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<br />COM
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<br />
<br />. CAMP DRESSER & McKEE INC,
<br />
<br />Writer's Tower, Suite 1100
<br />1660 South AlbIon Street, Denver, Colorado 80222
<br />303 758-4351
<br />
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<br />d~. 251981'"
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<br />environmental engineers. scientisrs.
<br />planners. & management consultants
<br />
<br />March 24, 1981
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<br />
<br />CDN has completed the review of the Army Corp of Engineers hydrologic
<br />analysis of ~heygnne',B~and cam~ creeks in Colorado Springs, Colorado,
<br />[This hydrologiCliTfOrmatton is ~UIII <idzed in the 1976 COE Report
<br />on Hydrologic Investigations for Flood Insurance Studies in El Paso
<br />County and Colorado Springs, Colorado.
<br />
<br />"~ J.;A
<br />NIQ , (!\At.
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<br />
<br />Dr. John Liou, P,E,
<br />FEMA
<br />Denver Federal Center
<br />Building 710
<br />Lakewood, CO 80225
<br />
<br />Dear John:
<br />
<br />The methodology used to compute the peak flow rates for the 10-, 50-,
<br />100- and SOD-year frequencies was a unit hydrograph procedure in
<br />urban sub-basins of each major basin combined with the use of TM-1
<br />in the undeveloped portions of each basin, The details of this pro-
<br />cedure is summarized in CDWs Hydrologic Review for Flood Insurance
<br />Studies submitted to FEHA in December of 1980,
<br />
<br />The urbanized areas in the lower portions of Cheyenne, Bear and Camp
<br />creeks were field checked by CDN to establish whether or not develop-
<br />ment had changed the overall basin characteristics from those used
<br />by the CaE in their 1976 Report, All of these basins have shown
<br />little or no growth in sub-basins where a unit hydrograph procedure
<br />was applied, and therefore COM did not alter any of the peak flow
<br />rates in such basins, Furthermore, CDM checked the COE assumption
<br />that the areas above 9000 feet in elevation be excluded from the
<br />TM-1 calculation for the undeveloped portions of each creek. According
<br />to the procedures outlined in m-1 CDM found that the lower "Plains"
<br />Region regression curves should be used in computing the peak flow
<br />rates for the undeveloped portions of each basin, as the COE assumed
<br />in their 1976 report. All of the hydrologic parameters used by the
<br />,,,CaE for calculating peak flow rates using HI-I were checked and found
<br />~\,O" to be accurately estimated,
<br />'"
<br />n~v' ~CDM recommends that the flow rates contained in the 1976 CDE report
<br />, '~ \ be adopted for use in the current Flood Insurance Study for Colorado
<br />fJ C",/ "",,J') Springs and El Paso County, These flows are summarized in the attached
<br />.Y' I Table L These flo~1 rates \'iill be used in the hydraul ic analyses of
<br />-;v . "i, ' ~Cheyenne, Bear and Camp creeks.
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