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<br />DRAINAGE CRITERIA MANUAL <br /> <br />RUNOFF <br /> <br />time distribution. The 1982 version of CUHP allows it to be used with basins . <br />as small as 90 acres if the engineer so desires. <br />A general characterization of the methods can be made as follows: <br />Rational Method. This method is recommended for storm sewer design and <br />overland flow from tributary basins generally less than 160 acres in <br />area. Storm sewer mains and outfalls that have tributary areas of more <br />than 160 acres should be sized by the CUHP method. The Rational Method <br />is applicable to both the major and initial storm runoff for basins up to <br />160 acres. <br />CUHP Method. This method is recommended for the design of storm sewer <br />outfa 11 sand larger ma ins where the bas in exceeds 160 acres, for the <br />design of most major channels and conduits, and for analyzing and <br />accounting for the benefits of storage. This method is particularly <br />applicable for areas which will undergo significant urbanization in the <br />future. <br /> <br />1.3 Future Runoff Analysis Modifications <br />When the manual was first prepared in 1969, it was planned to develop . <br />modifications to the coefficients as more field data are collected and <br />analyzed. By 1981, the Denver Urban Watershed Network had measured a large <br />nu~ber of flood events. While many of the events are relatively small, it is <br />possible to add more maturity in the flood design at this time. The data <br />acquisition will continue and additional modifications will evolve as more <br />data contribute to more understanding. <br /> <br />. <br /> <br />5-1-84 <br />