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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"Whe'Y'e a late'Y' floodflow-f'Y'equeney analysis p'Y'ovides diseha'Y'ges that
diffe'Y' ['Y'om those established p'Y'eviously in studies on the same st'Y'eam, the
latest diseha'Y'ges shall e adopted if the p'Y'eviously established diseha'Y'ges do
not fall within the 95 and 5 pe'Y'eent eonfidenee limits (90 pe'Y'eent eonfidenee
inte'Y'valJ of the most 'Y'eeent estimates; the p'Y'eviously established diseha'Y'ges
shall be adopted if they fall within the 15 and 25 pe'Y'eent eonfidenee limits
(50 pe'Y'eent eonfidenee inte'Y'vaZJ of the most 'Y'eeent estimates". (Reference 7).

The Gingery estimates are the most recently published flows used for

flood studies and will be used for comparison. The COE estimates are provided

as an additional reference. The Gingery estimates are all within the 90 per-

cent confidence interval of the present calculations. The Gingery estimates

not within the 50 percent confidence interval are the 10-year flow on the Big

Thompson and the 100- and SOO-year flows on Fall River.

Based on the consistency of the flow estimates between the present study

and the Gingery study, the recommended flows to be used for the current flood

study are Gingery flows for the Big Thompson River and Black Canyon Creek.

Even though the 10-year flow for the Big Thompson does not fit the required

confidence intervals, the Gingery analysis is based on a sufficient gage

record.

Flows on Fall River should be based on the more recent calculations.

This will make them more consistent with peak flows on the Big Thompson River
and Black Canyqn Creek.