures and culverts and higher values
(from 0.040 to 0.080) for reaches obstructed by vegetation. On
the overbanks, the "no values typically ranged from 0.030 to 0.040,
with lower values (from 0.015 to 0.030) for asphalt and undeveloped
areas and higher values (from 0.040 to 0.20) for vegetated or
developed areas. These values were obtained using engineering
judgment and field inspection of the study areas.

15