Independent Scientific Advisory Board

for the Northwest Power Planning Council

and the National Marine Fisheries Service

851 SW 6th Avenue, Suite 1100

Portland, Oregon 97204

ISAB@nwppc.org

Review of Giorgi et al. Report

“Mainstem Passage Strategies in the Columbia River 

System: Transportation, Spill, and Flow Augmentation”

Robert Bilby

Peter A. Bisson

Charles C. Coutant

Daniel Goodman

Robert Gramling 

Susan Hanna

Eric Loudenslager

Lyman McDonald

David Philipp

Brian Riddell

Richard Whitney, Ad Hoc Member

June 4

ISAB 2002-1
ISAB 2002-1 Review of Giorgi et al.

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ISAB Review of Giorgi et al. Report “Mainstem Passage Strategies in the Columbia 

River System: Transportation, Spill, and Flow Augmentation”

Contents:

Introduction................................................................................................................... 1

General Report Evaluation........................................................................................... 2

General Evaluation of Comments ................................................................................ 5

Conclusions.................................................................................................................... 7

Appendix: Key Findings and Conclusions of Giorgi et al. with ISAB Analysis of 

Disputes from Comments (Council Questions 2-4) ................................................... 10

I. Transportation......................................................................................................... 10

Overall Effect on Juvenile Spring/summer Chinook and steelhead:........................................10

Lower Monumental and McNary dams:.................................................................................11

Use of Trucks:.......................................................................................................................11

Fall Chinook: ........................................................................................................................12

Upper Columbia River: .........................................................................................................12

Statistical Foundation:...........................................................................................................12

“D”: ......................................................................................................................................12

Homing:................................................................................................................................14

Stress of Transportation:........................................................................................................14

Direct Mortality:.......................................................................................................... 15

II. Spill ......................................................................................................................... 15

Overall Synthesis: .................................................................................................................15

Project Spillway Passage Efficiency:.....................................................................................15

Survival in Spill at the Dam:..................................................................................................15

Survival Affected by Spill Volume at the Dam: .....................................................................16

Survival Estimated Over Several Dams, Empirical Studies ....................................................16

Survival Estimated Over Several Dams, Model Analyses: .....................................................17

Adult Passage Impacts:..........................................................................................................18

Uncertainties and Potential Sources of Dispute on Spill:........................................................18

Total Dissolved Gas:.................................................................................................... 19

III. Flow Augmentation .............................................................................................. 20

Introduction ..........................................................................................................................20

Premises for the Flow-Augmentation Strategy.......................................................................20

Speed of Outmigration of Juvenile Salmonids: ......................................................................20

Effects of Flow on Survival of Juvenile Salmonids:...............................................................21

Survival of Yearling Chinook................................................................................................21

Survival of Steelhead ............................................................................................................22

Survival of Snake River Fall Chinook Salmon.......................................................................22

General Flow Augmentation Evaluations...............................................................................23

Effects of Augmented Flow on Water Temperature Leading to Effects on Survival of Juvenile 

and Adult Salmon and Steelhead-..........................................................................................24

Model Studies .......................................................................................................................24

Uncertainties and Potential Sources of Dispute on Flow Augmentation .............................. 25

References Cited.......................................................................................................... 27

List of Comments........................................................................................................ 29
ISAB 2002-1 Review of Giorgi et al.

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ISAB Review of Giorgi et al. Report “Mainstem Passage Strategies in the Columbia 

River System: Transportation, Spill, and Flow Augmentation”

Introduction

The ISAB commends the Council for commissioning the summary report “Mainstem 

Passage Strategies in the Columbia River System: Transportation, Spill, and Flow 

Augmentation” by A. Giorgi, M. Miller, and J. Stevenson of BioAnalysts, Inc. (Giorgi et 

al. 2002). The Giorgi et al. report was created for the Council as a background document 

in the context of the mainstem program amendments. Council has periodically asked the 

ISAB and others to provide succinct “white papers” or “State of Science” reports that 

summarize the latest understanding about topics relevant to managing the fish and 

wildlife resources of the Columbia River basin in mitigation for the federal hydropower 

system. The Giorgi et al. report summarizes existing information on three topics that the 

ISAB and its predecessor advisory groups have debated intensely (and advised the 

Council about) over the past decade or so. 

The Council requested at its April 2002 meeting that the ISAB evaluate the report and the 

comments on it received from agencies and the public. The Council asked the ISAB to 

evaluate whether the Giorgi et al. report captures the full spectrum of scientific issues and 

knowledge related to mainstem passage, and specifically whether it adequately addresses 

the following questions:

1) What does the scientific literature tell us regarding the benefits, shortcomings, or risks 

associated with each passage strategy as compared to other passage options?

