Biological Opinions - Bureau of Reclamation

16.6 Appendix F: Analyzing the relationship of Iron Gate Dam releases on water
temperature in the mainstem Klamath River during the spring
As described in this biological opinion (BiOp), NMFS has determined the Klamath Project
(Project) will reduce Klamath River flows below Iron Gate Dam during the spring. The River
Basin Model – 10 (RBM10) water temperature model was developed and calibrated for use on
the Klamath River by Perry et al. (2011) to help inform the Secretary of the Interior on the likely
changes to water temperatures that would be anticipated to occur should the four PacifiCorp
hydroelectric dams on the mainstem Klamath River be removed, as described under the Klamath
Hydroelectric Settlement Agreement (KHSA), and under instream flow management conditions
described in the Klamath Basin Restoration Agreement (KBRA). Perry et al. (2011) simulated
water temperatures over a period of 50 years using atmospheric and hydrologic data observed in
the Klamath Basin from 1961 through 2009 to project potential conditions 50 years into the
future from 2012 through 2061. This scenario is commonly referred to as the “index sequential”
simulation under the Secretarial Determination process to evaluate the potential impacts and
benefits that may occur under conditions described in the KHSA and KBRA. Future hydrologic
conditions simulated were based on flows described under NMFS’s 2010 BiOp (NMFS 2010)
and the KBRA (available at Klamathrestoration.gov). Since these results provide paired results
for differing flow releases from Iron Gate Dam, the RBM model was determined to be an
appropriate tool to help describe potential influence of discharge below Iron Gate Dam on water
temperatures during spring months, from March through June, when SONCC coho salmon fry,
juveniles and smolts are known to be present using the mainstem.
The RBM10 simulation assumes that the four PacifiCorp Dams are removed in 2020. Therefore,
for the purpose of evaluating the effect of flow on water temperature while dams are in place, the
results of the first eight years (2012-2019) are applicable to the proposed action period. The
RBM10 model results include mean daily water temperature (°C) and discharge (cfs) for several
nodes along the mainstem Klamath River between river from river mile 253 and the estuary for
each of two hydrologic conditions anticipated under the NMFS’s 2010 BiOp and the KBRA.
The paired results from these simulations allows for comparisons between the effects of different
discharge levels, when they exist under these two scenarios, on water temperatures downstream
of Iron Gate Dam.
Perry et al. (2011) found that the RBM10 generally performed well in predicting water
temperatures in the Klamath River, predicted water temperatures tracked observed water
temperatures well. The root mean square error for predicted water temperatures by reach ranged
from 0.81 to 1.46 °C and mean absolute error among locations ranged from 0.62 to 1.15 °C
(Perry et al. 2011).
For purposes of this analysis, only water temperature and discharge results for nodes present at
Iron Gate Dam (RM 190), the Shasta River (RM 176) and the Scott River (RM 143) were used.
To determine the change in water temperature (T-Delta) observed at each discharge, the mean
daily water temperature predicted at the confluence of the Shasta River and the Scott River were
each subtracted from the mean daily water temperature predicted at Iron Gate Dam. The rate in
which mean daily water temperatures change by river mile was also calculated by dividing the
change in water temperatures predicted by the number or river miles present between Iron Gate
Dam and the confluence of the Shasta River and the Scott River, respectively. Daily values for
each month were then averaged to derive mean monthly estimates for discharge, change in water
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