FLOOD03858

• Designation Number: 298
• County: Boulder
• Community: Unincorporated Boulder County
• Stream Name: St. Vrain Creek
• Basin: South Platte
• Title: Floodplain Information Report - St. Vrain Creek, Boulder County, Colorado
• Date: 8/1/1988
• Designation Date: 5/1/1989
• Floodplain - Doc Type: Floodplain Report/Masterplan

CHAPTER II

STUDY AREA DESCRH"I'TON

!,tudy Area Description

The St. Vrain Creek drainage basin tncorponltes a diverse topographic area

ext{~nd:i.ng from the Boulder-Weld County -: :;~ne west to the Contfnental

Divide, as illustrated on Figure 1.

Thi:~ reflects a change in elevatiDn

of over 9300 feet from the "estern basin :, J.!rits to the ]o"er limits of th,

study,.

The maj or tributaries of the_ St, IJ:rain Creek are tl,;e ;\!orth and

South St. Vrain Creeks, two steep gradieJ~r canyon streams, and Dry Creek

111 and Lower Lefthand Creek.

The North .:lrId South St. Vrain Creeks come

together at Lyons, Colorado, j.ncorporatillg 211 square miles of drainage

area to form what is known as St. Vrain Creek.,

D01mstream of Lyorts tne

St. Vrain Creek merges with Dry Creek :Ill ,:~nd Lower Lefthand Creek aJong

the

southern

city

limit s

of

Longmon t:,

Colora-no.,

accounting

for

approximately 351 square miles of drainagp arl2a at the lower limits of the

study.

A summary of the drainage area and r.:orresponding discharges at a

number of locatjons along the study basin <:::1:e listed in Tahle 1.,

In the mountainous areas a number of sma1 J lakes .and rl~ser.voirs exist,

mainly for agricul tural and domestic water :,l1pply. Buttonrock. Reservoir,

situated along the North St. Vrain Creek ;:Ippi.oxirnately six mi~.es upstream

of Lyons, Colorado, serves as a storapE~ facil.fty for tIle City of

Longmont's domestic water supply. Though thE! facility was not constructed

for flood control measures, the reservoj r :loes attenuate the peak fJ ows

generated along North St. Vrain Creek ,." they are routed through,

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