FLOOD01357

• Designation Number: 107
• County: Jefferson
• Community: Unincorporated Jefferson County
• Stream Name: Green Mountain Area
• Title: FHAD - Green Mountain Area
• Date: 4/1/1978
• Designation Date: 7/11/1978
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The flood hazards in the reach consist of erosion, debris removal

Due to the limiting capacity of the 6th Avenue culvert, the flood
plain below 6th Avenue is generally contained within the channel area.
Some additional flooding occurs from the locally generated storm runoff.
The flood peaks that split at 6th Avenue follow along the south side of
6th Avenue and combine with the flows in Drainageway G. The flood plain,
with 100 year frequency culvert improvements at 6th Avenue, is also shown
on the drawing to illustrate the effects of upstream improvements. Large
areas of sheet flow exist due to inadequate culverts and poorly defined
channel s.

and cleaning, and a low life hazard due to the high velocity steep channel,
6. Station 75+00 to 35+00, Upstream Study Limits to 6th Avenue
\Sheets 40 & 41t
The channel in this reach (designated Drainageway G-2) varies
from street flow within the residential area to a broad shallow swale
in the upper reaches. The channel has an average slope of 5%, The flood
plain varies from shallow overland flow to high velocity street flow.
The flood plain includes a broad expanse of shallow flooding within the
development where the flow does not follow the street alignments. The culvert

flooding would result downstream of 6th Avenue.

The flood hazards in the reach consist of erosion, debris removal
and cleanup, interrupted traffic and services, structural and content damage
to the residences, and a low to moderate life hazard due to the large
inundated residential area.

at 6th Avenue, which has very limited capacity, causes flow splitting toward

the east, If culvert improvements are made at 6th Avenue, additional

The flood hazards consist of erosion, debris removal and cleaning,
content and structural damage to the residences, content and structural
damage in the industrial area, interrupted traffic and services, and a

low to moderate life hazard due to the shallow high velocity flow.

7. Station 28+00 to 0+00, 6th Avenue to Drina
Sheet 42

8. 6th Avenue to 1-70, (Sheets 43, 44, 44A & 44B)
Due to the extensive flooding that occurs in the reach as a
result of the flow splitting at the various 6th Avenue culverts, two
general plan maps showing the flooding were prepared. The flow split flood
plain, which originates in Drainageway G-2 (Sheet 41), follows along the
south side of 6th Avenue, combines with the locally generated runoff at
Indiana Street, and flows north across the residential area. Due to the
lack of a definite channel, the flood plain covers a broad area with
shallow overland flow. The shallow flooding continues northeasterly across
Colfax Avenue along the east side of 1-70, flooding the commercial area and
mobile home park.

The channel in this reach varies from a well defined V-shaped

section in the upper and lower portions of the reach to a poorly defined

overland flow area in the middle portions of the reach. The channel

traverses through a low density residential area and has an average slope

of about 3.2%. Drainageway G-2 is tributary to Drainageway G just upstream

of Colfax Avenue (Station 26+70).

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