THE RATIONAL METHOD FOR PEAK FLOW-RATE ESTIMATION

The Rational Method continues to be the most widely used approach for estimating T-year return frequency peak flow rates for small catchment s of about one square mile or less in area. The Balanced Design Storm unit hydrograph method is perhaps the second most widely used techniqu e for estimating peak flow rates (and is the most widely used method f or developing runoff hydrographs) but is generally considered to be mo re accurate than the Rational Method. In this paper, both of these T-y ear return frequency peak flow rate estimators are shown to be mathema tically comparable. The close similarity between these two approximato rs may help explain why the Rational Method continues to be widely use d even though other more computationally sophisticated techniques are readily available due to widespread computer software.