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MANUAL FOR ESTIMATING FLOOO CHARACTERISTICS 3 DESCRIPTION OF METHODS The three methods described below can be used for obtaining flood infor- mation at sites on natural-flow streams in Colorado. FLOOD INFORMATION AT GAGEO SITES Flood information at gaged sites is listed in the tables at the back of this report. Listed in the first line for each gaging station are the 10-, 50-, 100-, and 50D-year flood disch.rges and the 100-year flood depth based on the period of observed record. Gaging station locations are given as latitude and longitude in degrees, minutes, .nd seconds under each gaging station name. Because of the possibil ity of the observed period of record falling with- in a high or low climatic cycle, the data may not represent the best estimate for future periods of time. This possibility of error, called time-sampl ing error, is usually small for long periods of record but may be extremely large for short periods. A procedure described by Sauer (1974) reduces the effects of time-sampling errors by providing a weighted average of discharge from the station value and the regression value which is discussed on pages 5 and 6. The weighted average is computed from the equation QT(W)= (QT(S)XN) N + J.'::T(R)~ + E where the weighted discharge for recurrence interval T, QT(W)= QT(S)= QT(R)= N the station value of the flood for recurrence Interval T, the regression value of the flood for recurrence interval T, E the number of years of stat i on data used to compute QT(S) , and = the equivalent years of record for QT(R). A value of 10 years as recommended by the U.S. Water Resources Counci I (1975) should be used in the weighting procedure for all 9aged sites throughout Colorado. A weighted average was computed for each recurrence interval flood at all gaged sites and is I tsted below the station value in the tables, The weighted averages are the best estimates of future flood discharges of specified fre- quencies at gaged sites.