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Final Report 1200 1100 1000 - ~ 900 C') E 800 - '" == 700 0 u: 600 ~ as CD 500 0.. C'I 400 s::: 'i: C. 300 en 200 100 0 3-13 September 2000 IliI Vampa River . Green River above Vampa Flaming Gorge Dam Completed ~ 0 N ~ ID ~ 0 N ~ ID ~ 0 N ~ ID ~ 0 N ~ ID ~ 0 N ~ ID ~ m m m m m ID ID ID ID ID ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ m m m m m m m m m m m m m m m m m m m m m m m m m m m m m ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Figure 3.5.-Contributions of the upper Green River and Yampa River to spring peak flows at the USGS stream gage near Jensen, Utah, 1947-1996. relative contribution of the upper Green River to the peak flow decreased. For the period of 1947 to 1962, the mean annual peak at Jensen was 680 m3/s. Since 1963, the mean annual peak has been reduced to 493 m3/s (FLO Engineering, Inc. 1997). Despite this reduction in the mean annual peak flow, the highest peak on record at Jensen (1,133 m3/s) occurred on 18 May 1984. The lowest annual peak on record at Jensen was 201 m3/s on 26 April 1989. This natural year-to-year variability in flows makes it difficult to make pre- and post-dam comparisons to illustrate the effects of Flaming Gorge Dam operations on flows. To understand the effects of operations, a simulated time series of daily unregulated flow was developed for this report (see Appendix A for a description ofthe approach used) and compared with gauged flow data during the same period. Unregulated flows for the period 1963 to 1996 were generated by using numeric modeling techniques in which the effects on flows from operating Flaming Gorge and Fontenelle Dams were removed and propagated to the Greendale, Jensen, and Green River gages. These modeled unregulated flows are used in this section to characterize the hydrology of the upper Green River basin and quantify effects of dam operations on Green River flows.