FLOOD01898

• County: Larimer
• Community: Estes Park
• Stream Name: Big Thompson, Fall Rivers
• Title: Hydrology Report for Estes Park and Larimer County FIS
• Date: 2/1/1984
• Prepared For: FEMA
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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2.1

II. LITERATURE REVIEW

A summary and description of the available hydrologic analyses relevant

to this study is presented in this chapter.

2.1 Hydrology, Big Thompson River and Fall River

The Omaha District of the Army Corps of Engineers (COE) completed a

report titled "Hydrology, Big Thompson River and Fall River" in 1975

(Reference 1). The study developed peak flow values for 10-, 50-, 100- and

SOD-year recurrence intervals for locations on the Big Thompson and Fall

Rivers.

Nearly all of the annual peak discharges on the Big Thompson are due to

snowmelt. Peak flow values for the Big Thompson River at Lake Estes were

determined by developing discharge-probability relationships based on 44 years

of adjusted stream-gaging records available at this site.

Discharge-probability relationships for other sites on the Big Thompson

and at locations on the Fall River were developed using results from a

regional study. The regional study was based on records at 13 stream gages on

Colorado mountain streams with elevations greater than '7,400 feet above

m.s.l.

By examining the ratio of 500-year to 100-year peak flows for 32 other

Colorado mountain streams, it was concluded that the values for the SOD-year

events on the Big Thompson and Fall Rivers, as determined by extrapolating the

discharge-probability curve, were low. Therefore, new values for the SOO-year

events were estimated at twice the 100-year discharges.

The flow values obtained by this study are presented later, along with

values from other analyses, in Table 3.2. This allows comparison between the

values determined by each study.

2.2 Hydrology study, Estes Park Flood Insurance Study

Gingery Associates completed a hydrologic analysis for a flood insurance

study in the area in 1977 (Reference 2). Peak flow values for 10-, 50-, 100-

and SOO-year recurrence intervals were developed.