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<br />
<br />TABLE IV-ll
<br />
<br />The peak flow and volume of runoff resulting from a given storm event is highly dependent
<br />on three parameters: (1) intensity of rainfall, (2) the percentage imperviousness of the
<br />basin, and (3) the soil infiltration characteristics of the basin.
<br />
<br />FWOD INFWW TO STANDLEY LAKE AND GREAT WESTERN RESERVOIR
<br />ESTIMATED FROM CUHP AND SWMM
<br />
<br />
<br />The intensity of a given rainfall event varies throughout the event, The depth of rainfall for
<br />a given time increment can be tabulated to generate the distribution of rainfail for a given
<br />storm event. The distribution of rainfall for a short storm event has been thoroughly studied
<br />and defined for the Denver area. The rainfall distributions for the 2- and 6-hour storm
<br />events are presented in Tables IV-I and IV-2,
<br />
<br />"'.'...'~W~~~i
<br />
<br />100-year occurrence
<br />5O-year occurrence
<br />10-year occurrence
<br />
<br />5,700 cis
<br />5,100 ds
<br />
<br />
<br />The distribution of rainfall for longer storm events has not been well defined for the Denver
<br />area, The intensity of rainfall for a 2. or 6-hour design storm is higher than that for longer
<br />storm events because they are different types of storms (Tunnel, 1991). The short-term
<br />design storm is a thunderstorm with high intensity of rainfall. Long-term design storms are
<br />upslope storms with lower intensity.
<br />
<br />
<br />540 ac-ft
<br />
<br />WNG-TERM STORMS
<br />
<br />Long-term storm events (greater than 6 hours) are generally not analyzed in master drainage
<br />planning in the Denver area because experience has shown that short storm events produce
<br />more severe floods, Long-term storms are, however, analyzed in this study to assess their
<br />effect on the runoff volume at various points of interest on the plant site, In no case would
<br />a longer term storm event yield a greater peak flow than a shorter event. The long-term
<br />storm, 100-year point precipitation values for the Rocky Flats Plant site are listed in Table
<br />IV -12.
<br />
<br />The long-term Colorado storms of May 4-8, 1969 at Boulder; May 5-6, 1973 at Denver; and
<br />May 5-6, 1973 at Boulder, were analyzed for an indication of the distribution of rainfall
<br />within a long,term storm event, The total rainfall and peak one-hour intensity of the storms
<br />are listed in Table IV-13 (U.S. Department of Commerce, 1969, 1973).
<br />
<br />TABLE IV-13
<br />
<br />TABLE IV.U
<br />
<br />STORMS OF RECORD
<br />TOTAL RAINFALL AND ONE-HOUR PEAK INTENSIlY
<br />
<br />100-YEAR POINT PRECIPITATION (INCHES)
<br />FOR WNG.TERM STORMS
<br />
<br /> ~(~}i
<br />1-Day 4,1'
<br />2-Day 4.55'
<br />4-Day 5,0>
<br />7-Day 5,75'
<br />10- Day 6,0>
<br />
<br />
<br />
<br />",.'..,.,.~~IM...,.,.
<br />~"IJt""""')..,
<br />'.", '".,"", '..'otir i
<br />. - __. ,_ - _un ,-,.'.
<br />. ".."""',',,,,','.-,','."..
<br />
<br />'t;;Wi
<br />~&t:~.
<br />
<br />7,64
<br />3.50
<br />2,0
<br />356
<br />
<br />-:c':,.:'::,:::::'.',;":,,:,,':-,::-,,,':'"
<br />_:_'C'_,',._,""'_"_"_"_""':"':'_"
<br />c,':"',-'''-','-'-,-:-''-'':''-':'':'':':--''
<br />i.,...i......~,......,......'.'.
<br />, "bIliitUilJ
<br />
<br />4 days
<br />
<br />1 day
<br />
<br />1 day
<br />
<br />1 day
<br />
<br />5/4/69 - 5/8/69
<br />5/6/69'-1)
<br />5/5/73 - 5/6/73
<br />5/5/73 . 5/6/73
<br />
<br />Boulder
<br />Boulder
<br />Boulder
<br />
<br />,67
<br />,67
<br />,4
<br />.36
<br />
<br />Denver
<br />
<br />From Weather Bureau Technical Paper No, 40
<br />(V,S, Department of Commerce, 1965)
<br />
<br />2 From Weather Bureau Technical Paper No, 49
<br />(V,S. Department of Commerce, 1965)
<br />
<br />This is the largest one.day period during the 5/4 - 5/8/69 storm
<br />
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