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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
natural hydrologic regime and improved sediment supply and transport downstream of
project facilities. Implementation of these actions would: (1) restore natural sediment
supply and transport downstream of the small diversions and enhance sediment supply
and transport downstream of the medium dams; (2) preserve the frequency of high
magnitude scouring (“re-setting”) flows in river and stream reaches; (3) restore riparian
recruitment flows in wet and above normal water years by providing pulse flows with
natural recession rates and more natural downramping of spills; and (4) provide higher
minimum flows, particularly during the spring, summer, and fall. In a few areas,
however, riparian vegetation may be temporarily or permanently affected during
implementation of the proposed measures.
Project-related changes in flows to the bypassed and peaking reaches could affect
plants adjacent to such reaches. Populations of five special-status plants (Brandegee’s
clarkia, Butte County fritillary, Red Hills soaproot, saw-toothed lewisia, and Stebbins’
phacelia) were documented within 200 feet of bypassed or peaking reaches. However,
these populations grow primarily in rocky areas on the steep river canyon walls and in
upland canyon live oak woodlands, both of which are elevated above the wetted
perimeter of the bypassed and peaking reaches. Some of these populations may
experience inundation during infrequent, high-magnitude flows under existing conditions
and all action alternatives.
Modification of existing facilities and construction of new facilities, including the
small diversion modifications (i.e., modification of the small stream diversion dams into
self-cleaning, stream-bottom intakes), and outlet works modifications could potentially
affect riparian resources either by direct loss of riparian individuals and/or degradation of
habitat. Construction activities associated with the modification of existing facilities
would result in the following:
• At Duncan Creek diversion pool, about 0.03 acre would be permanently
removed for construction of the modified dam structure.
• At South Fork Long Canyon Creek diversion pool, about 0.01 acre of willows
and alders would be permanently removed for construction of the modified
diversion structure.
• At Hell Hole dam outlet works, re-contouring of the Rubicon River channel in
proximity (about 650 feet) to the outlet works to accommodate the pulse flows
would remove about 0.24 acre of riparian vegetation.
However, because riparian vegetation would be re-planted following completion
of the re-contoured Rubicon River reach, effects at Hell Hole dam outlet, which account
for the majority of the area that would be disturbed for these construction activities (i.e.,
0.24 acre out of 0.28 acre total) would be temporary.
At the Duncan Creek and South Fork Long Canyon Creek diversion pools,
riparian vegetation would be removed if it should be impeding operations of the diversion
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