THE PONDS PROJECT - Sustainable Conservation

population. Under that scenario, the long-term February median flow could be an
adequate bypass flow despite a CFII of more than 10 percent at a POI.
To investigate this possibility, a qualified fishery biologist can survey (or
otherwise quantify) spawning and rearing habitat within the watershed at points
upstream and downstream of POI’s where CFII is greater than 10 percent. The
results of such a survey would identify those spawning habitats most likely to be
adversely affected by cumulative water diversions, and it would quantify
available spawning habitats not likely to be adversely affected by cumulative
water diversions.
If credible site-specific biological data can demonstrate that minor reductions in
available spawning habitat will not adversely affect salmonid populations, then it
may be concluded that a diversion bypass flow equivalent to the February median
flow poses no adverse affect to salmonid spawning habitat. To reach that
conclusion, it would be necessary to provide biological data that demonstrates that
the remaining available spawning habitat is clearly not limiting production of
salmonids immediately downstream and in the vicinity of the diversion project.
3. In situations where substantial amounts of potential spawning habitat in small
watersheds are adversely affected by cumulative diversions, a qualified fishery
biologist can assess the bypass flows needed to protect spawning habitat using the
Instream Flow Incremental Methodology or other suitable methods for evaluating
streamflows needed to protect fish habitat (Bovee 1982; EPRI 1986; Annear et al.
2002). As discussed above, to ensure acceptance of the methodology and field
study results, we recommend such studies be done in consultation with CDFG and
NMFS.
Bypass Flows for Anadromous Salmonid Passage
When CFII is greater than 10 percent downstream from a diversion site, project
proponents should evaluate impacts to upstream fish passage. High rates of water
diversion can adversely affect fish passage by reducing stream depths in shallow riffles,
steep gradient cascades, and artificial barriers. As flows recede, the flow at which
passage opportunity becomes compromised is generally dependent on local hydraulic
conditions and site specific features. The objectives of the fish passage assessment
should be to identify flows that are adequate for upstream passage of adult salmonids and
to determine the adequacy of the long-term February median flow for facilitating
passage. If not, a higher minimum flow may be needed.
Bjornn and Reiser (1991) discuss the issue of upstream migration of salmonids and
approaches for evaluating the suitability of stream flows for successful passage.
Effective passage flows are generally determined through site-specific studies that
involve measurements at alternative flows. Thompson (1972) describes one approach for
identifying suitable passage flows based on empirical measurements at transects across
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