Mainstem Passage Strategies In the Columbia River System: Transportation,
Spill, and Flow Augmentation (aka "Giorgi Report")
January 31, 2002 | document 2002-3
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Executive Summary
The National Marine Fisheries Service 2000 Biological Opinion (BO) for
the Federal Columbia River Power System (FCRPS) prescribes guidelines for
smolt transportation, spill and flow augmentation to improve survival of
salmonid stocks listed under the ESA. With respect to these strategies the
NPPC is concerned about the following issues:
- What does the scientific literature inform us regarding the
benefits, shortcomings, or risks associated with each passage
strategy, and as compared to other passage options?
- Which aspects of the scientific information are in dispute?
- What are the critical uncertainties attending each strategy?
- What is being, or could be done to reduce uncertainty and disputes?
In terms of scope, the NPPC seeks information for both ESA-listed and
unlisted salmonid populations across a range of water years. The Council
seeks clear, concise and succinct treatment of these issues. Our approach
is to review key research and analyses that have appeared in the
literature, then distill out the key findings and synthesize the results.
The focus is on evaluations conducted under contemporary river operations,
which were initiated in the early 1990s and formalized as guidelines in
the 1995 and 2000 Federal Columbia River Power System Biological Opinions.
Additionally, we identify key uncertainties and gaps in the information
base, and identify research that is in place or planned to fill those
gaps.
Smolt Transportation
Using general, annual indices of performance, both NMFS and CBFWA
analyses showed that the majority of the time, fish transported from Lower
Granite and Little Goose dams produced TIRs higher than or equal to
corresponding inriver control groups. Bouwes et al. (2001) concluded
modest transportation benefits were evident for hatchery chinook, and
slight to negligible benefits for wild fish. Sandford and Smith (in press)
state that, "once a juvenile fish is entrained in a bypass system at
a "collector dam", transporting the fish maximizes the
probability of its eventual return as an adult." Based on assessments
by those two investigations, it appears that there is a survival advantage
associated with transporting Snake River hatchery spring/summer chinook
and steelhead, particularly from the upper two dams, Lower Granite and
Little Goose dams. However, the rationale for transporting smolts from
Lower Monumental and McNary dams is less clear. The benefits of
transporting Snake River hatchery fish from those dams are equivocal.
In some years, small sample sizes have resulted in poor or undefined
precision for key estimates. This can limit the ability to make
statistically defensible conclusions. Authors examining recent estimates
do not confidently state that transported fish survive at significantly
higher rates than inriver counterparts. Neither Sandford and Smith (in
press), nor Bouwes et al. (2001) explicitly tested key hypotheses such as;
D > Vc, or TIR > 1.0. Presumably future analyses by these two
research groups will do so. In recent times the resurgence in adult
returns offers improved precision and opportunities for meaningful
statistical tests
Whether or not wild fish respond favorably to transportation is
difficult to ascertain at this juncture. Even though the limited numbers`
of evaluations indicate higher return rates for transported smolts, the
estimates are based on such small sample sizes that the precision for wild
fish is particularly poor. Thus, reliance on the point estimate as a
representative value is questionable.
Survival from smolt to returning adult (SAR) for hatchery and wild
spring summer chinook has increased substantially since 1993, and has been
increasing steadily from 1997-1999, reaching SAR levels in 1999 that
approach and in some cases exceed the 2% minimum recovery threshold for
wild stocks as identified in PATH. This suggests that neither transport
nor inriver migration conditions may be a bottleneck to recovery, when
marine-based survival is at some adequate level.
No mass transportation study has been conducted that targets Snake
River fall chinook. Such evaluations are warranted, and planned for
initiation in 2002
There is evidence to suggest that homing fidelity may be impaired for
some species of transported fish, including fall chinook, sockeye, and
steelhead. Studies that target spring/summer chinook and steelhead require
emphasis. Straying may in part contribute to delayed effects associated
with transporting smolts. It may be advantageous to ascertain the extent
of straying associated with transport of all species to address certain
ESA concerns. Excessive straying may result in increased hatchery fish
intermingling among wild adults on the spawning grounds. This may not be
desirable. Ongoing telemetry/PIT tag-based studies of adult passage should
offer additional insight on this matter.
