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GREEN RIVER TRIBUTARIES BELOW FLAMING GORGE DAM PEAK FLOOD FLOW ANALYSIS Introduction. - The following stations were used in the determination of flood flows into the Green River from major tributaries: 1. Yampa River near Maybell, Colorado 2. Little Snake River near Lily, Colorado 3. Duchesne River near Randlett, Utah 4. White River near Watson, Utah 5. Price River at Woodside, Utah 6. San Rafael River near Green River, Utah For the stations with major upstream reservoirs, especially the Duchesne River with four upstream reservoirs, no attempt was made to remove the effects of regulation and study the unregulated peaks. The assumption is that the existing gauge record adequately reflects all the effects of regulation and that the log Pearson Type III distribution is the proper distribution. If these assumptions are not valid, then the resulting curves and computed return period flows for these stations may be substantially in error. Method of Analysis: Peak flow discharge information was obtained from the CDROM discs developed by Earthlnfo, Inc., and from recent Geological Survey records, where available. The following is a description of what was done for each gauging site: a. Yampa River near Maybell. Colorado - GS number - 09251000. The gauge has been in operation from 1904-1905, and from 1917-1995. The gauge is reflective of the runoff from 3410 square miles above the gauge. The average annual runoff past the gauge is 1,120,000 acre-feet. The records at the gauge are generally good.. The natural flow of river is affected by transbasin diversions, numerous storage reservoirs, and diversions for 65,000 acres above the gauge. The following reservoirs could impact the flood flows that pass the gauge: Stagecoach, Catamount, Yamcolo, Yampa, and Stillwater. These reservoirs account for 56,895 acre-feet of storage. Yamcolo, Yampa, and Stillwater have a combined total of 15,820 acre-feet. Stagecoach reservoir, built in 1988, has the most storage in the basin (33,275 acre-feet). The reservoirs should not have an impact on the larger peak flows for it is doubtful whether the diversions would be in operation during large floods. The annual peak flows vary from a high flow of 25,100 ft3/s on May 17, 1984, to the lowest annual peak of 3620 ft3/s on June 5, 1977. The earliest time that the peak flow has occurred during any water year is March 16th (1966). The latest the peak flow has occurred is June 19th (1949). In general, the peak rate of runoff occurs as the result of snowmelt with a large amount of the peaks occurring in the month of May and early June. Table 1 summarizes the recorded flows for the Yampa River near Maybell, Colorado, used in the analysis. Table 2 summarizes the results of entering the yearly peak flows for the period prior to 1988 into the FREQY computer model, developed by the Flood Hydrology Group, and letting the model compute natural