FLOOD09526

• Designation Number: 281
• County: Boulder
• Community: Boulder
• Stream Name: Boulder and Adjacent Boulder County Drainageways
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Boulder and Adjacent County Drainageways
• Date: 5/1/1987
• Designation Date: 10/1/1987
• Floodplain - Doc Type: Floodplain Report/Masterplan

flooding occurs south of Spruce Street on the east side of the creek. The
flooded area is caused by overland flows from the area north of Spruce Street,
between the creek and 4th Street, and the south eastward slope of the land away
from the channel. The shallow flooding zone extends eastward to 6th Street.
Street flooding down 3rd and 4th Streets diverts floodwaters from buildings
between Pearl Street and Canyon Boulevard. This shallow flooding area affects
more than 40 buildings.

T'IIOIllile Canyon Creek

Property damage due to flooding is fairly light in the upstream portion of
Twomile Canyon Creek between the upstream study limit and Kalmia Avenue. Within
this section, which crosses Linden Drive, eight residential buildings are flooded
which are within the floodplain. The floodplain is approximately 350 feet wide
at its widest pOint within this section.

Goose Creek

South of Kalmia to the stream's confluence with Goose Creek the amount of
property damage steadily increases. The floodplain ranges in width from 200 to
450 feet from Kalmia Street to Hawthorne Avenue. The floodplain extends
approximately 500 feet south of the Twomile Creek channel, to the south side of
Hawthorne Avenue 900 feet upstream from Broadway. Foothill Elementary School is
within the floodplain. The floodplain widens between Broadway and 19th Street.
Hawthorne Avenue is flooded along wi th severa 1 residentia 1 buil dings on 13th,
14th, and 15th Streets. As the creek follows Garland Avenue and extends to 19th
Street, further downstream the floodplain reaches Hawthorne Avenu~ to the north
and Forest Avenue to the south, flooding 33 residential buildings within the
area.

Flood damage along Goose Creek is generally heavy as the creek passes through
densely populated areas of the city. The floodplain near the upstream study
limit, which is located near 9th and Balsam, is about 400 feet wide. The
floodplain turns south on Broadway and then eastward on Alpine Avenue. Between
Broadway and 13th Street, the floodplain extends 500 feet to the south. South of
North Street, between 13th and 17th Streets, the flooding generally occurs
between Alpine Avenue and North Street. Several homes are flooded within this
area. Heavy property damages continue as the creek passes to the south of
Edgewood Drive. Between 19th and Folsom Streets, the floodplain extends
northward and intersects the floodplain from Twomile Canyon Creek. The
intersection of the two floodplains results in greater depths of flooding,
between 1.5 and 2.5 feet.

The most severe property damage along Twomile Creek occurs between 19th Street
and the creek's confluence with Goose Creek. On the north side of the stream,
the floodplain extends from the creeks channel at 19th Street to Glenwood Drive,
and to the intersection of Edgewood and Valmont Drives, near the streams
confluence. The floodplains extension to the south crosses Floral Avenue at 19th
Street, extends across Edgewood Drive 200 feet to the south at Nichol Street and
remains parallel to Edgewood Drive about 200 feet to the south. The damage
within this downstream portion of Twomile Creek is very heavy as buildings are
very dens-e. 19th Street, Floral Drive, Repplier Drive, Nichol Street, Loraine
Court and Edgewood Drive are all lined with residential buildings.

At Folsom Street the pattern of flooding is changed with the floodplain extending~
to the south of the Goose Creek channel. With the influence of Elmer's Twomile
Creek, the floodplain extends 1900 feet to the south, 200 feet past Spruce
Street. The floodplain borders the Union ;'acific Railroad Line to 30th Street.
At 30th Street, the floodplain extends 750 feet to the south, south of N. Boulder
Cree\(. East of 30th Street, the floodplain extends 2400 feet south from the
channel.

Downstream of Foothills Parkway the Goose Creek channel splits into two improved
grasslined channels. The channels converge at a sediment pond just upstream of
the confluence with Boulder Creek. The floodplain is confined to the improved
channels in this reach.

Elmer's Twomile Creek

Between the upstream study limit at Elmer's Twomile Creek and Glenwood Avenue,
extensive flood damage does not occur. Floodwaters back up behind Sherwood
Circle which results in floodwaters extending to Folsom Street and flow down the

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