FLOOD10344

• County: Boulder
• Community: Boulder
• Stream Name: South Boulder Creek
• Basin: South Platte
• Title: South Boulder Creek Correspondence
• Floodplain - Doc Type: Correspondence

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B. Flood History
Boulder is located at the base of the foothills where there is high potential for flash flood events that allows little
time for warning. A major flood event, particularly on Boulder Creek, would result in substantial property
damage and probable loss of life. Because the threat to life and property damage is so great, the need to manage
and regulate local floodplains is critical.

There are 13 major drainageways, or creeks, passing through Boulder that are ultimately tributary to Boulder
Creek at the eastern city limits. Approximately 15 percent of Boulder is located in the 100-year floodplain (more
than twice the national average of 7 percent), and this includes more than 4,000 structures (last reported to be
3,515 single-family to four-family residential structures and 646 other structures). Flooding from these various
creeks may be narrow and swift, as with Boulder Creek downtown and Bear Canyon Creek in Table Mesa, or
quite wide and highly dispersed, as recently identified for Fourmile Canyon Creek in North Boulder and South
Boulder Creek in the Keewaydin Meadows area.

The largest recorded flood in Boulder occurred over a four-day period along Boulder Creek from May 29 to
June 1, 1894. The estimated 100-year flood coursed through the city washing out the railroad, roads and
numerous structures. In July 1909, flooding along Two Mile Canyon Creek claimed two lives and hospitalized
two more. An estimated 40-year flood struck Boulder Creek again in 1914, with subsequent flooding in 1919
and in 1921.

Two Mile Canyon Creek flooded again in September 1933 demonstrating that floods can occur in late fall. The
largest flood of record for South Boulder Creek passed through Eldorado Springs and Marshall in 1938. The
Eldorado Springs Resort was significantly damaged washing away the dance hall and a number of cabins.
Boulder Creek also flooded at this time. In May 1969 an estimated 25-year flood damaged significant areas
along Boulder Creek, Bear Canyon Creek and South Boulder Creek.

Boulder has been spared the impact of devastating floods over the last 30 years. However, several events
estimated to be smaller than 20-year floods have occurred on the tributaries to Boulder Creek. Bear Canyon
Creek, Fourmile Canyon Creek, Goose Creek, Gregory Creek and Two Mile Canyon Creek have all experienced
over bank flooding.

Also in this region, floods that far exceeded the 100-year storm level occurred in the Big Thompson Canyon in
1976 and in Fort Collins in 1997. Flooding in the Big Thompson caused more than 140 fatalities and led to the
posting of highway signs that advise "climb to safety in times of flood." The Fort Collins flood caused the loss
of five lives in an area that was considered to be outside of the floodplain.

C. Floodplain Management History
The city of Boulder first adopted floodplain regulations in 1969 in response to Front Range flooding events.
Ordinance 3505, "Floodplain Regulations," was adopted August 17, 1969. The regulations defmed flood storage
and floodway areas within the floodplain and adopted a flood protection elevation for both residential and
commercial structures of two feet above the 100-year flood elevation. However, the floodway and flood storage
areas were not delineated at that time.

The city's first major drainageway master plans prepared by Wright-McLaughlin Engineers were adopted in
1969 and 1970. The master plans included Boulder Creek - 24th to 30th Streets, Boulder Creek Flood Slough,
North Boulder Tributaries and South Boulder Tributaries. These master plans were developed in conjunction
with.the then newly formed Urban Drainage and Flood Control District (UDFCD).

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