Biological Opinions - Bureau of Reclamation

Figure 11.9. Regression between EWA volume allocation and March through September NRCS
reconstructed UKL inflow forecast volume.
11.4.1.1.2 Annual Hydrograph
When compared to the observed Keno hydrograph for the POR, the proposed action hydrograph
at Keno trends towards the historic Keno hydrograph from 1905-1913 (Figure 11.4). When
compared to the POR, peak flows under the proposed action will occur approximately two weeks
closer to the historic peak flow at Keno (Figure 11.4). Overall, under the proposed action, water
will be shifted from the fall and winter period to the spring and summer period resulting in
enhanced spring flows, a more gradual receding limb of the hydrograph, and enhanced summer
base flows compared to the observed POR hydrograph (Figures 11.4 and 11.5). This
redistribution of water is important because the proposed action ultimately shifts more water to
the critical spring and summer period for life history stages of coho salmon than observed in the
POR. Consequently, the proposed action hydrograph at IGD trends towards the natural flow
regime relative to the observed hydrograph at IGD for the POR, however both the proposed
action and observed hydrographs have been reduced relative to the natural hydrograph (Figures
11.4 and 11.5).
Compared to the observed hydrograph for the POR at IGD, flows under the proposed action
begin lower in the fall and winter period, peak later in the spring, and maintain higher flows
during the spring and summer period (Figure 11.5). Additional patterns evident under the
proposed action are enhanced flow variability in fall and winter, and increased spring and
summer flows during the descending limb of the hydrograph relative to the POR (Figure 11.5
and Appendix E). To illustrate these patterns also exist on an annual basis, NMFS compares the
proposed action flows at IGD to the observed flows at IGD from March 2010 through September
2011 (Figure 11.10). In October through February 2011, the proposed action results in increased
flow variability and magnitude below IGD. Additionally, the proposed action results in a higher
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