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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
Modifications to operations at Hell Hole reservoir could affect other riparian
resources on the reservoir shoreline and along tributaries that flow into the reservoir
because vegetation would be inundated more frequently, for longer periods of time, and
under deeper water. Operation changes could also reduce the amount of area for
establishment of riparian plants if water surface elevations are high when seeds are
dispersed and if water surface elevations continue to remain high through the growing
season. Riparian trees and shrubs are well adapted to surviving anoxic soil conditions
that may occur with prolonged inundation, although individuals may be susceptible to
drowning if the entire plant is inundated. The timing of reservoir draw-down would not
change under the proposed action. As noted in our analysis of Stebbins’ phacelia, there
would be little change in the inundation pattern at Area 1, and therefore little if any
expected change in the overall vegetative community in this area. The duration of
inundation in Area 2a would increase by from 8 to 9 days in wet, above average, and
below average water years, and in Area 2b by 22 days in wet and 15 days in above
average water years compared with existing conditions. Consequently, there is the
potential that, over the long term, the extent of riparian vegetation in Areas 2a and 2b
may be reduced, because of the increased duration of inundation under proposed
operations. In particular, young sprouts established below a water surface elevation of
4,630 feet and elevations of 4,630 and 4,636 feet may be affected. Under existing
conditions, riparian vegetation is present below water surface elevations of 4,630 feet)
that are inundated. The timing of reservoir draw-down would not change under the
proposed action. Therefore, distribution and abundance of riparian vegetation around the
reservoir under the proposed action likely would be maintained compared with existing
conditions. However, it is also possible that the extent of riparian vegetation at Hell Hole
reservoir, in particular in Areas 2a and 2b, would be reduced. Implementation of
vegetation monitoring in in both the proposed and Alternative 1 VIPMPs would enable
documentation of the actual effects of the future Hell Hole reservoir management on
riparian vegetation and whether remedial measures may be warranted.
Effects of Proposed Changes in Project Facilities on Vegetation
The effects of proposed facility modifications related to sediment management are
addressed in the previous subsection. In addition, the PCWA proposed and Alternative 1
Recreation Plans both call for the removal of two campsites at Hell Hole Campground,
and all 13 campsites at the Upper Hell Hole Campground. A population of about
47,000–94,000 individuals of Stebbins’ phacelia is documented at a recreation area at
Hell Hole Vista, which currently undergoes vegetation management, road maintenance,
and recreation facility maintenance. PCWA also proposes to reduce the area where
routine vegetation management and heavy recreation facility maintenance activities
would occur at Hell Hole Vista from 2.2 to 0.4 acre to reduce the size of the project
footprint on a population of Stebbins’ phacelia.
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