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<br />Table 4. Values of standard storm parameters for various ratios of I-hour to corresponding 24-hour rainfall <br />depth computed from the standard intensity-duration relationships in Table 3 and Figure 3. <br /> <br />Rainstorm Ratio# (%) <br />Parameter <br /> 10 15 20 30 40 60 <br />a) 4,58 6.57 8.91 14.35 22.57 40,01 <br />b] -2.84 -0.80 1.04 4.12 7.48 11.52 <br />c1 0.309 0.420 0.507 0.632 0.738 0.872 <br />a1 8.74 5.86 5.11 4,75 <br />bCj <br />1 <br />-.:J.. (~r 2.72' 4.95' <br />bC] I +C] <br />1 <br />a1 (.1 . Cl~1 +c1 1.43' 2.02' <br />bC' I +c) <br />, <br />14 8,22' 2.77' <br />I.c] <br />* For negative b only. <br />#Ratio of 1.hour to corresponding 24-hour rainfall depth. <br /> <br />T,td <br />r av <br /> <br />al <br /> <br />. . . . . . . .. . . . . . . . . (35) <br />cl <br />(td + bl) <br /> <br />rT,1 <br />av <br /> <br />in which r~~td is the T-year td-hour (or minute) <br />average rainfall intensity; r T,~ is the T.year l.hour <br />average rainfall intensity; ana ai' b1, and cI are the <br />standard storm parameters describing the ratios of <br />various-duration intensities to l.hour intensity for the <br />same frequency, as shown in Appendix C. If Eqs. 6 <br />and 35 are identical, comparing the parameters of <br />both equations yields <br /> <br />a ~ alrI,1 , . . . . . . . . . . . . . . . . . . . . .. . . . (36) <br />av <br /> <br />b ~ bl . . . .. . . " . , . . . . . . . . . . , . . . . . . . (37) <br /> <br />C ~ cl ........ . . . . . , . . . . . . . . . . . . . . . (38) <br /> <br />whence <br /> <br />T,td <br />r av <br /> <br />a rT, I <br />I av . . . . . . . . . . . . . . . . . . . (39) <br />(td + b)c <br /> <br />Given or knowing the ratio of I-hour to <br />corresponding 24-hour rainfall depth for any <br />frequency, the values of ai' bl (~b), and c 1 (~c) can <br />readily be determined from Fig. 4. Substituting the <br />ai' b, and c values so estimated and the known I-year <br /> <br />18 <br />