Biological Opinions - Bureau of Reclamation

For cumulative net inflow values between 280,500 and 340,000 acre-feet, the equation
determining the UKL elevation threshold = 0.02223x + 4133.6843 where x = the cumulative net
inflow into UKL since October 1 in thousand acre-feet.
For cumulative net inflow values greater than 340,000 acre-feet since October 1, the minimum
UKL elevation will be determined based on KBPM simulated results and observed hydrologic
conditions.
The points on the December graph defining the threshold, from low to high, are from water years
1993, 2002, and 1986.
Figure 8.4. UKL elevations at the end of January (kaf = thousand acre-feet).
In January, water years 1982, 1993, and 2006 are considered outliers because the UKL elevation
was less than expected for the cumulative inflow in those years, based on threshold shown in
Figure 8.4. January 1993 was a relatively low inflow month and followed the extremely dry
1992 water year. However, flood control releases were modeled by the end of March 1993
because a large snowpack had accumulated. Similar to December, water years 1982 and 2006
had high cumulative inflows and 2006 also had high inflow during January compared to the
POR. In similar situations during implementation of the proposed action, Reclamation will
consult with the Services regarding reasons for the lower than anticipated UKL elevations. The
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