FLOOD05356

• County: Jefferson
• Community: Jefferson County
• Stream Name: Cub Creek
• Basin: South Platte
• Title: Request for Conditional Letter of Map Revision for Cub Creek
• Date: 6/1/1992
• Prepared For: State of Colorado
• Prepared By: Greenhorne & O'Mara, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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III.

elevations for lIpper Bear Creek (Figure C). This demonstrates that our HEC-2

model is working properly. The complete 'calibration' computer run and flood

profiles (FigurE' D) is provided in the Appendix.

Since the time the original hydraulics were completed, new, more detailed

mapping was deVIl loped for the study reach. This mapping is at a scale of l'

40' with a 1 foot contour interval. The new mapping indicates that

topography changes have occurred along the creek area. Therefore, a new

'existing' hydnulic analysis is necessary to define the floodplain as it

exists in its present condition. A HEC-2 analysis was completed using the

new topography in the study reach area. The 100-year and 500-year floodplain

are shown for the existing condition on Map Sheet 1 (in plan pocket). The

HEC-Z data is included in the Appendix.

A HEC-Z analysis was then completed using the proposed plan for construction

of the new library. Generally this plan includes removal of the brick and

stucco building (south end of the site) and construction of a new building

along the east end of the property. Regrading of the area is proposed for the

parking areas adj acent to the new buildings. The new 100-year and SOD-year

floodplains are shown for the proposed improvements on Map Sheet Z (in plan

pocket). The HEC-Z runs are included in the Appendix.

STUDY LIMITS

The downstream limits of the proposed improvements are approximately 1,000

feet upstream of the confluence of Cub Creek and Little Cub Creek. The

hydraulic calculations start just downstream of this location at FIS Section

Q which is shown on the original FIS profiles (Figure E).

The upstream limits of the proposed improvements extend approximately 1,200

feet south. Th,~ hydraulic calculations are extended to HEC-Z cross-section

118 which approximately equals FIS Section V (from the FIS profile). The new

flood profiles were drawn to show a tie into the existing FIS Section X

(Figure F).

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