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<br />major unforeseen changes, are reall~;ti: for future development. of <br /> <br />First Cr~~ek basin. At what time iTl tile [u1~ure such a level. of' <br /> <br /> <br />development will take place in FjrsL Creek basin is di.fficult to <br /> <br /> <br />predict at this time. <br /> <br />Uni~j-"'ograph" <br /> <br /> <br />Unit hydrographs were prepared for each of the 31. sub-basins <br /> <br /> <br />within the First Creek drainage and for the MonU)ello area in the lron- <br /> <br /> <br />dale Gulch basin. These hydrographs "ere prepared for both existing and <br /> <br /> <br />futu:ce development conditions. A Lola 1 (,f 70 un, t hydrographs "'ere pre- <br /> <br /> <br />pared. Then the design rainfall for 2-, 10-, awl lOO-year frequencies <br /> <br /> <br />were applied to the unit hydrographs to develop storm hydrographs. 11 <br /> <br />total of 210 storm hydrographs were developed. Losses were based on <br /> <br /> <br />evalllation of the soils survey for Adams all(1 Arapahoe Counties performed <br /> <br /> <br />by the U.S. Soil Conservation Service, n:'commencled ',alues in the Urban <br /> <br /> <br />Storfl Drainage Criteria Manual (USJJCM), >tudy of the natural depressed <br /> <br /> <br />areas, and existence of the East Branch of the Highline Canal and an old <br /> <br /> <br />cana:_ which traverses the First Creek basin. A~)propriate values for <br /> <br /> <br />losses as recommended in the Urban Strom Dr'ainagf~ Criteria Manual, were <br /> <br /> <br />Ilsed An average infiltration rate of or.e -half inch per hour, pervious <br /> <br /> <br />storage of O.lf inch, impervious storage (,f 0.1 inch and:) percent losses <br /> <br /> <br />were used in all cases. <br /> <br />S to rm -.!!L':lro gr a phs_ <br /> <br />The storm hydrographs for Lh. 25 sub-basins were added to- <br />geth{~r, taking into consideration the jiffpl~erlt l:ime and conveyance <br />charilcteristic:s of each reach into aCCOuD,t The storage aIId retarding <br />capacities of each structure on the water COUr-Sf were estimated, and the <br />resul ting combined hydrographs 11\-'ere devp 1 op(~d . Twenty-five "de sign <br />point.s", or critical places along the water courses were selected where <br />it would be useful to know the flow hydrcgl,olph f()r each design frequency. <br /> <br />1]....5 <br />