2) Which aspects of the scientific information are in dispute?

3) What are the critical uncertainties attending each strategy?

4) What is being, or could be done to reduce uncertainty and disputes?

In the context of the public comments, the Council asked how serious are the disputes 

raised in the public comments, and whether the various opinions are really very 

divergent.

The summary document by Giorgi et al. has helped update the ISAB’s understanding of 

the issues, and we are confident that it will be useful to the Council and Council staff. 

The comments help round out the outstanding issues. 

We offer the following thoughts as both technical critiques and indications of the 

implications for the Council and others that arise from the information in the report and 

the agency and public comments. General thoughts particularly relevant to question 1 are 

presented in the General Report Evaluation section of the text that follows. We also 

provide a general evaluation of the comments. 

Our more specific thoughts are assembled as an appendix. With respect to the second 

question, we felt it to be most helpful to list the key findings and conclusions of Giorgi et 

al. and to address questions 2, 3, and 4 together for each finding and conclusion. We have 

done this by briefly discussing the comments received for each finding and conclusion, 
ISAB 2002-1 Review of Giorgi et al.

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identifying where no comments were received, and discussing those findings and 

conclusions where disputes are identified. Where it seemed useful, we provide our own 

assessments. 

Mainstem issues are an important part of the Fish and Wildlife program (FWP), though 

their prominence has declined on the Council’s agenda, since the NMFS Biological 

Opinion has created other priorities. Earlier attention of FWP planning was directed 

largely toward enhancing salmon survival in the mainstem where the federal hydrosystem 

dominated the physical and operational environment, whereas recent focus has shifted 

toward tributary habitats and artificial production. Debates over the mainstem issues of 

transportation, spill, and flow motivated specification of measures in the published 

program documents that, while contentious, formed operational guidelines for the region. 

Hypothesized relationships between flow and fish survival were critical to the rationale 

for such guidelines, but the evidence for the respective hypotheses was not conclusive. 

The 1994 FWP (NPPC 1994) focused on alternative flow-survival hypotheses, with 

measures formulated to plan for specific tests of these hypotheses. The program called for 

analytical efforts through the PATH process (a multi-agency analysis group Planning and 

Analysis for Testing Hypotheses) and the design and implementation of field 

experiments. The efforts of PATH yielded valuable data syntheses but the anticipated 

major field studies to test alternative hypotheses to explain differences in fish survival at 

different flow regimes were never carried out. Unresolved questions about fish passage in 

the mainstem, especially the flow-survival relationship in relation to policies calling for 

flow augmentation, brings the mainstem to the Council’s attention once again. 

General Report Evaluation 

Giorgi, Miller, and Stevenson have done a good job of reviewing mainstem passage 

strategies designed to improve survival of juvenile salmonids in the Columbia River 

system. Their focus is on review of key studies and analyses that have taken place 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 (BO). Their approach was to abstract the key findings of the studies and 

compare the results. We believe they have largely succeeded in this task, and the 

resulting report provides information that ought to form the basis of revisions in the 

Council’s Fish and Wildlife Program, as well as guides for upcoming Mainstem and 

Systemwide project solicitations.

With respect to the ISAB’s advisory role for both the Council and the National Marine 

Fisheries Service, we emphasize that there are many uncertainties in the information used 

as a basis for the hydropower mitigation actions in the FWP and for the Reasonable and 

Prudent Alternatives (RPAs) of the Biological Opinion. A concerted effort is needed to 

reduce the uncertainties. The Giorgi et al. report helps all parties to focus on these 

uncertainties. 

The information reviewed by the Giorgi et al. report was summarized objectively. 

Findings and conclusions were specified where appropriate based on the scientific 
ISAB 2002-1 Review of Giorgi et al.

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information available. In cases where the results were open to question, these were 

identified as critical uncertainties and "research opportunities" (often a euphemism for 

badly needed information). These uncertainties and research opportunities provide a 

valuable basis for soliciting new work under the Fish and Wildlife Program. The report 

cites important scientific literature that should be the foundation for new proposals.

Overall, the report was very conservative in drawing statistical conclusions. This fact 

needs to be understood for proper interpretation of the implications of the report. From a 

purely statistical standpoint, tests that fail to show statistical significance in data can be 

definitive in stating that no effect was found, yet these tests do not definitively prove the 

absence of effect. 

