WSP11466

• File Number: 8441.400
• Description: Colorado Big Thompson Project - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 12/1/1976
• Author: Gingery Assoc.
• Title: Special Flood Plain Information Report - Big Thompson River and Tributaries - Larimer County CO - Volume 1
• Water Supply Pro - Doc Type: Report/Study

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A tabulation of the flood discharges used in this study
for all the study areas is provided in Tables 6-12 included in
the APPENDIX.

A detailed description and summary of the hydrologic
analyses and computations is available at the offices of the
Colorado Water Conservation Board.

HydraUlic An'alysis

A hydraulic analysis was completed to determine the flood
elevation for the 10-, 50-, 100- and SOD-year flood events on
each of the streams in the study area. This analysis was
completed using the Corps of Engineer's, HEC-2 Water Surface
Profiles Computer Program (Ref. 8). Cross-sections of the river
bottom for use in the hydraulic study were provided by Kucera
& Associates, Photogrammetric ConSUltants, in the form of
digitized cross-sections and aerial, topographic maps. The
cross-sections and maps are specified to be representative of
the study area as of September 5, 1976.

Channel and flood plain ;l:"oughness coefficients, (Manning's
"nil values) used in the analysis were selected to be representative
of typical flood plain conditions. The coefficients were
,
established from information gathered from field inspection,
consultation with other agencies includingth.'tt~tJ.i-Cdli:l1tad6
State University and the Colorado Highway Depa-t-6nent a's well
as from estimates based on hydraulic relationShips and hydraulic
publications (Ref. 9, 10). The roughness factors used in the
analyses are summarized in Table 5.

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