FLOOD00734

• Designation Number: 213
• County: Adams
• Community: Thornton
• Stream Name: Brantner Gulch and Tributaries
• Title: Flood Hazard Area Delineation - Brantner Gulch and Tributaries
• Date: 1/1/1983
• Designation Date: 5/1/1983
• Floodplain - Doc Type: Floodplain Report/Masterplan

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6

Adjacent drainage basins such as the Grange Hall Creek
Basin and the Direct Flow Area 0054 Basin were previously
studied by the Urban Drainage and Flood Control District and
the resultant maps were incorporated into this report to ensure
compatibility of drainage basin boundaries. In addition, a
flood study was performed on the South Platte River in Adams
County by the Urban Drainage and Flood Control District and the
Colorado Water Conservation Board. This study provided information
on the extent of the South Platte River flooding during the
various storm frequencies and their related flood elevations.
This information was used in the preparation of this FHAD report.
The la-year river flood elevation was assumed to be two (2) feet
below the lOa-year flood elevation.

IV. FLOOD HISTORY

Several items of pertinent data were referred to during

the analyses of the gulches. Some of the items were:

a. Current U.S.G.S. topographic and geologic maps

b. plans of existing facilities made available by

Thornton, Adams County and the State Division of

Highways, and

c. projected land use maps

Topographic maps at a scale of 1"=100' and a contour interval

of two feet were prepared by Landmark Mapping Company for this

project. These maps were used to determine the extent of

flooding and to provide a base map for the plan portion of the

plan and profile sheets in this FHAD report.

To the knowledge of the writers and the City of Thornton,
no accurate records of flood history exist for Brantner Gulch
within the Thornton City limits. On occasion, channel flows have
overtopped the roadway at Colorado Boulevard. The potential for
substantial damage in a lOa-year flood unquestionably exists at
this intersection. However, there are no available data
regarding storm magnitudes or degree of damage for the entire
reach length.
County officials reported that two storms in recent history
reveal potential flood hazard areas at the eastern end of the
Gulch in Adams County. The majority of flooding, however,
occurred as a result of high flows in the South Platte River.
In 1965 and 1973, flooding by Platte River flows was observed
at Henderson Road east of the County Golf Course Club House.
In addition, 1973 Platte River flows flooded the County Play-
ground area. Flooding was observed during the 1973 storm in the
northwest section of the County Golf Course, which was a result
of high flows in the Regional Park Tributary channels. County
buildings in the fairgrounds area were not constructed until
1968. Therefore, flooding prior to 1968 cannot be referenced
to county structure locations.
No flood history information was available for the Brantner
Gulch reaches between Colorado Boulevard and Riverdale Road.