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<br />PRECiPITATION (inches]
<br />
<br />-l
<br />-+~
<br />I '-.:-j
<br />
<br />Detailed computations for various floods on the Sand Creek water-
<br />are presented in the Technical Addendum (Leaf, 1933).
<br />Design hydrographs for Sand Creek at Pioneer Park for 5,10,25,50,
<br />lOO, and 500-yearfloods aresl10wn in Figure 10. Table 1 sUlll11arizes
<br />design peak flows and runoff volumes generated from a 3-hour storm.
<br />Regional Design Curves
<br />
<br />S.3.
<br />sheds
<br />
<br />Undeveloped Areas
<br />From the analysis aT peaK flews for the 5 through SOO-year floods
<br />on Sand CreeK, 5-1, 5-2, and 5-3, a series of relationships were developed
<br />which relate flood peaKs for a given recurrence interval to basin drainage
<br />area. These relationships, plotted in Figurel1,wereused to estimate
<br />flood peaKs on the undeveloped portions of watersheds comprising the
<br />remainder of the drainage baSin tributary to the Pioneer Ditch (Figure 8).
<br />As seen in Figure 8 the remaining drainage uea lies generally below
<br />Sterling NO.1 Ditch between Riverside Cemetary and the east-west segment
<br />of the Pioneer Ditch.
<br />
<br />Developed Areas
<br />PeaK Flows in thePioneerOitchgeneratedbythedevelopedportlon of
<br />the drainage basin were estimated using the.'Rational equation" written
<br />as:
<br />
<br />-~:~
<br />
<br />Q "'CIA
<br />where Q '" the peak flow in c.f.s.,
<br />C : the runoff coefficient,
<br />I . the rainfall intensity corresponding to the time of
<br />concent:-ationof the watershed in in./hr., and
<br />A '" the watershed area in acres.
<br />Runoff coefficients were determined from an anlysis of impervious areas
<br />within the city limits of Sterling. Average impervious area varies from
<br />24 to 80 ~"rc"nt in " se<,;tors of the city. As.url~<.i runuff <,;ol!f1ciel,t,
<br />for each sector are as follows:
<br />
<br />-0
<br />
<br />LJ
<br />. I
<br />I . ,
<br />,
<br />I
<br />
<br />Percent
<br />Impervious
<br />14
<br />30
<br />42
<br />80
<br />
<br />Runoff
<br />Coefficient
<br />0.40
<br />0.45
<br />0.55
<br />0.92
<br />
<br />"
<br />
<br />Figure 9:
<br />PRECIPITATION. FREOUENCY CURVES for SAND CREEK
<br />WATERSHEDS near STERliNG, COLORADO
<br />
<br />:5
<br />
<br />16
<br />
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