The report’s statistical conservatism affects its value as a synthesis of current 

understanding. The report is not an “analysis” of the issues, but a compendium of 

findings to date. The ISAB considers this to be an important distinction. For example, 

when the report says no significant effect has been detected, this is technically a correct 

summary of the statistical analyses reported in the individual studies that were reviewed, 

but it should not be taken to preclude the possibility that an effect exists. The possibility 

remains that new studies or further rigorous analyses of existing data (in particular, 

analyses that combine data from several separate studies) would generate statistically 

significant results or a different answer. Future analyses should put more emphasis on 

statistical parameter estimation and power analysis, rather than just hypothesis testing.

A further limitation is that the Giorgi et al. report is narrow in the number of hypotheses 

that it reports (untested, but potentially valid, hypotheses were not discussed). There is 

much room for additional research, meta-analysis, and synthesis; the Council should not 

be misled by the apparent conclusiveness of many statements in the report. There are, for 

example, untested hypotheses related to flow that could significantly alter our view of the 

situation surrounding flow augmentation policies (discussed further in the appendix). 

Much recent work and ongoing studies related to different flow regimes and concurrent 

changes in other factors have not been fully analyzed. This is important work that still 

needs to be done.

We believe it was wise of Giorgi et al. to focus on the recent studies that were conducted 

under contemporary system operations. As they point out, there have been significant 

changes in river operations since the early 1990s, including improved bypass systems at 

the dams and other measures. In addition, there have been significant improvements in 

the ability of researchers to measure the effects of these changes on survival of 

salmonids. However, as several of those who provided comments on the report pointed 

out, it would perhaps have been useful for the authors to provide more commentary on 

studies conducted prior to the 1990s. Inclusion of the conclusions from the earlier studies 

would have been facilitated by reference to a number of documents that have synthesized 

results up to and into the 1990s such as the National Research Council report Upstream 

(NRC 1996); the Independent Scientific Group report Return to the River 2000 (ISG 

2000); a series of ISAB and PATH reports related to transportation, spill and flow (for 

ISAB see www.nwcouncil.org/library/isab); and Chapman et al. (1991, 1994, and 1995), 
ISAB 2002-1 Review of Giorgi et al.

4

as examples. We are not asserting that inclusion of the earlier studies would have 

forestalled any current or future disputes among the proponents of diverse management 

actions that have evolved within the Columbia Basin. However, the fact that for the most 

part the key conclusions of Giorgi et al. agree with the older studies ought to bolster the 

Council’s confidence in the Giorgi et al. review. We discuss this point further in the 

appendix.

A very useful contribution that may be extracted from the Giorgi et al. report is the 

identification of premises that have formed the foundation of the three mainstem

strategies for improving survival of juvenile salmonids as they migrate to the sea. These 

are:

1. Transportation. The premise is that transported fish will survive to returning adults at 

rates that will exceed rates of inriver migrants (p. 6).

2. Spill. The premise is that since spillways offer the safest passage route at the dams, 

provision of spill will improve total survival of smolts passing the dams. (While this 

premise is not specifically stated by Giorgi et al., it is implied in their discussion, 

particularly their Summary.) 

3. Flow Augmentation. There are two premises with flow augmentation:

a) Increased water velocity leads to increased migration speed, which leads to 

increased survival of juvenile salmonids.

b) Lowering summer water temperature with cool water from Dworshak Dam 

leads to improved migratory and rearing conditions for both juvenile and adult 

salmonids which results in improved survival. (p.60) 

The strength of the existing evidence for these premises may be evaluated from the 

Giorgi et al. report (in answer to the question asked by the Council “What does the 

scientific literature tell us regarding the benefits, shortcomings, or risks associated with 

each passage strategy, and as compared to other passage options?”). The evidence can be 

briefly summarized for each strategy in terms of the scientific information that has 

accumulated in support of each premise. Briefly, it may be said that the accumulated 

evidence supports the premises that:

1) transportation by barge from the Snake River increases the rate of return of adult 

spring/summer hatchery chinook and steelhead, particularly in years of low flow, 

2) provision of spill increases the survival rate of migrating juvenile salmonids,

3) flow augmentation designed to increase speed of migration does increase migration 

speed for most species, but evidence that this leads to increased survival is 

inconclusive because of the inability to separate numerous interrelated factors that 

affect survival at the same time, 

4) flow augmentation from Dworshak Dam in summer reduces Snake River 

temperatures, at least within Lower Granite reservoir. The available evidence 

indicates that temperature effects depend upon the volume of cold water inflow 

relative to total flow in the Snake River (greatest effect at low Snake River flows) and 
ISAB 2002-1 Review of Giorgi et al.

5

that effects of only 1-2 degrees are to be expected as far downstream as Ice Harbor 

Dam. No biological evidence for benefits to fish survival is available.

