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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
PCWA proposes new pulse flows that would affect channel morphology and bed
surface textures in the bypassed. The pulse flows are designed to initiate gravel mobility,
scour the channel bed, and facilitate cottonwood and willow regeneration in the bypassed
reaches during wet and above normal water year types (PCWA, 2007b). Table 3.3.1-2
summarizes the schedule of pulse flow releases by water year type and reach. No pulse
flows are proposed in the Middle Fork American River downstream of Ralston afterbay
dam and in the peaking reach because natural high-flow events from unregulated river
inflows (e.g., North Fork of Middle Fork American River and North Fork American
River) and accretion in the reach provide the same functions as managed pulse flows in
these two reaches. The timing of pulse flow implementation following issuance of a new
license and the compliance points for measuring pulse flows (table 3.3.1-3) are outlined
in PCWA’s proposed Flow and Reservoir Monitoring Plan (discussed in detail in section
3.3.2.2, Aquatic Resources). PCWA also proposes to develop and implement a feasibility
study within one year of license issuance that identifies the maximum pulse flow between
200 and 600 cfs that can safely and reliably be released from the existing low-level outlet
at Hell Hole dam.
Table 3.3.1-2. Proposed and Alternative 1 (in parentheses when different from
proposed) pulse flow schedule for wet and above normal water years
(Source: PCWA, 2011a, and 2011b, as modified by staff).
Water Year Type
Above
Location Wet Normal
Action
May 1
Release a minimum of 150 cfs or inflow, whichever
May 7
(May 15) is less
May 2
May 8 Close diversion completely
(May 16)
Duncan Creek
below Duncan
diversion dam
May 11
(May 25)
May 13
(May 27)
May 16
(May 30)
May 19
(June 2)
May 23
(June 6)
Release a minimum of 190 cfs or inflow, whichever
May 10
is less (can reopen diversion)
Reduce the flow to a minimum of 130 cfs or inflow,
May 12
whichever is less
Reduce the flow to a minimum of 90 cfs or inflow,
May 15
whichever is less
Reduce the flow to a minimum of 45 cfs or inflow,
May 18
whichever is less
May 22 Release the minimum instream flow requirement
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