Draft EIS_072312.pdf - Middle Fork American River Project ...

20120723-4002 FERC PDF (Unofficial) 07/23/2012
all water year types are generally lower from January through June and higher during the
rest of the year. This trend is evident under existing and proposed operations of the
Middle Fork Project.
Water Temperature
As discussed earlier in this section, storage of cold water in French Meadows and
Hell Hole reservoirs during the spring runoff period and its subsequent release from lowlevel
outlets and powerhouses through the summer and fall have reduced water
temperatures of the Middle Fork and Rubicon Rivers by 15 o F or more compared to
unregulated conditions. Diversion of flows by the four other projects discussed in the
previous subsection can also influence water temperature by diminishing flows in
bypassed reaches making remaining flows more susceptible to solar warming or shielding
water from solar water by passing it through flow conduits.
PCWA modeled the cumulative effect on water temperature of the existing and
proposed project coupled with the other four projects that influence flows upstream of
Folsom reservoir. The modeling showed that the mean monthly water temperature at the
Folsom reservoir high water mark in a wet water year would be lower from June through
September under the proposed action compared to existing conditions, with the most
pronounced difference, about 2 degrees Celsius ( o C), occurring during August. Under
both existing conditions and the proposed project, the mean monthly water temperature at
Folsom reservoir from May through September would be less than 17 o C. Modeling of
dry water year temperatures showed that proposed project operations would result in
mean monthly water temperatures at Folsom reservoir from 1 to 2 o C lower during June,
July, and August, compared to existing conditions. Under both existing conditions and
the proposed project, the mean monthly water temperature at Folsom reservoir during a
dry year would be less than 20 o C. Therefore, operating the project under PCWA’s
proposed flow regime would have a positive cumulative effect on water temperature
downstream of Oxbow powerhouse by serving to reduce water temperatures, thus making
the affected stream reaches more suitable for trout. This could have important
ramifications if Central Valley steelhead should be reintroduced upstream of Folsom
reservoir.
Central Valley Steelhead
Nimbus dam on the American River currently blocks upstream migration of all
anadromous fish, preventing access to reaches affected by the Middle Fork Project.
Since Nimbus and Folsom dams were constructed, two new barriers to upstream fish
passage have developed in the peaking reach downstream of the project—“Tunnel
Chute” at RM 22.9, which was created by mining activity in the 1880s and “Ruck-a-
Chucky rapids” at RM 10.8, created by a landslide in the 1940s. A plan for reintroducing
steelhead upstream of Nimbus and Folsom dams and into the upper American River
watershed was included in the Biological Opinion for Long-term Operations of the
Central Valley Project and California State Water Project (NMFS, 2009b), and NMFS
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