The Giorgi et al. summary and the ISAB evaluation of the broader mainstem situation 

both highlight that a set of well-designed, manipulative, field experiments is needed, 

particularly for the issue of flow and smolt survival. The low flows of 2001 with the 

correspondingly low in-river smolt survival for some species and life-history types 

suggest that, at the extreme, survival of some types of fish is affected by low flows 

(and/or the numerous other factors that occur in association with it, such as high 

temperature, low turbidity, slower velocities, less inundation of riparian zones, more 

frequent and rapid changes in flows in response to load following, and others not yet 

identified). These experiments must go beyond analysis of existing monitoring data, and 

include specific hypothesis-testing manipulations. Such experiments are admittedly 

difficult to conduct. However, experimental designs can make use of extreme conditions 

when they occur naturally (as in 2001) and some experimental conditions can be created 

within bounds of water availability and operational constraints. The ISAB can suggest 

such experimental designs in another forum. 

General Evaluation of Comments 

The comments from the public and agencies provided additional useful technical 

information, usually amplifying points made in the Giorgi et al. report, but often, it is our 

impression, from more of an advocacy position for certain management strategies. 

Contrary to what was suggested in some of the comments, we did not see any pervasive 

tendency for selective use of data or misinterpretation of results by authors of the Giorgi 

et al. report. Genuine technical disagreements occur over possible interpretations of 

available information for methods of analysis and implementation measures. Giorgi et al. 

were criticized for not providing the full range of scientific “opinion” on the key issues, 

yet the intent of the report was to summarize information, not opinion. However, as we 

noted ourselves above, the report does not summarize alternative hypotheses that have 

not yet been tested. To the extent that the commentors were seeking more attention to 

these alternative hypotheses, we concur. The comments can be used, along with the 

report, to frame the uncertainties and opportunities for additional research.

Several of those who provided comments on the Giorgi et al. report were critical of the 

fact that the report, as it reviews the passage strategies, deals with an “incremental 

approach” designed to improve survival of juvenile salmonids at various points as they 

transit the mainstem. For example, there appears to be universal agreement that spill 

offers the safest passage route for juvenile salmonids at most projects (The Dalles Dam 

may present an exception, under some levels of spill), and that any improvement in 

survival provides an increment of benefit at that project. But two issues are raised by the 

critics, one a question whether benefits of spill can be measured in the system as a whole, 

and the other a question whether even at best, these improvements in survival are likely 

to be sufficient to lead to recovery of the endangered stocks of salmonids in the Columbia 

Basin, and in particular, the Snake River stocks of endangered anadromous fish. 
ISAB 2002-1 Review of Giorgi et al.

6

There are two responses to the criticism on these points, the first is that Giorgi et al. were 

responding to the assignment they were given (to summarize current information, and not 

to make policy judgments), and the second is that the information summary is meaningful 

as it stands because of the management predicament in which we all find ourselves. The 

predicament is that no measure(s) has (have) been identified that will do more than 

provide incremental increases in survival of salmon in the basin. Perhaps one exception 

would be the restoration of salmon in areas where they have been extirpated by blockages 

to their passage. Other than that, salmon populations have been reduced by an 

accumulation of increments over a long time period, and the incremental-improvement 

approach is being used out of necessity by the Council and NMFS to move toward 

recovery. The approach proceeds on the premise that an incremental improvement in one 

location will be passed on as a benefit to the next location, accumulating thereby into the 

potential for a large effect in the system. NMFS’ analysis using the CRI modeling effort 

led to the conclusion that the primary opportunities for major improvements in survival 

now lie in tributary and estuarine habitat improvement rather than in the mainstem.

However, the Giorgi et al. report suggests that there are still improvements to be made in 

the mainstem, an opinion that most commentors and the ISAB share. 

Some comments, particularly those of NMFS, corrected some misstatements in the 

Giorgi et al. review. Also, the comments indicated a number of details that could have 

stood further elaboration. Materials not available to Giorgi et al. were suggested for 

further analysis. These comments, while useful, did not seem to the ISAB to require 

major changes in either the Giorgi et al. review or our views of it. 

