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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 INTENSI1Y <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 />. - __. ,- - ----- ,-,.'. <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 />(U.S. Department of Commerce, 1965) <br /> <br />2 From Weather Bureau Technical Paper No. 49 <br />(U.S. Department of Commerce, 1965) <br /> <br />This is the largest one-day period during the 5/4 - 5/8/69 storm <br />