Biological Opinions - Bureau of Reclamation

eleases somewhat on the ascending limb of the UKL hydrograph functions to increase releases
on the descending limb of the hydrograph, which coincides with the timing of more intensive
upper Klamath Basin non-Project agricultural diversions that likely influence Williamson River
flows in the spring/summer. Therefore, the Fill_rate_ratio_spring simultaneously functions to
fill UKL and redistribute EWA releases to produce a more “normal-shaped” hydrograph in the
Klamath River later in the year.
During March through May, the EWA_reserve volume is subtracted from EWA_River, to retain
the reserve volume for subsequent use during the summer. However, no water is reserved when
UKL is spilling, or when releases at Link River Dam are made to meet minimum target flows at
IGD.
In June, UKL elevations are typically declining and the Fill_rate_ratio_spring variable is
dropped. The latter days of June also often mark the transition into the base flow period;
therefore, half of the EWA_reserve volume is subtracted from EWA_River instead of subtracting
the full volume.
( )
“IG_max” is the maximum flow target at IGD during July through September.
“Link_release_forIGmax” is the approximate release from Link River Dam necessary to produce
the “IG_max” flow at IGD.
“EWA_remain_JulSep" is the total remaining EWA for July through September.
During July through September, Link River Dam releases are the lesser of (1) the maximum IGD
flow target (Table 4.10), or (2) the average daily release for the remaining EWA volume. The
rationale for selecting the lesser of two options is that when IGD flow targets would be
exceeded, that water is not released, but is banked until October and November when it will have
greater ecosystem benefits.
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