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<br />use in the Denver Metropolitan area. The Colorado <br />Urban Hydrograph ProcedurE: makes use of a 2-hour design <br />storm ~hat has been defined for 10 minute intervals <br />using ratios of the 1-hour rainfall amount for the <br />desired return period. <br /> <br />There are a multitude of design storm methodologies <br />that helve been developed by many different; investiga- <br />tors. I will focus on the Colorado Urban Hydrograph <br />Procedure (COOP) and the SCS unit Hydrograph Procedure. <br />Th,~ CUHP and SCS Design storm :Methodologies both make <br />us,~ of a unit hydrograph appro;~ch. l~ unit; hydrograph <br />is the hydrograph resulting from one inch of runoff <br />occurring uniformly over the watershed and over a <br />specified time interval known as the unit hydrograph <br />duration. The SCS unit hydrog-raph is presented as a <br />series of ratios to time to peak and peak discharge. <br />Use of the specified dimensionless ratios insures that <br />the developed unit hydrograph will have a volume equal <br />to one inch of runoff over the watershed. The CUHP <br />procedure for developing the unit hydrograph is a <br />variation on the Snyder 11et.hod unit hydrograph initial- <br />ly developed by the U. s. ),rmy Corps of Engi.neers. The <br />calculation of the time to pea}:, the time base of the <br />un! t hydrograph, and t:he peak discharge of t.he unit <br />hydrograph i.s accomplished using empirical equations <br />that have been developed by the Urban Drainage and <br />Flc>od Control District (UDFCD) by calibration to local <br />dat;a. The COOP methodology has gained widE, acceptance <br />in the Denver Metropolitan area. I would recommend <br />caution in the use of this method for other urban <br />are,as. <br /> <br />~ <br />The next step in the application of a design storm <br /> <br />methodology is 1:he calculation of :r:unoff sometimes <br /> <br />9 <br />