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<br />plistic from the standpoint that rainfall is assumed to <br />occur u:1iformly over the ,'Iatershed both spatially and <br />tempora:.ly. With this assumpticn, it can be shown that <br />the maximum peak discharge will be obtained when the <br />rainfall duration is selected for a time equal to the <br />time of concentration. Because of the idealistic <br />assumptions of the Rationall Formula methodology, the <br />method is generally considered to be applicable to <br />catchments of 200 acres or less. The time of concentra- <br />tion is a measure of the response time of a watershed <br />and is jirectly related to the time to peak variable <br />used in the SCS a.nd CUHP methodol09ies. The time of <br />concentJ:ation is defined .1:0 be the time required for <br />water to travel from the most remote point within the <br />watershed to the point under consideration in the <br />watershe,d. Various empiric:'~l methods are available for <br />estimat~on of the time of concentration for a water- <br />shed. 'I'hese will be discussed in the t;wo examples that <br />are presented. It is noteworthy that the results of <br />the Rational Formula calculation are always provided in <br />cubic feet per second (cfs) even though the actual <br />uni,ts obtained from the equation are acre--inches per <br />hour. This would seem to be dimensionally inconsist- <br />ent, however, 1 acre-inch per hour is approximately <br />equal to 1 cubic foot per second so no mathematical <br />conversion is required. A simple application of the <br />Ration Formula Methodology ,rill be pJ:esented. <br /> <br />References (Continued) <br /> <br />8) Wright McLaughlin Engineers, 1969, Urban <br />storm Drainage Criteria Manual, Volume 1, <br />Denver Regional Council of Governments, <br />Denver, Colorado. <br /> <br />9) U.S. Department of Agriculturet Soil Con <br />servation Service, National Engineering <br />Handbook, section 4, Hydrology (Amendment 6), <br />1985. <br /> <br />l;:~ <br />