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<br />SECT ION III <br /> <br />A. HYDROLOGY <br /> <br />The Colorado Unit Hyd]~ograph Procedure as out:lined in the Denver Regional <br />Council of Government I s Urban Storm Drainage Cri teria Hanual "\"35 used in <br />the hydrologic evaluation. The tabulation of the parameters used arE given <br />as follows: <br /> <br />TABLE III-I <br />HYDROLOGIC PARA.l'IETERS <br /> <br />Area (s<[. mile) <br />Time coefficient (CT) <br />Peak coefficient (Cp) <br />Length (mile) <br />Length CA (mile) <br />Unit Tine (min.) <br />PerviouH (I~) <br />Storm Duration (hr.) <br />Perviouf: storage (in.) <br />Infiltration (in./hr. @ <br />Losses (%) <br />Calculated <br />Impervious <br /> <br />1 hour) <br /> <br />1.13 <br />.34 <br />.54 <br />1.82 <br />.9 <br />10 <br />.75 <br />2 <br />.4 <br />.5 <br />.1 <br />2 <br />.1 <br /> <br />time increment <br />storage (in.) <br /> <br />(min.) <br /> <br />The 2, 5, 10 and lOa-year storm hydrographs were computed anc' the tabll- <br />lation of each given i.n Tables 111-3 thru 6. <br /> <br />The storm frequency if: defined as the time interval within which a storm <br />will be equalled or e:>:ceeded once. Thus, a 10--year storm would theoreti- <br />cally occur once in lCl years. <br /> <br />A single storm hydrograph for each freqllEncy storm "as prepared for the <br />725 acre basin. <br /> <br />The rainfall data as presented in the Drainage 11anual w,>re used to simulate <br />the particular storm frequency studied. The Intensity-Duration curves <br />given in Figure 111-1 were produced from the Rainfall"'Duration-Freqllency <br />curves shown on FigUrE' 111-2. These curves can be utilized to determine <br />the runoff rate from "pecific sub-basin areas of less than 200 acres. <br /> <br />Tile technical aspects of the CUHP Hethocl are not contained in this report <br />and if that informatic'n is desired, the prain!".8e Hanll~! should be conslllted. <br /> <br />B. GEOLOGY <br /> <br />The basin has a wide range of geologic formations with respect to infiltra- <br />tion rates. Porous Pinery Creek alluvium and sandy to elayey alluvium is <br />p:cesent in most of thE basin. <br /> <br />South Table Mountain is principally a layer system of basalt on top, with <br />side slopes of the Derver formation claystone that lead into the Piney <br />alluvium. <br /> <br />8 <br />