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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3.5 RainfaU <br /> <br />3.5.1 Criteria <br /> <br />The design rainfall events modelled for the study area were developed using criteria from <br />the Urban Storm Drainage Criteria Manual (USDCM) (UDFCD, 1969) and the National <br />Oceanic and Atmospheric Administration (NOAA) Atlas (NOAA, 1973). Tables 4-1 and <br />4-2 of the Rainfall Chapter of the USDCM stipulate criteria for general storm durations <br />and adjustments to rainfall based on watershed area. Table 3-2 indicates the area <br />adjustments, based on Tables 4-1 and 4-2 of the USDCM, used for this study. <br /> <br />I Table 3-2 I <br /> Summary of Area Adjustments <br /> Watershed Need for Locations Where Area Area <br /> Area Storm Area Adjustments Were Adjustment <br /> (sq.mi.) Duration Adjustment Applied Identifier <br /> 0-10 2-Hour no - all tributaries I <br /> - upstream portion of <br /> mainstem Coyote Run <br /> 10-20 3-Hour yes - middle portion of 2 <br /> mainstem Coyote Run <br /> (3.1 to 9.8 miles <br /> upstream of north <br /> study limit) <br /> 20-30 6-Hour yes - downstream 3.1 miles 3 <br /> of mainstem Coyote <br /> Run <br /> 50-75 6-Hour yes - mainstem Box Elder 4 <br /> Creek in study area <br /> and upstream of study <br /> area <br /> <br />3.5.2 Rainfall Depths <br /> <br />Rainfall depths for 1-, 3-, and 6-hour durations were determined from the NOAA Atlas <br />(NOAA, 1973). One-hour rainfall depths were used to produce 2-hour durations storms <br />according to criteria shown in Table 3-1 of the Rainfall chapter of the USDCM <br />(UDFCD, 1969). The I-hour depths were estimated for the 2-year and lOO-year storm <br />events using the equation provided in Table II of the NOAA Atlas for Region I (South <br /> <br />DENlOOI5186.WPS <br /> <br />3-3 <br />