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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
years. The average duration of inundation (average days per year) would increase under
the proposed action by 8 days in wet years, by 9 days in above normal years, and by 8
days in below normal years. Similar to existing conditions, Area 2a would not be
inundated in dry or critical water years under the proposed action. Therefore, changes in
operations that affect the surface elevation in Hell Hole reservoir would result in only
minor changes in the frequency and duration of inundation in areas that support Stebbins’
phacelia in Areas 1 and 2a.
Table 3.3.3-6. Stebbins’ phacelia populations at Hell Hole reservoir that may be
affected by the proposed Hell Hole reservoir seasonal storage
increase (Source: PCWA, 2008a).
Area Definition
Area 1 At or below the current
maximum normal operating
water surface elevation of 4,630
feet down to about 4,605 feet
Area 2a Maximum normal operating
water surface elevation of 4,630
feet to 4,636 feet with
installation of 6 foot spillway
crest gates
Area 2b From 4,636 feet with
installation of 6 foot gate to the
maximum flood pool elevation
at 4,640 feet with installation of
10-foot gate
170
Area
(square feet) (acres)
No. Individuals
17,910 0.41 9,000–18,000
107,727 2.47 54,000–108,000
198,290 4.55 99,000–198,000
In Area 2b, which was not inundated in any water year type in the period of record
under existing conditions, portions of the area would be inundated under the proposed
action in years when Hell Hole reservoir spills (i.e., in 6 of 10 wet water years and in 1 of
6 above normal water years) during the growing season for Stebbins’ phacelia. The
average duration of inundation under the proposed action would be 22 days per year in
wet water years and 15 days in above normal water years. Similar to existing conditions,
Area 2b would not be inundated in below normal, dry, or critical water years under the
proposed action. Area 2b supports a substantially greater population size than that
supported by Area 2a and Area 1, potentially because current conditions are more
suitable in this area as opposed to closer to the water. Therefore, it is possible that there
would be a reduction in size of the population of Stebbins phacelia in Area 2b.