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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
Minimum Instream Flows
Various flow elements associated with hydroelectric project facilities and
operations (e.g., minimum flow, pulse flows, ramping rates) can affect the aquatic and
riparian environment. Reduced flow and less seasonal variation in flow associated with
operation of project reservoirs and diversions may affect aquatic biota and aquatic
habitat, as well as users affected by instream flows (e.g., recreational visitors, addressed
in section 3.3.4, Recreation and Land Use, and power generation, addressed in section 4,
Developmental Analysis). Flows that support optimal conditions, however, can differ
significantly among these resources and users.
PCWA’s proposed instream minimum flow regime for project bypassed reaches
and the peaking reach is shown in table 3.3.2-8. Alternative 1 minimum flows are similar
to the proposed minimum flows and are consistent with Forest Service condition no. 22,
with the exception of the peaking reach minimum flows (which are generally from 15 to
100 cfs higher than comparable months and water years under the proposed minimum
flow regime) and minor differences associated with PCWA rounding flows to the nearest
0.5 cfs whereas Alternative 1 (and the Forest Service) generally uses only whole
numbers. Other differences between the proposed minimum flow regime and Alternative
1 include the following:
• Alternative 1 specifies that minimum instream flows be released by 5 p.m.,
while PCWA proposes that minimum instream flows be released within 5 days
of the dates specified in a new license. In both cases, exceptions would be
allowed when access to the instream flow release infrastructure would be
prohibited by weather or hazardous conditions.
• Alternative 1 states that hourly running average flow measurements would
never be less than the thresholds specified in a new license, except as
authorized in advance. PCWA would maintain instantaneous flows at all times
to be no less than 90 percent of the required minimum instream flow and
maintain daily average flows to be equal to or above the minimum instream
flow requirements on all days. PCWA proposes that instantaneous flow would
at all times be no less than 90 percent of the required minimum instream flow
and that daily average flow would at all times be no less than 90 percent of the
required minimum instream flow. Deviations that are less than 10 percent of
the required minimum instream flow would be corrected within 3 days of
discovery by releasing the equivalent volume of under-released flow into the
affected stream reach.
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