Another common theme in some comments was the belief that release of water from 

reservoirs far upstream in the basin for flow augmentation provide little benefit to 

downstream migrants yet can have measurably detrimental effects locally in both 

tailwaters and reservoirs. This was emphasized especially for the reservoirs in Montana 

that drain through a long chain of rivers, lakes, and reservoirs before the water reaches 

the migrant corridor in the lower river. The tradeoffs between headwater and downstream 

effects have been an important part of the flow augmentation debate for some time. The 

Giorgi et al. report touches on this issue under the heading “Benefits and Risks to other 

species” (p.78), where the ISG 1996 report is quoted. The commentors have a valid point 

that deserves further definition of biological effects and risk-benefit analysis. The 

analyses by Council’s Montana staff (several years ago) and the Idaho Department of 

Water Resources’ more recent reanalysis of NMFS’ smolt travel time and survival data 

for the Snake River (Dreher et al. 2000) and the ISAB review of it (ISAB 2001), along 

with other unpublished analyses cited in the comments suggest that this topic deserves 

more technical evaluation and better designed experimental studies that might provide 

more conclusive data. Giorgi et al. conclude that “Comprehensive flow augmentation 

evaluations are generally lacking, only a handful of studies have attempted to quantify the 

volume and shape of water provided as FA [flow augmentation], and translate that 

incremental increase in flows to changes in water velocity and temperature [and thence 

into changes in smolt travel time and survival].” “The scope of future evaluations needs 

to more fully address the balance of benefits and risks between anadromous and resident 

fish resources.” And we might add, other water uses. 
ISAB 2002-1 Review of Giorgi et al.

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Conclusions

It is clear from both the Giorgi et al. report and the comments that the mainstem 

management issues tackled by the report (transportation, spill, and flow augmentation) 

are not yet resolved, although there is little or no dispute on many component topics (see 

appendix). Lack of resolution is largely due to a lack of critical information; further 

resolution requires additional research, experimental manipulation, adaptive 

management, monitoring, and analysis (evaluation).

For additional conclusions, we return to the questions asked of us by the Council. On the 

whole, the report does capture most of the full spectrum of scientific issues and 

knowledge related to the three designated strategies on mainstem passage (transportation, 

spill, flow augmentation) as reflected in published reports. However, we found some 

important omissions. For example, Giorgi et al. do not present an adequate discussion of 

the portion of the flow augmentation strategy that calls for flows out of the upper 

Columbia River storage reservoirs, particularly with respect to its effects in the lower 

river. Some recent literature contained in Connor et al. (2001) on effects of summer flow 

augmentation and other factors on survival of smolts in the Snake River was not 

reviewed. The issue of mainstem habitat and its effects on healthy smolts (i.e., treating 

the mainstem as a habitat for feeding, growth, and other life functions during rearing and 

migration) was not treated (discussion of this topic was a major part of the ISG’s Return 

to the River 2000 science review). This and additional, alternative explanations for the 

clear degradation in smolt survival at low river flows were not pursued. Although we 

recognize that this was not the intent of the Giorgi et al. report, we suggest that the single 

premise offered by Giorgi et al., with respect to effects of volume of flow, i.e. that 

volume of flow affects travel time which in turn affects survival, while it accurately 

reflects much of the current thinking in the basin, is not the only possible explanation for 

low survival at low flow. We offer more on this subject in the Appendix. 

We evaluated whether the report adequately addresses the following questions:

1) What does the scientific literature tell us regarding the benefits, shortcomings, or 

risks associated with each passage strategy, and as compared to other passage 

options?

The report is not an assessment of management options in the literal sense of this 

question, but a summary of the latest technical and scientific information that is 

appropriate to such management evaluations. It is a guide to technical uncertainties and 

needed information, and in that role it provides guidance for needed work on the 

mainstem. Some of that work could be funded through the Mainstem/Systemwide 

solicitation for the Council’s Fish and Wildlife Program. Evaluation of policies to 

balance or tradeoff among management benefits and risks was not an obvious part of this 

study. Clearly, the scientific literature, as represented fairly by the Giorgi et al. report is 

not sufficient in and of itself to resolve the issues. Focused large-scale experiments, 

monitoring of management actions, and analyses are needed.
ISAB 2002-1 Review of Giorgi et al.

8

The premises of transportation (for some species and life-history types) and spill are well 

supported by the available evidence. The evidence available in support of the premises 

that form the foundation for the flow augmentation strategies are inconclusive. These are 

the weakest of the foundations for the three strategies, and are the most disputed. It is 

time to think in terms of new premises that might explain the data, or to design specific 

experiments to isolate the effects of factors that are interrelated with flow. This is 

discussed further below and in the Appendix.

2) Which aspects of the scientific information are in dispute?

The report adequately identifies most of the problem areas. The comments highlight 

some of these aspects and add a few more. We have identified these in the appendix. 

