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Biological Opinions - Bureau of Reclamation

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UKL fill rate, water released for flood prevention, the volume <strong>of</strong> EWA that needs to be reserved<br />

for the base flow period (June through September), and the volume <strong>of</strong> EWA already used. This<br />

approach produces Link River Dam releases that will, when combined with accretions, provide<br />

flows at IGD that generally mimic the Williamson River hydrograph. When spill occurs or<br />

adherence to a minimum flow requirement causes releases that are not proportional to the<br />

Williamson River flows, the release at Link River Dam is adjusted for the next time step,<br />

restoring the proper proportionality.<br />

EWA will be distributed in accordance with the procedures and equations described below.<br />

“Will_prop_cum” is yesterday’s flow volume in the Williamson River as a proportion <strong>of</strong> the<br />

predicted Williamson River volume from today through September 30. Said another way, it is<br />

yesterday’s Williamson River volume as a proportion <strong>of</strong> the expected volume to come.<br />

“Fill_rate_ratio_spring” is a proportion expressing the relative progress <strong>of</strong> filling UKL by May<br />

31.<br />

“EWA_River” is the EWA determined on the 1 st <strong>of</strong> each month from March through June.<br />

“EWA_reserve” is the portion <strong>of</strong> the EWA reserved from use during the spring and subsequently<br />

used June through September.<br />

“EWAuseddv -1 ” is a cumulative variable beginning March 1 and adding the daily increment <strong>of</strong><br />

flow released as EWA.<br />

“C1_EXC -1 ” is yesterday’s flood prevention releases.<br />

“Net_LK_accrete -1 ” is yesterday’s net accretions between Link River Dam and Keno Dam.<br />

Flow in the Williamson River is the primary hydrologic indicator used to calculate a release<br />

target for Link River Dam during the spring. The initial calculated Link River Dam release<br />

target is modified based on the (1) fill rate ratio for UKL, (2) volume <strong>of</strong> EWA reserved for<br />

summer use, (3) spill from UKL for flood prevention, and (4) accretions to the Klamath River<br />

between Link River Dam and IGD.<br />

In all but extreme dry years, UKL is filling and continues to fill as the irrigation season begins,<br />

even as distribution <strong>of</strong> water to the Project and to the Klamath River increases. The<br />

Fill_rate_ratio_spring variable is designed to keep UKL on an appropriate trajectory to fill as<br />

hydrologic conditions change during the spring. The Fill_rate_ratio_spring reduces Link River<br />

Dam releases for EWA early in the irrigation season as UKL is filling. The influence <strong>of</strong> the<br />

Fill_rate_ratio_spring variable decreases steadily throughout the spring as UKL fills. Reducing<br />

29

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