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<br />" <br /> <br />.F <br />A <br />/.'& <br />A~ <br /> <br />.- <br />Frasier & Gingery, Inc. <br /> <br />.- <br /> <br />'.- <br /> <br />'~... -:tl\,ir:Fn~--: <br /> <br />2840 SOUTH VALLEJO STREET <br />ENGLEWOOO, COLORAOO 80110 <br />TELEPHONE JOJ 751-4860 <br /> <br />MEMORANDUM <br /> <br />TO: Mr. Bill DeGroot <br />Urban Drainage & Flood Control District <br /> <br />SUBJECT: Six Streams Group I Hydrology, Second Creek & Third Creek <br />Frasier & Gingery Job No. 1041.030 & 1041.040 <br /> <br />DATE: <br /> <br />April 1, 1975 <br /> <br />BY: <br /> <br />Charles G. Swanson <br /> <br />As a first step in delinating flood plains on Second and Third <br />Creeks, it was necessary to conduct a detailed hydrologic in- <br />vestigation. This investigation was carried out for the 100- <br />year storm frequency. In the hydrologic evaluation, projected <br />land use maps were used as a basis for determining future basin <br />conditions. Flood hydrographs were computed to define the rate <br />of runoff at selected design points as well as the volume of <br />runoff characteristic of the storm frequency and the type of <br />development within the basin. The method used to compute the <br />flood hydrographs was the Colorado Urban Hydrograph Procedure. <br /> <br />SECTION A - DESIGN POINTS <br /> <br />To facilitate the evaluation of intermediate points along both <br />creeks, four design points were selected within each study area <br />to permit a detalied investigation of the total drainage basin. <br />Exhibit 1, Basin Map, shows the location of the four design <br />points and six corresponding sub-basins for Second Creek and <br />the four design points and five corresponding sub-basins for <br />Third Creek. The sub-basin boundaries have been determined <br />primarily on the basis of natural topography, field inspection, <br />and street, water & irrigation ditch locations. In a few loca- <br />tions such as at major irrigation structures the sub-basin <br />boundary at the design point is not completely representative <br />of the surface runoff pattern for both the major and minor <br />storm events. On Second Creek, all low-flow is intercepted <br />by the O'Brian Canal, then any flow generated below the O'Brian <br />Canal is again intercepted by the Fulton Ditch. The two ditches <br />listed above also affect Third Creek in the same way. In this <br />study, only the major 100-year flow was considered and for this <br />reason, the irrigation ditches were not assumed to accept any <br />flow from Second and Third Creeks. <br /> <br />(,. i. I..~,~.l!. t.(. <br /> <br />lAp..,;O ~U~ ....flING <br /> <br />STORM DRAINAGE I STRUCTURAL <br /> <br />TRANSPORTATION I WATER & SANITA.TION <br />