9608

• UCREFRP Catalog Number: 9608
• Author: FLO Engineering Inc.
• Title: Establishment of a Green River Gage in Canyonlands National Park, Utah 1995-1996.
• USFW Year: 1997.
• USFW - Doc Type: Breckenridge, CO.
• Copyright Material: NO

' Discharge Frequency
Table 1 presents the discharge frequency for various return period floods at the Green
' River gage. The two-year return period flood prior to 1963 was approximately 31,000 cfs and
post-1963 was 20,700 cfs. Similarly the 100-year return period flood has been reduced from
69,000 cfs to 53,000 cfs. The decreasing trend in the frequency of high flow events began after
1930 (Figure 2). At Green River the standard deviation of the peak discharges before and after
1963 were 13,550 cfs and 9,720 cfs respectively or about a 28% decrease. For additional
discussion and plots of the frequency curves see the FLO report (1995b).

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Table 1. Green River Flood Frequency
for the Gage at Green River, Utah
Return
Period
' Probability ' Green River Gage (cfs)
Pre-1963 Post-1963
1.01 0.99 7,490 5,437
1.11 0.90 16,620 11,070
1.25 0.80 21,010 13,840
2.00 0.50 31,280 20,690
2.33 0.43 33,740 22,420
5.0 0.20 43,750 29,930
10. 0.10 50,920 35,840
25. 0.04 58,880 43,040
50. 0.02 64,100 48,210
100. 0.01 68,810 53,200
250: 0.004 73,080 58,060
500. 0.002 78,200 64,320
Mean Peak 32.;730 22,280
Mean Annual Flow ' 7,960 5,:620
''$ase Flow 2,720 3,380
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