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<br />SECTi ON V I <br /> <br />DESIGN CRITEFiIA <br /> <br />The magn Itude of the size of the Big Dry cre",k drainage bas In, the <br />relatively undeveloped nature of the basin, the e>:istence of continued low <br />flows from Irrigation releases throughout '" substlOintIal portion of the year, <br />and the relative Infrequency of large magnitude storm discharges typical <br />of many streams, combine to make the design crltel'Ia for Big Dry Creek some- <br />what different than for basins that produce smaller runoff quantities In <br />areas already substantially urbanized. While basic hydrologic, hydraulic, <br />sociologic, economic, and other related principles are still viable, certain <br />subtle differences exist concerning constraints, as well as opportunities <br />that must be considered to achieve an effective preliminary design. With <br />the expanse of the Big Dry Creek flood plaIn, the approach to design must <br />consider multiple use, Including large scale use by people for recreatIon <br />and for pedestrian - bIke travel, and must consIder preservation of the <br />natural flora and fauna In certain areas. ThIs section lists and describes <br />the crIteria used in the preparation of this prelImInary desIgn, Including <br />those plans which were considered and dIscarded. <br /> <br />During Phase A of this study, it was determined that a "non-structural" <br />approach was the most desIrable manner by which t,o approach the Preliminary <br />Design. The partIcular alternate that was chosen Is a flood plain approach <br />with structural Improvements (channels, birdges etc.) limIted to those <br />areas where for fInancial and for other criteria it Is desirable to protect <br />appurtenant features and/or channelIze the flood waters. It Is Important <br />that the desIgn criterIa be well conceived so as to maximize the benefits <br />to be obtained and to Insure that the major drall1,age system will operate <br />as intended. <br /> <br />As Iterated In previous reports, the major drainage sy,;tem will operate <br />whether or not it is planned or designed, and whether or not urban development <br />Is wisely located In respect to It. In the first phase of this study, <br />much of the criteria for this report was established In that a concept was <br />determined and a design return frequency (100 year's) was chosen. <br /> <br />The criteria presented following constItute ," refInement in the criteria <br />used to determIne the concept and return frequency. The design criterIa <br />utIlIzed for thIs prelIminary design are thc)se contaIned In the Denver Re- <br />gional Council of Governments Urban Storm Dralnag'" Criteria Manual, Volumnes <br />One and Two. Specific planning and design criteria applicable to the Big <br />Dry Creek study are: <br /> <br />1. Natural Channels. Natural waterways will be used wherever feasible. <br /> <br />a. Channel and overbank capacity must bo!' adequate for design <br />runoff . <br /> <br />V I-I <br />