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

Application for New License Middle Fork American River Project (FERC Project No. 2079)
monotonic in their rate of increase in wetted perimeter with flow in the bypass and
peaking reaches. The rate of increase in wetted perimeter with increased flow was
greatest at the lowest flows and least at the highest flows. However, the relationships
typically did not have distinct inflection points (distinct breaks) where an increase in flow
exhibited an obvious change in the wetted perimeter relationship. Plots showing these
relationships are available in Exhibit E – Appendix B2 (also see AQ 1 – TSR,
Appendix M [PCWA 2011y; SD B]).
SPATIAL NICHE HABITAT
Physical habitat (niche) utilization for different species and life stages is summarized in
BA/BE Table 29. The spatial niche habitat versus flow relationships for each of the
instream flow study sites are found in Exhibit E – Appendix B2. In the small streams,
shallow water habitat was the dominant niche over a wide range of flows, while
moderately deep water niche habitat was dominate in the large rivers. The diversity of
spatial niche habitat types was least at low flow and generally greatest at intermediate
flows. At low flow, shallow and/or slow velocity habitat was dominant at each of the
study sites. As flows increased, deeper and faster water niches increased as a relative
percentage of the total amount of habitat. At the highest flow, deep/fast water became
the dominant habitat type. Generally, the diversity of habitat is positively related to the
diversity of fish species and life stages in rivers. Several investigators have shown that
species and life-stage diversity is directly related to stream hydraulics and the spatial
diversity and stability of habitat (e.g., Gorman and Karr 1978; Statzner and Higler 1986;
Schlosser 1987; Bain et al. 1988; Allan 1995; Bowen et al. 1998).
EFFECTIVE HABITAT (FLUCTUATING FLOWS IN THE PEAKING REACH)
Flow fluctuations related to hydroelectric generation peaking have the potential to
reduce overall productivity of rivers (Morgan et al. 1991; Cushman 1985; Gislason 1985;
Moog 1993; Bain 2009) and to affect the diversity of aquatic species and/or abundance
of juvenile life stages (especially shallow, slow water species and life stages) (Bain et al.
1988; Kinsolving and Bain 1993; Scheidegger and Bain 1995; Bain 2009). Many
aquatic species have specific habitat requirements and limited mobility (e.g., Edington
1968) and daily flow fluctuations modify the location and amount of habitat (depths and
velocities and/or location of the channel margin), thereby, decreasing overall habitat
quality and availability.
The effective habitat flow matrix tables and associated plots are presented in Exhibit E –
Appendix B2 (also see AQ 1 – TSR, Appendix M [PCWA 2011y; SD B]) for the peaking
reach study sites (MF4.8 and MF14.1). The effective habitat matrix results show that for
low mobility species/life stages, such as macroinvertebrates (food production), changes
in flow cause a large reduction in habitat Figures 43 and 50 in Appendix B2. For
example, at Fords Bar (MF14.1) the amount of food production habitat available at
1018 cfs would be reduced by 56% if flows fluctuate down to approximately 100 cfs
(107,696 to 47,017 feet^2/1000 feet). Under this same scenario, the food production
habitat at Buckeye Bar (MF4.8) would be reduced by 69% (90,811 to 28,151
feet^2/1000 feet).
February 2011 5-13