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<br />f:tandard project cloudburst storm amounts (3 hour duratioln) equivalent
<br />to 40 percent of PMP were adopted for F()rtificatioll Creek, Pil1'~ Ridge
<br />Gulch, Cedar Mountain Gulch, and the Other small tributaries around
<br />Crai~;. PMP amounts were determined fro~' reference 5. A comp,n:ison of
<br />point: SPS at Craig with a precipitation fre'juency analysis of historical
<br />3-hou,r May to October amounts at Craig (chart 7) indicates SP:; amounts
<br />are r'easonable.
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<br />Three cloudburst storm centerings WE!re used. One storm was centered
<br />over subarea 1 to determine peak flows foOl' Fortification Creek. A second
<br />storn, was centered over subareas 2-5 to detE!rmine peak flows JE"r these areas.
<br />A third storm was centered over subareae. 6-10 to dE!termine peak flows for
<br />these: areas. Subarea 1 is quite large in comparison to the s:[.~e of the
<br />cloudburst storm. Accordingly, flood computations for this al:ea were made
<br />assuming only a portion of the basin was contributJlng. Contr:Lbuting areas
<br />are listed on table 2.
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<br />Cloudburst storm amounts for the mor,~ h'equent events wer" based
<br />on ratios to the S1'S determined from. Chart 7. NOAA Atlas amonnts were
<br />not used since they are based on an analys1.e, of annual maximun, data
<br />whereas cloudbursts usually occur in thE! summertimE!. Hourly distribution
<br />of storm amounts were patterned after th,~ PMP distr'ibution.
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<br />c. Unit hydro!;raphs and loss rates .- S1.nce thE,re is a lad, of
<br />reproducible rainfloods in the Yampa RiV',~r basin unit hydrogr,lphs and
<br />loss rates were estimated. Unit hydrographs' were prepared for the
<br />subareas shown on Charts 1 and 2. Unit hydrographs: were computed using
<br />the modified Los Angeles District summat:[on hydrograph (S-curvE!)
<br />pro(:edure as outlined in Reference 6. Unit hydrograph chara'~t"ristics
<br />are tabulated on Table 2. The general m,<1untain and Farmington,. New
<br />Mexico S-curves were used and are shown on Chart 11. The adopted
<br />S-curves and ii values are consistent with those used for sim:l.lJ.ar
<br />are<lS in the FPI studies for Steamboat Springs, and Rangely, Colorado
<br />and Rock Springs, Wyoming.
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<br />Losses were computed using the initi..l a.nd COIlstant loss <:oncept.
<br />Adopted losses are tabulated below.
<br />
<br />lIasin
<br />
<br />Initial
<br />Loss (in)
<br />
<br />CClf.Lstant
<br />Lc~'s (in/hr)
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<br />Fort:iEication Creek
<br />PinE' .and Cedar ~ltn. Gulches and other
<br />small streams around Cr&ig
<br />Yampa River above Fortification Cr.
<br />
<br />0.75
<br />
<br />'115
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<br />0.5
<br />Varies
<br />0.4-1.6
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<br />The losses used for the small streams: around Craig are sim.!.liar to
<br />those used for similiar areas at Rangely. H:l.gher initial losses were used
<br />for F,)rtification Creek and the other highler elevation subar"as in the
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