Delayed differential effects relative to inriver migrants are
consistently evident for transported fish. However, by-and-large adult
return rates to Lower Granite Dam exceed those of inriver migrants
designated as controls. In such cases, there would still be a survival
advantage to transport Snake River fish from Lower Granite and likely
Little Goose dams.
Spill
Apart from the Snake River stocks, which can largely be transported,
the majority of smolts emanating from the rest of the basin continue to
migrate in-river to below Bonneville Dam. Optimizing smolt survival during
downstream migration has been a longstanding goal of fisheries managers.
We focus on contemporary passage survival estimates and estimation
techniques (balloon-, radio-, and PIT-tag methods) developed during the
1990's that continue to be applied this decade.
The collective information indicates that spillways appear to be the
safest passage routes available at dams, even more benign than many smolt
bypass systems, particularly those involving the screening of turbine
intakes. The magnitude of smolt survival through spillways varies across
dams and species. This is particularly evident when total effects are
reflected in the empirically obtained estimates. This suggests that
species- and dam-specific estimates should be updated for each dam and
applied in any future passage modeling analyses. Spillway flow deflectors
(gas abatement devices) appear to increase smolt mortality relative to a
standard spillbay, by 1-3 percentage points. Even so, survival will
typically still exceed the turbine route at most dams. The potential for
increased smolt losses at the concrete needs to be balanced against gains
associated with gas abatement. It is not clear that passage models
currently provide an accurate assessment of this tradeoff.
Studies assessing the direct and total effects associated with spillway
passage indicate that survival is related to discharge at some sites, with
mortality increasing at excessive discharge volumes. The difference in
survival across discharges can range from negligible to nearly 7
percentage points, depending on the dam and species.
In passage modeling analyses, values for model parameters should be
periodically updated for each dam and species. The set of empirical
estimates that characterize smolt passage survival through spillways, as
well as spill efficiency, are being continually expanded. However, that
collective information is not being systematically compiled and
synthesized on a regular basis for the hydrosystem at large. Notable
exceptions include papers by Muir et al. (2001a), Ploskey et al. (2001)
and Anglea et al. (2001) for selected sites.
Passage modeling may afford the only practical means to evaluate the
relative benefits of various spill scenarios, at the level of the overall
smolt population. The other approach requires obtaining reliable empirical
survival estimates linked specifically to spill conditions. This requires
a well-designed experimental protocol that will likely be very difficult
to implement in this complex system of competing uses
The NMFS Total Dissolved Gas standard of a maximum 120% saturation in
the tailrace of Columbia River dams is generally achievable by following
the dam-specific gas caps identified in the Biological Opinion, and
implementing the spill program currently in place in the Mid-Columbia. The
exception occurs in higher flow years when spill volumes cannot be
effectively controlled due to flows exceeding the hydraulic capacities at
the various dams. The standard appears satisfactory for protecting
salmonid species within the hydro-system, but it exceeds water quality
guidelines established by the Environmental Protection Agency.
The full biological impacts of a spill program have not been evaluated
in their entirety. Smolt survival receives emphasis. Model analyses try to
predict changes in smolt survival to below Bonneville Dam. Quantitative
system analyses have not formally addressed the potential for impacts on
adult mortality. Empirical evaluations conducted in situ, have limitations
as well. For example those recently conducted by Zabel et al. (in press)
and FPC (2001) observed changes over small segments (projects), thus
cumulative effects through the system are not evident. Furthermore,
results from empirical evaluations are equivocal, because spill effects
have not been clearly isolated from other factors.
The effects of spill operations and levels on adult passage behavior as
linked to long-term survival are not well understood. Some of the recent
adult passage research suggests that higher spill volumes may exacerbate
migration delay and fallback. But, convincing quantitative relationships
have not been developed. Adult passage studies are continuing and may
provide insight on these matters.