They are:

• Transportation: A question whether all adults are accounted for, issues of “D” 

and its related factors (e.g., “extra mortality”), changes in homing, relative 

efficacy of trucking and barging;

• Spill: General applicability of results from The Dalles Dam (whether more 

spill is always better for fish), use of models to evaluate systemwide benefits 

of spill, conclusiveness of empirical studies considering all confounding 

factors;

• Flow: Applicability of migration speed (travel time) to estimating survival, 

appropriate reach lengths for estimating survival (per project vs. per mile), 

species specificity of flow-survival relationships, whether inability to tease out 

exact causes (among co-varying temperature, flow, date, turbidity, etc.) should 

negate the overall relationship of survival to flow especially in fall chinook, 

suitability of year-to-year comparisons of survival vs. flow considering other 

dissimilarities among years, importance of small temperature differences in 

the river near fish physiological limits, importance of food web issues, 

relationships between flow rate and delayed survival effects related to 

migration delay (extra mortality), value of models vs. empirical data.

3) What are the critical uncertainties attending each strategy?

The Giorgi et al. report specifically concludes each section with a list of critical 

uncertainties. We have amplified on these in the appendix. The critical uncertainties are 

essentially the same as the list of issues in dispute, listed above. There are more 

uncertainties for flow augmentation than for the other mainstem topics. For flow, we 

would add the general uncertainty associated with failure to explicitly state and test 

alternative hypotheses that could offer more promise for resolving the issue than have the 

debates over current hypotheses. 

4) What is being, or could be done to reduce uncertainty and disputes?

The report specifically concludes each section with a list of “research opportunities” 

(needed work). Again, more work is needed to resolve issues of flow than for other 

issues. The ISAB believes that the list of work required to resolve flow issues needs to be 

expanded to include hypotheses or premises not treated by Giorgi et al. These hypotheses 

were not treated because the necessary experiments, monitoring, or analyses have not 

been done. These hypotheses would encompass the fuller range of scientific opinions 
ISAB 2002-1 Review of Giorgi et al.

9

sought by commentors. The ISAB goes further and recommends that both further 

analysis of existing data and the design of new experiments be given high priority. The 

ISG (ISG 2000) suggested two premises with respect to effects of flow on survival of 

juvenile salmonids that they felt merited further study. One, that large and rapid 

fluctuations in flow, associated with load following might reduce the productive capacity 

of the near shore zone used by incubating and migrating juvenile salmonids, and two that 

these rapid fluctuations could lead to stranding of redds and juveniles, such as has been 

observed in the Hanford Reach. Load following is particularly evident at times when 

average river flows are low, and might be another factor involved in low survival 

observed at low flows.

Testing of existing and new hypotheses for the effects of flow on survival and the 

efficacy of flow augmentation are especially needed. Rather than reacting passively to 

proposals submitted for research in this area (e.g., through the Mainstem/Systemwide 

solicitation), the ISAB recommends that the Council return to the strategy outlined in the 

1994 Fish and Wildlife Program, which called for explicit statement and testing of 

hypotheses with the aim of resolving the scientific aspects of these issues (recognizing 

that there will always be policy issues that go beyond science). The ISAB recommends 

that the Council, with advice from NMFS, specifically solicit proposals that clearly state 

existing and novel hypotheses for the effects of flow on smolt survival and provide 

experimental designs for testing them. The report by Giorgi et al. provides a good start 

for the existing hypotheses, but innovative thinking beyond this report is needed for other 

hypotheses. 
ISAB 2002-1 Review of Giorgi et al.

10

Appendix

Key Findings and Conclusions of Giorgi et al.

with ISAB Analysis of Disputes from Comments

(Council Questions 2-4)

In this appendix we list and discuss the key findings and conclusions of Giorgi et al., 

discuss the main points raised in comments received by the Council during the public 

comment period, and where necessary or desirable provide our analysis of the findings 

and conclusions in the context of the comments. The mainstem strategies Giorgi et al. 

were asked to review are: I. Transportation, II. Spill, and III. Flow Augmentation. For 

reference to the Giorgi et al. report, we have noted the page(s) where the conclusions can 

be found. 

I. Transportation 

Giorgi et al. conclusion regarding Overall Effect on Juvenile Spring/summer Chinook 

and steelhead: 

Barge transportation of hatchery-reared juvenile spring/summer chinook and steelhead 

collected from Lower Granite and Little Goose dams on the Snake River leads in most 

years to higher rates of return to the river of adult fish than allowing the fish to transit the 

river using the passage routes available at the dams. For steelhead, in general the results 

are more variable than for chinook salmon. Therefore it is difficult to conclude that either 

transport or inriver passage is more favorable for steelhead. Effects on wild fish are not 

clear because of small sample sizes. (page 25)

Comments: There is little or no room for dispute of these facts for hatchery

spring/summer chinook (with the possible exception of fish from the Dworshak 

Hatchery, according to the Joint Technical Staff Memorandum). The situation for 

steelhead is less clear. According to Giorgi et al., the steelhead sample is very 

small. Only one study had a confidence interval applied to the transported vs. inriver ratio (TIR) estimate, and it was near 1.0. Similar findings were reported in 

syntheses by NRC (1996) and ISG (2000). The ISG (ISG 2000) found that in 

cases where sufficient numbers of adult recoveries were made to make a judgment 

possible, transportation increased (to varying degrees) the survival of yearling 

hatchery spring chinook to the point of release in 26 out of 36 studies (i.e. 

