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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
Monitoring Water Temperature in Project Waters
Project operations have altered the water temperature regimes in the large
bypassed and peaking reaches, particularly during the summer and early fall. Storage of
cold water in French Meadows and Hell Hole reservoirs during the spring runoff period
and its subsequent release from low-level outlets and powerhouses throughout the
summer and fall have reduced water temperatures of the Middle Fork American and
Rubicon Rivers by as much as 15°F or more compared with modeled unregulated flow
conditions (e.g., from low 60–70°F to mid 40–50°F).
Under existing conditions, mean daily summer water temperatures in most of the
project reaches are generally consistent with the basin plan beneficial uses for coldwater
freshwater habitat and habitat for reproduction and early development of fish, with two of
the river reaches (the downstream reach of the Rubicon River and the Middle Fork
American River downstream of Middle Fork interbay) exhibiting transition zones from
coldwater to warmer water habitat during the summer.
The proposed and Alternative 1 actions include modifications to hydrology (pulse
flows, increased minimum instream flows) in the bypassed reaches that could further
reduce water temperature. Decreased water temperature in the bypassed reaches would
potentially influence the location of the transition zones of coldwater and warmer water
species. Flows under both action alternatives are not anticipated to affect water
temperature in the peaking reach.
PCWA’s proposed Water Temperature Monitoring Plan describes methods and
analyses for collection of water temperature data at selected sites in bypassed and
peaking reaches associated with the project. The monitoring approach is based on the
approach taken in pre-application Commission-approved study plans. This information
would be used to characterize water temperatures within the monitored reaches over time
and to aid interpretation of biological monitoring data. Alternative 1, which includes
flows similar to the proposed action, would have similar effects on water temperature.
Alternative 1 also includes the proposed Water Temperature Monitoring Plan, although
no agency has offered recommendations or conditions pertaining to water temperature
monitoring.
Our Analysis
There would be little overall change in water temperature, compared with current
conditions, in the bypassed and peaking reaches under both the proposed action and
Alternative 1. Both alternatives would result in water temperatures that are substantially
lower in the summer and fall than under unregulated conditions and that are consistent
with basin plan objectives. Under the proposed and Alternative 1 actions, we consider it
likely that water temperatures in the bypassed and peaking reach would remain consistent
with the basin plan beneficial uses for cold freshwater habitat, warm freshwater habitat,
and habitat for reproduction and early development of fish. The natural warming of the
water along the length of the river reaches, similar to existing conditions, would also be
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