Flow Augmentation
Flow augmentation (FA) is the intentional release of water from storage
reservoirs for the purpose of increasing flows to enhance migratory
conditions for juvenile and adult life stages of salmonids in the Snake
and Columbia rivers. Flow augmentation provided to the upper Columbia
River (downstream from Chief Joseph Dam) comes from large storage
reservoirs such as Grand Coulee Dam and a complex of storage reservoirs
that drain into it from Canada and Montana. In the Snake River flow
augmentation is provided from Dworshak Dam and through the Hells Canyon
Complex in Idaho. The foundation for prescribing such actions is based on
two premises:
- Increased water velocity
increases migration speed of smolts
increases survival.
- Lowering water temperature (summer)
improves migratory and rearing conditions for both juvenile and adult
salmonids
results in improved survival.
Information obtained or reported since the early 1990's is the focus of
this report, but a brief historical backdrop is provided where needed.
Both river operations and the mark-recapture tools and associated
analytical procedures have changed markedly from previous decades. Thus,
the contemporary information is most applicable today.
Flow effects on smolt migration speed: For most spring-migrating
species the evidence indicates that increased flow (water velocity)
contributes to swifter migration speed. Information regarding fall chinook
is equivocal.
- River discharge appears to be the most influential variable
affecting migration speed of steelhead and sockeye salmon in the Snake
and mid-Columbia rivers.
- Two factors, flow and the degree of smolt physiological development,
explain the observed variation in the migration rate of yearling
chinook salmon (except in the mid-Columbia where only smolt
development has been identified as a predictor variable).
- At least four variables have been implicated as influencing the
migration speed of sub-yearling (fall or summer/fall) chinook; flow,
water temperature, turbidity and fish size. However, strong
correlations among these predictor variables confound the ability to
identify causative agents.
Flow effects on smolt survival: PIT tag based smolt survival
estimates acquired since 1993 provide the most relevant data set for
characterizing smolt survival dynamics through the impounded mainstem
Snake and Columbia rivers.
- Based on recent PIT tagged based estimates there is little evidence
supporting a flow survival relationship across the water years
experienced from 1993-2000, for yearling chinook or steelhead.
- However, in 2001 under the extreme low flow conditions, steelhead
survival decreased dramatically to about 63% per project (typically it
is near 90%). Slow migration speed and rapidly increasing water
temperatures are implicated as causative factors affecting
residualization and mortality.
- A complex of factors is implicated as influencing Snake River fall
chinook survival including, flow, water temperature and turbidity.
These environmental variables are strongly correlated during the
summer migration, confounding the ability to identify the most
influential one. Knowing if water velocity or temperature is the most
influential could be important when the decision is to use Dworshak or
Hell's Canyon for flow augmentation, since the temperature of those
water sources differs greatly.
The premise for reducing summer water temperature, particularly in the
Snake River, to improve rearing and migratory conditions for juvenile fall
chinook and adult salmonids appears sound.
- The literature indicates that maintaining river temperatures at or
below 20?C is advantageous to both life stages of fall chinook, and
adult steelhead, all of which are in the river in August and early
September.
However, it is not clear that releasing cool water from Dworshak
effectively alters the thermal structure of most of the Lower Snake River.
The major effect is localized at two upper reservoirs (LGR, LGO) according
to results reported by Bennett et al. (1997).
- When cool water enters the reservoirs it sinks to the bottom. This
can provide cool refugia in deeper waters, but not uniform cooling of
reservoirs.
- The greatest change in temperature attributable to FA releases from
Dworshak are evident at LGR, where water temperatures under FA are
predicted to be as much as 4-8 ?F below base conditions at certain
times. At Ice Harbor the difference is on the order of 1-2 ?F.
Flow Augmentation Evaluations are generally lacking. Only a handful of
studies have attempted to:
- Quantify the volume and shape of water provided specifically as FA.
- Translate that incremental increase in flows to changes in water
velocity and temperature.
- Predict the change in smolt travel time and survival attributable to
those increases
- Identify whether populations of interest (e.g. ESA stocks) have
encountered FA events.
The last such evaluation treated information through the 1995 water
year, and only for the Snake River. Given the community's sensitivity to
this controversial management action, a holistic comprehensive updated
evaluation seems prudent, and long overdue. The scope of future
evaluations need to more fully address the balance of benefits and risks
between anadromous and resident fish resources.
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