Transported/In-river was greater than 1) over the years from 1968 to 1995. In four 

of the remaining studies, T/I [TIR of Giorgi et al.] was equal to 1, while only six 

were less than 1. Save Our Salmon (SOS) comments that their concerns with the 

report have to do with conclusions drawn and management actions that should be 

taken as a result, rather than to the data analysis (p. 10). A dispute arises over 

whether there might be a loss of adults that end up not being counted. Two issues 

raised have to do with 1) measurement of a factor labeled delayed differential 

effects, D, and 2) possible effects of transportation on homing. The D factor is 

discussed below. If transportation affects homing ability then the broader return 
ISAB 2002-1 Review of Giorgi et al.

11

rate of adults would be even higher than measured to point of release, whether the 

return rate of hatchery strays is a liability or an asset is itself a matter of debate. 

The concern raised is the possibility of effects on salmon or steelhead stocks in 

the streams where the strays may appear. Giorgi et al. acknowledge this as an 

uncertainty and recommend studies. This is discussed further below.

Giorgi et al. conclusion regarding Lower Monumental and McNary dams: 

No clear benefit has been shown for transportation of smolts of spring/summer chinook 

and steelhead stocks from Lower Monumental or McNary dams. (pages 13, 26)

Comments: Save Our Salmon and the Joint Technical Memorandum agree with 

this finding. Save Our Salmon recommends that collection of juvenile salmonids 

at Lower Monumental and McNary dams for transportation should be 

discontinued. The data for the mid-Columbia stocks at McNary are less 

convincing, and more study there might be warranted. However, the premise on 

which a study would be based is unclear. The fact that benefits from 

transportation decrease as one goes downstream should not be surprising. 

Transportation can only offset the inriver mortality incurred if smolts are left in 

the river from that point. Smolts transported from Lower Granite and Little Goose 

dams are avoiding 6 or 7 dams and associated reservoirs, whereas those 

transported from Lower Monumental avoid 5 dams and those from McNary avoid 

only 3. Based on present evidence, the ISAB concurs with the conclusion of 

Giorgi et al., and supports re-evaluation of these transportation sites. 

Giorgi et al. conclusion regarding Use of Trucks: 

Trucks are used in place of barges at the beginning and ends of the outmigration when 

fish are not abundant enough in the collection systems to justify the use of barges. (page 

2)

Comments: There were no public comments on this point. However, while this is 

a description of methods and not a research result as presented by Giorgi et al., it 

is a point that merits discussion. The ISG (2000) found that return rates of 

spring/summer chinook and steelhead transported by truck were lower than of fish 

that transited the river. However, the studies of trucking and barging were done at 

different times and used different methods, and it is possible that the observed 

lower survival in truck transportation was due to poorer procedures in early 

efforts. It would seem to be advisable to discontinue transportation early in the 

spring when fish are not abundant enough to justify transportation by barge, at 

least until a new experimental test of truck transportation, using better procedures, 

resolves the question. Differences in the efficacy of transportation by trucks and 

barges late in the spring and in the summer are less clear, especially for fall 

chinook and other anadromous species that have not been studied extensively. 

The ISAB supports further study of the relative efficacy of trucking and barging, 

using common study protocols and a variety of stocks and migration times. 
ISAB 2002-1 Review of Giorgi et al.

12

Giorgi et al. conclusion regarding Fall Chinook: 

The benefit of transportation of fall chinook is an unknown. No mass transportation study 

of fall chinook has been conducted. Studies using hatchery fall chinook are being 

planned. Continued research on these important issues is warranted. (page 25)

Comments: There were no comments on this subject. The ISAB points out that 

uncertainties continue to exist on whether transportation of a high percentage of 

all anadromous fish will maintain high diversity of life history types of all species 

of salmon and steelhead in all seasons. The ISAB concurs that study is needed. 

