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. . . usual use of this term should not lead to the conclusion that the event indicated can happen only once in x years, and having occurred, will not happen again for another period of x years. It means rather that over a long span of years, we can expect as many x-year floods (or larger) as there are x-year-long periods within that span. Floods occur randomly and may be bunched or spread out unevenly with respect to time, and predicting their distribution is not possible. The frequency of a particular flood event should be considered as the percent chance of an event of that magnitude (or greater) occurring in anyone year. A 100-year flood would therefore have a 1% chance of being equaled or exceeded in any given year. The PMF does not have a frequency value per se, although it is sometimes assigned a frequency value of 1,000 years for comparative analysis in frequency studies. It can be seen from the above definition of flood frequency that the PMF can occur the first year after a project is bui lt, although the odds are very heavily against it. G. 1. RESERVOIR SEDIMENTATION Sediment Yield Sediment inflow into the Webster Hill reservoir was estimated from USBR measurements of suspended sediment in the Colorado River at the Rulison Bridge, approximately 4 mi downstream from the dam site. The USBR measurements were made during the spring flood of 1979, when river flows ranged from 1,758 cfs on March 3 to 21,150 cfs on June 15. The 13 suspended sediment measure- ments taken by the USBR were plotted against the measured river discharges on a logarithmic scale, and a sediment rating curve was constructed by fitting two power functions to the data using the least squares method. An est imate of the average suspended sed iment load was computed by combining the data from the sediment rating curve with the flow duration data compiled from an analysis of the DeBeque and 3686-a/5 1-12