FLOOD03281

• County: Boulder
• Community: Boulder County
• Stream Name: Boulder Creek
• Basin: South Platte
• Title: Hydrology Addendum to FIS Boulder County and Incorporated Areas
• Date: 10/1/2000
• Prepared For: Boulder County
• Prepared By: Montgomery Watson
• Floodplain - Doc Type: Floodplain Report/Masterplan

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STUDY AREA DESCRIPTION

Community Description
Boulder County is located in north-central Colorado. The county is bordered by Larimer County
on the north, Weld and Adams county on the east, Jefferson and Gilpen County on the south and
Grand County on the west. The City of Boulder is the County Seat of Boulder County. The area
mapped in the FIRMs includes the entire county, including the incorporated communities of
Boulder, Jamestown, Lafayette, Longmont, Louisville, Lyons, Nederland and Superior.
Populations and growth rates for the communities are shown in Table I, The City of Broomfield
is partially located within Boulder County, However, because it is not completely contained
within the County, the City has its own PIS, The Towns of Ward and Aliens Parks are also
located in Boulder County. They are not covered by the PIS because there are no mapped
floodplains within the Towns' limits,

Table 1. Boulder County Incorporated Communities Population Data
1990 1999 Growth
Community Population Population Rate
City of Boulder 85,127 91,971 0.9%
Town of Jamestown 251 281 1.3%
City of Lafayette 14,708 22,034 4.6%
City of Longmont 51,976 66,303 2.7%
City of Louisville 12,363 18,558 4.6%
Town of Lyons 1,227 1,568 2.8%
Town of Nederland 1,099 1,270 1.6%
Town of Superior 255 8,811 48,2%
Boulder County 225,339 282,445 2.5%

Notes:
<'l The table only includes communities in the county that are included in
this designation,

Watershed Description
Boulder County is located on the eastern slope of the Continental Divide in the South Platte
River basin. The western portion of the county is mountainous, while the eastern portion of the
county is high plains. The two primary water courses in the county are St. Vrain Creek and
Boulder Creek, Boulder Creek is tributary to St. Vrain Creek in western Weld County, which is
then tributary to the South Platte River approximately 12 miles further down stream. Nearly all
streams within the County are tributary to either the St. Vrain or Boulder Creek, Elevations of
the watershed range from over 14,000 feet on Longs Peak to approximately 4900 feet as the St.
Vrain leaves the County east of Longmont. The western portion of the County is primarily
forested lands, with scattered developments primarily consisting of cabins and vacation homes.
The eastern portion of the County is urban development and agricultural lands_ The area has
seen significant development over the last 10 years.

There are several current USGS gaging stations within Boulder County located along the major
rivers and tributary streams, In addition, there are several sites that have collected data but are no
longer active. Several of these gaging stations have been used to estimate peak discharges in the
PIS. However, none of the gaging stations contain enough data to calculate peak discharges for
the approximate streams, which are the subject of the hydrology calculations in this report,

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