FERC Project No. 2079 - PCWA Middle Fork American River Project ...

Application for New License Middle Fork American River Project (FERC Project No. 2079)
lower optimum 6
water temperature) transition and the 20°C (trout upper water
temperature) transition occurs are shown in BA/BE Tables 33a–b. The greatest
difference/change in the location of the 17°C transition is 0.1 mile, and no change
occurs in the location of the 20°C transition.
For the Rubicon River, the location of the 17°C transition under the Proposed Action is
similar to the No-Action Alternative in dry and below normal water year types, but is
approximately one mile downstream in critical year types due to the increased minimum
flow of 5 cfs in the critical water year type under the Proposed Action (10 cfs existing
versus 15 cfs Proposed Action). Under the Proposed Action, the 20°C water
temperature transition is 1.9 to 2.58 miles downstream compared to the No-Action
Alternative, depending on water year type (BA/BE Table 33b).
Wetted Perimeter
The Proposed Action specifies higher MIFs and provides pulse flows that increase
wetted perimeter. The effects of the MIFs on wetted perimeter are quantified below for
three seasons in the bypass reaches (spring, summer/fall, and winter) and for four
seasons in the peaking reach (spring, summer, October outage, and winter). In the
bypass reaches, the percent change in the 50% exceedance value (median) of wetted
perimeter is compared to the No-Action Alternative and the Existing License Condition
for each water year type. The median value of wetted perimeter was derived from a
daily time series analysis using the wetted perimeter versus discharge relationships in
the AQ 1 – Instream Flow TSR (AQ 1 – TSR) (PCWA 2011y; SD B). In the peaking
reach, the percent change in wetted bed area at the 2D modeling sites was used
instead of wetted perimeter (wetted bed area is a readily available metric from the
2D models).
The analysis shows that the Proposed Action maintains or enhances wetted
perimeter/bed area in all river reaches (BA/BE Tables 34 and 39) as discussed below,
by season.
• Spring. Wetted perimeter increases approximately 10% or more at the top of the
bypass reaches due to the increased MIFs in the Proposed Action compared to
the No-Action Alternative. Spring wetted perimeter enhancement is less in the
lower end of the bypass reaches because natural accretion augments the
minimum flows such that the incremental effect of the increased minimum flow is
reduced (i.e., “dilutes” the effect of the increases in minimum flow). In the
peaking reach the average increase in wetted perimeter is 12%.
6 Water temperature identified by FYLF experts, Dr. Amy Lind, USDA-FS and Dr. Sarah Yarnell, Cardno
ENTRIX, as the approximate lower optimum summer (July through August) water temperature range for
FYLF, which also corresponds approximately to the upstream distribution of FYLF in the Rubicon River
and the Middle Fork American River.
February 2011 6-20