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<br />Y2 = 0.218 + 0.709[X1(X/X2)] <br /> <br />where , XI is the 2-year 6-hour depth. X2 is the 2-year 24-hour depth. Rainfall depths at <br />intermediate return periods are derived by interpolating between the 2- and IOO-year I-hour <br />depths according to Figure 2. <br /> <br />w <br />~ <br />= <br />u <br />c <br /> <br /> -. f <br />'" , <br /> - I - <br />- - - ----- ~- -----T-- <br />.,. <br /> - - <br /> i -- --~~- ~-- <br />'" -~- ---~. -~ <br /> - , ;:,11 <br /> : i,~~' <br /> -i----- '.~ <br />N i "',0:;' <br /> - - 1.7';: - <br /> ;,~ I <br />- <br /> - - <br />0 <br />2 5 10 25 50 100 <br /> <br />dIe <br />/ <br /> <br />.... <br />.:.-64~"l <br /> <br />= <br />a. <br />. <br />o <br />c <br />~ <br />:l <br />'Q. <br />'u <br />. <br />.. <br /> <br />;,);.vI... <br /> <br />Return Period in Years, Partial.Duration Series <br /> <br />Figure 2 - Precipitation depths for intennediate return periods. (Source: Miller, 1973). <br /> <br />This formulation gives only the storm depth. For the models to process the storm information, <br />the depth must be temporally distributed. Livingston and Minges (1987) studied 236 storms <br />during the convection season (May through mid-October) in the plains region of Colorado. <br />Using 5-minute intervals, the average storm was distributed as illustrated in Figure 3. The <br />design rainfall intensity is assumed to be a linear function of this temporal distribution. <br /> <br /> 0.25 <br />= <br />lS. 0.20 <br />~ <br />C <br />E <br />s <br />.. <br />a 0.15 <br />0 <br />.... <br />e; <br />c <br />:8 0.10 <br />u <br />e <br />... <br /> 0.05 <br /> 0.00 <br /> <br />0.30 -------- <br /> <br />-- - ------- - ------ --- - ----- <br />- - - - ----- <br /> - - <br /> I <br /> I I I <br /> <br />Figure 3 - Average distribution of convective rainfall events in the plains of Colorado in 5-minute intervals <br />(Livingston and Minges, 1987). <br /> <br />5 <br /> <br />/" <br />