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

Application for New License Middle Fork American River Project (FERC Project No. 2079)
Overall no difference in the IBI or the individual BMI metrics was observable at the study
sites related to MFP operations or facilities, except at the study sites in the top of the
peaking reach immediately below Ralston Afterbay/Oxbow Powerhouse. The key
findings from the study are summarized below:
• In combination, the hydropower IBI and individual metric scores indicated lower
biological conditions at the top of the Middle Fork American River peaking reach
immediately below Ralston Afterbay Dam (MF24.4) and immediately below
Oxbow Powerhouse (MF23.6), compared to the adjacent sites on bypass rivers
(Rubicon and Middle Fork American rivers) and comparison sites (North Fork
American and North Fork of the Middle Fork American rivers). Fewer intolerant
EPT taxa, more high-tolerance individuals, and lower taxa richness were found.
• In the peaking reach, excluding the two sites at the top of the reach, biological
conditions (IBI and individual scores) were similar to those in nonpeaking
comparison sites (unimpaired comparison rivers and the Middle Fork American
River and Rubicon River immediately upstream of Ralston Afterbay) (some
variability occurred depending on the individual metric examined).
• Hydropower IBI scores were higher (indicating better biological conditions) at the
higher elevation, colder water sampling sites in the MFP study area than at the
lower elevation, warmer water sampling sites, suggesting that the hydropower IBI
was correlated with elevation and water temperature.
• Hydropower IBI scores downstream of French Meadows and Hell Hole reservoirs
were relatively high and within the range of those observed in unimpaired river
reaches above hydropower reservoirs by Rehn (2008).
• The hydropower IBI scores for the sampling sites both above and below the
diversions on South Fork Long Canyon and Duncan creeks were above the
median hydropower IBI scores for streams located upstream of dams and
diversions evaluated by Rehn (2008) (AQ 3 – TSR, Appendix D [PCWA 2011aa;
SD B]).
• Repeated annual sampling results from above and below Duncan Creek
Diversion did not indicate a consistent difference in hydropower IBI scores.
Productivity and Habitat Diversity
The methods used to characterize productivity and habitat diversity include wetted
perimeter, spatial niche habitat, and effective habitat (for fluctuating flows in the peaking
reach).
WETTED PERIMETER
Wetted perimeter and wetted bed versus flow relationships, useful for evaluating
potential effects of flow regimes on productivity (algae and benthos), were relatively
February 2011 5-12