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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2$

The Thornton City Council, in March of 1982, voted to retain

Eastlake Dam No. 2 and Reservoir as a flood detention dam. This

dam is in need of improvements in order to meet the State

Engineer's requirements for dams.

The open earth discharg~ channel from Dam No. 2 has

sufficient capacity for the Dam No. 2 discharge and local

runoff from the lOO-year storm until it nears Steele Street.

At this point the undersized culverts under Steele Street and

East l24th Avenue combined with local runoff from the drainage

area to the south, result in an overflow of the channel banks

west of Steele Street. Only one small building is in the flood-

plain in this area.

East of Steele Street to Monroe Street the flooding is

widespread because the existing open earth channel does not have

sufficient capacity for the lOO-year storm runoff. The area

between Steele Street and Mon~oe Street is undeveloped at the

present time.

Discussion of Eastlake Dam No. 3 is continued in the
description of Brantner Gulch Tributary V.
The combined flows from Eastlake Reservoir No. 2 and No.3,
and from local rainfall runoff create widespread flooding north
of l24th Avenue from east of Monroe Street to just west of Colo-
rado Boulevard. The open earth roadside ditch in this portion
of the Reach has insufficient capacity to contain the lOO-year
flood flows. The undersized culvert at Colorado Boulevard
constricts the channel flow and contributes to the flooding

problem. In this portion of the Reach, flood damage potential

exists for damage to institutional and residential structures

and the road,,,ay at Colorado Boulevard would be overtopped.

Brantner Gulch from East Side of Colorado Boulevard to East
Side of Holly Street (Sheets 3-5)
Through this Reach, Brantner Gulch consists of a wide,
open earth channel on a moderate grade with gently sloping banks.
The bottom of the channel is densely covered with high weeds and
cattails. This Reach is predominantly undeveloped except for
residential development on the north and south sides of the
channel just east of Colorado Boulevard. A small wooden barn
is the only structure affected by the lOO-year flood in this Reach.
The present channel will contain the lOO-year storm runoff
within its banks without flooding any adjacent residential
structures. However, high velocities may result in erosion of
the channel and overbank areas.
The culvert under Holly Street does not have the capacity
to convey the lOO-year flood.

Brantner Gulch from East Side of Holly Street to East Side of
Quebec Street ( Sheets 5-7)
Through this Reach, Brantner Gulch is characterized by a
wide, open earth channel on a moderate grade with gently sloping