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<br />. <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />records are available. For the areas of concern with the <br /> <br />Yuma study area, stream flow records are not available. <br /> <br />Consequently, this approach could not be used in conjunction <br /> <br />with this study. For purposes of this study, two methods of <br /> <br />calculating peak runoff were reviewed: The rational method <br /> <br />and the unit hydrograph method. Both methods are briefly <br /> <br />described in the following portions of this report. <br /> <br />4. RATIONAL METHOD <br /> <br />The most commonly used method of determining peak runoff <br /> <br />is the so called Rational Method. Widespread acceptance of <br /> <br />this method can probably be contributed more to its simplicity <br /> <br />as opposed to the reliability of the results. The rational <br /> <br />method provides an approximation of the peak rate of runoff. <br /> <br />It does not provide information relative to the streams time- <br /> <br />flow characteristics. Such characteristics are important <br /> <br />in analyzing large andlor complex drainage basins. <br /> <br />The basis of calculations for this procedure is the formula <br /> <br />Q=CIA. Where.9... equals the peak runoff in cubic feet per <br /> <br />second, A is the drainage area in acres, and I is the rainfall <br />- - <br /> <br />intensity at the time when all areas are contributing runoff <br /> <br />to the drainage system, and ~ is a coefficient related to the <br /> <br />characteristics of the drainage area under consideration. <br /> <br />10 <br />