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<br />. <br /> <br /> <br />. <br /> <br />. <br /> <br />CHAPTER 5 <br />HYDROLOGY <br />SECTION 2.0 <br />RUNOFF <br /> <br />COLORADO STATEWIDE <br />DRAINAGE AND FLOODPLAIN MANAGEMENT CRITERIA MANUAL <br /> <br />CHAPTER 5 <br />HYDROLOGY <br /> <br />SECTION 2.0 <br />RUNOFF <br /> <br />2.1 INTRODUCTION <br /> <br />This section presents the criteria and methodologies <br />for determining the storm runoff peaks and volumes <br />to be used in the preparation of storm drainage <br />studies, plans, and facilities design in the Slale of <br />Colorado. The practical analysis guidelines for the <br />three deterministic hydrologic methods (Rational <br />Method, HEC-1 (or HEC-HMS), and CUHP) are <br />provided in this section. For more in-depth <br />discussions of the modeling methods, theories, and <br />procedures, the users of this manual are referred to <br />the following program users manuals. <br /> <br />The practical analysis <br />guidelines for the <br />three deterministic <br />hydrologic methods: <br />Rational Method, <br />HEC-1 or HEC-HMS, <br />and CUHP are <br />provided in this <br />section. <br /> <br />· US Army Corps of Engineers, Hydrologic Engineering Center, HEC-1, Flood <br />Hydrograph Package, User's Manual, June 1998 <br /> <br />· Urban Drainage and Flood Control District (UDFCD), Users Manual, <br />Colorado Urban Hydrograph Procedure Computer Program - CUHP, PC <br />Version, 1995 <br /> <br />2.2 <br /> <br />RATIONAL METHOD <br /> <br />The Rational Method has been widely used for the sizing <br />of storm sewers and for determining rainfall-runoff design <br />values for small drainage basins with an area less than <br />160 acres. Even though this method has frequently come <br />under academic criticism for its simplicity, no other <br />practical drainage design method has evolved to such a <br />level of general acceptance by practicing engineers. The <br />Rational Formula method, when properly understood and <br />applied, can produce satisfactory results for determining <br />peak discharge estimates. The limit of application of the <br />Rational Method is approximately 160 acres. The <br />assumptions used in the Rational Method become less <br />valid for larger areas. For drainage basins equal to or <br />larger than 160 acres, more rigorous rainfall-runoff <br />analysis should be performed utilizing HEC-1, HEC-HMS, <br />or CUHP program. <br /> <br />AUGUST 2002 <br /> <br />RUNOFF <br /> <br />The Rational <br />Method has been <br />widely used for the <br />sizing of storm <br />sewers and for <br />determining <br />rainfall-runoff <br />design values for <br />small drainage <br />basins with an <br />area less than 160 <br />acres. <br /> <br />CH5-203 <br />