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<br /><e <br /> <br />'. <br />.:'!-,; <br />.. <br /> <br /> <br />where "Q" is peak discharge in cubic feet per second (cfs), "C. is a coeffi- <br /> <br />ci ent determi ned by the characteri s tics of the watershed, "i" is the ra i n- <br /> <br />fall intensity at the time of concentration in inches per hour and "A" is <br /> <br />the watershed area in acres. <br /> <br />- <br />"CO was determined to be 0.60 from inspection of the watershed and <br /> <br />published values. This "c" value represents a hilly woodland, 10 percent to <br /> <br />30 percent slopes and tight clay. Since this watershed is composed of a <br /> <br />humis type soil overlying fractured rock, this "C" value is somewhat <br /> <br />conservative. The time of concentration for the watershed is estimated to be <br /> <br />0.15 hour from a nomograph relating channel length and elevation difference <br /> <br />to time of concentration. Rainfall intensity, "i" is 1.45 inches per hour <br /> <br />computed from data and methodology found in the NOAA Precipitation Frequency <br /> <br />Atlas for Colorado. <br /> <br />The peak 100-year discharge was determined to be 81.8 cfs using this <br /> <br />method. The average velocity through the watershed will be approximately <br /> <br />eight feet per second, however this peak will cascade over the rock channel <br /> <br />near the mouth of the watershed much faster. It wi 11 be necessary to con- <br /> <br />struct facilities to handle this high velocity flow without damage to the <br /> <br />site. <br /> <br />To check this peak discharge value, it was also computed using methods <br />found in the SCS Manual, Procedures for Determining Peak Flows in Colorado. <br />A 100-year 24-hour rainfall value of 3.8 inches was used. A SCS Curve Number <br /> <br />of 60 was used, representing hydrologic soil group B with 3 inches of humis. <br /> <br />40 percent ground cover and ponderosa pi ne. The runoff was 0.67 inches <br /> <br />6-2 <br />