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FLOOD11770
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Last modified
1/26/2010 10:24:13 AM
Creation date
7/29/2008 10:56:13 AM
Metadata
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Template:
Floodplain Documents
County
Douglas
Community
Douglas County
Stream Name
Fourmile, Horse, West, Trout Creeks
Basin
South Platte
Title
Draft South Platte River Tributaries Hydrology Report
Date
5/11/2004
Prepared For
Douglas County
Prepared By
Moser and Associates
Floodplain - Doc Type
Floodplain Report/Masterplan
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<br />. <br /> <br />. <br /> <br />, <br /> <br />. <br /> <br />DRAINAGE CRITERIA MANUAL f'I. 1) <br /> <br />RAINFALL <br /> <br />three hours of the stonn as desaibed above. The difference between the 6-hour point precipitation from <br />Figures RA-1 through RA-12 and the 3-hour point precipitation is distributed evenly over the period of 185 <br />minutes to 360 minutes. <br /> <br />TABLE RA-2 <br /> <br />Design Storm Distributil:>ns of 1-Hour NOAA Atlas Depths <br /> <br />Tune PERCENT OF 1-HOUR NOAA Ra.INFAlLAnAS DEPl1-I <br />Minutes 2-Year 5-Year 1O-Year 25- and 50-Year 100- and SOO-Year <br />5 2.0 2.0 2.0 1.3 1.0 <br />10 4.0 3.7 3.7 3.5 3.0 <br />15 8.4 8.7 8.2 5.0 4.6 <br />20 16.0 15.3 15.0 8.0 8.0 <br />25 25.0 25.0 25.0 15.0 14.0 <br />30 14.0 13.0 12.0 25.0 25.0 <br />35 6.3 5.8 5.6 12.0 14.0 <br />40 5.0 4.4 4.3 8.0 8.0 <br />45 3.0 3.6 3.8 5.0 6.2 <br />50 3.0 3.6 3.2 5.0 5.0 <br />55 3.0 3.0 3.2 3.2 4.0 <br />60 3.0 3.0 3.2 3.2 4.0 <br />65 3.0 3.0 3.2 3.2 4.0 <br />70 2.0 3.0 3.2 2.4 2.0 <br />75 2.0 2.5 3.2 2.4 2.0 <br />80 2.0 2.2 2.5 1.8 1.2 <br />85 2.0 2.2 1.9 1.8 1.2 <br />90 2.0 2.2 1.9 1.4 1.2 <br />95 2.0 2.2 1.9 1.4 1.2 <br />100 2.0 1.5 1.9 1.4 1.2 <br />105 2.0 1.5 1.9 1.4 , 1.2 <br />110 2.0 1.5 1.9 1.4 1.2 <br />115 1.0 1.5 1.7 1.4 1.2 <br />120 1.0 1.3 1.3 1.4 1.2 <br />Totals 115.7 115.7 115.7 115.6 115.6 <br /> <br />3.2 Adiustment to Rainfall Distribution tclr Watershed Size <br /> <br />The NOAA Atlas provides guide6nes for adjusting the rainfall depths with increasing catchment area <br />Area-depth adjustments are given in the Atlas fnr durations of *-, 1-, 3-,6- and 24-hours. Raufe RA-14 <br />was based on a similar figure in the NOM Atel. The 15-minute curve was extrapolated by the District <br />from the infonnation shown for other storm durations on Fk:lure RA-14. The fast response times of <br />urbanized wateusheds and sharp rainstorm distribution gradients in the Denver area require adjustments <br />of rainfa" depths for stonn durations that are less than *-hour. <br /> <br />The area adjustment procedure can be tedious ;and time consuming; therefore, Table RA-3 is provided to <br />assist the engineer with the area-depth adjustment calculations. To adjust the design stonn distribution to <br />account for the averaging effects of larger wate.sheds, follow these three steps: <br /> <br />0612001 <br />Urban Drainage and Rood Control District <br /> <br />RA-4 <br />
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