Giorgi et al. conclusion regarding Upper Columbia River: 

Stocks of chinook, steelhead, and sockeye from the upper Columbia River above Priest 

Rapids Dam have in some years been intercepted at McNary Dam for transportation to 

below Bonneville Dam. Under current operating strategies in the BO, interception at 

McNary Dam is de-emphasized in favor of spill as a passage alternative. There have been 

no studies since the 1980s. Study designs are being formulated for 2002. (pages 26, 27)

Comments: There were no comments on this point. The ISAB concurs that more 

information might be useful, but sees no particular urgency (see comment above). 

Giorgi et al. conclusion regarding Statistical Foundation: 

There are weak statistical foundations for many study conclusions. Rarely have authors 

specified levels of statistical accuracy and precision of estimates or significance levels 

between or among estimates. Many of the annual SAR (smolt-to-adult returns), TIR 

transported to in-river ratios), and D (delayed differential effects; see below) estimates 

have such poor precision that their usefulness may be questioned. (page 27)

Comments: There were no direct comments on this subject, although it comes into 

play in evaluation of many studies and specifically in relation to the next finding. 

The ISAB concurs that a better statistical foundation is desirable. This means, first 

of all, that more thorough statistical evaluation of data should be expected from 

all individual studies (particularly with respect to putting confidence intervals on 

parameter estimates); second, this means that meta-analyses combining data from 

multiple studies are warranted; and third, this means that future research should 

consider large scale experiments with designs based on statistical analysis of 

existing data to ensure that the new experiments are more conclusive. 

Giorgi et al. conclusion regarding “D”: 

The concept of Delayed Differential Effects, i.e. “D”, is confusing. Given the poor 

precision of estimators of D and indirect methods to estimate D, there is no opportunity 

for sound statistically based inferences with existing data. As a consequence, some may 

view D to be a confusing and rather abstract parameter that has little intuitive relevance. 

Furthermore, it appears that except for some modeling applications, D can provide little 

more information to the manager than prevailing TIR estimates that are used to derive D 

in the first place. (page 19)
ISAB 2002-1 Review of Giorgi et al.

13

Comments: WDFW agrees that studies are needed to elucidate the variety of 

parameters included in the parameter D (See below). Save Our Salmon feels that 

Giorgi et al. downplayed the importance of D and refers to a paper by Bouwes et 

al. (2002) in which the authors are said to find that mortality of smolts after 

release from the barges is nearly twice as high as in-river migrants. Giorgi et al. 

acknowledged that finding, but concluded that even with this loss, the adult return 

rate of transported smolts is higher than in-river migrants. The Joint Technical 

Staff Memorandum pointed out that Giorgi et al. did not discuss the issue of 

possible “extra mortality” of in-river migrants due to the hydroelectric system, 

although NMFS BO RPA actions were developed to address the issue. The ISAB 

has commented on this issue previously and concurs that the concepts are 

confusing and not always helpful. 

Both D and "extra mortality" are terms specific to a particular set of models that 

were analyzed by the PATH project. During the course of PATH, both D and 

"extra mortality" were estimated in indirect ways, for lack of direct data. Since 

then, the debate persists, because adequate data have never been collected. In the 

time since the PATH era, more data have accumulated, there have been 

improvements in the bypass facility at Bonneville, the PIT tag reading facility at 

John Day has become operational, and there is some PIT tag collection below 

Bonneville, but we still do not have adequate sample sizes for estimation of inriver survival rates to below Bonneville. 

The debate has perhaps been exacerbated because of drift in what various parties 

mean when they refer to D or "extra mortality." These hypothetical differential 

rates, D and extra mortality, are used by proponents of both sides of the argument 

over the efficacy of transportation, depending upon their belief systems. There is, 

indeed, evidence in the literature for latent or delayed mortality of fish from nonlethal stresses (at the time of exposure) that might be occurring in the Columbia 

River, and that might differ between transported and inriver groups. But these 

latent and delayed mortality measurements are not measurements of differential 

mortality between transported and in-river fish, as measured in the rates of adult 

returns to the river. The factors D and extra mortality were proposed only for the 

comparative survival of returning adults. The factors D and "extra mortality" as 

used in PATH were largely placeholders for mortality components, or mortality 

relationships, that could be real and could be important, if we could define them 

unambiguously and collect the proper data to estimate them with sufficient 

resolution. 

Giorgi et al. correctly quote from the literature that D can be computed directly 

from the T/I ratios and independent estimates of inriver survival to below 

Bonneville Dam. While the controversy over D probably is not that important in 

the grand scheme of things, there are still legitimate questions about survival of 

inriver fish in the John Day pool, survival at the newly enhanced Bonneville 

structures, and, futhermore, growing interest in survival rates in the estuary of 

both transported and inriver fish that might be well-served by an ambitious 
ISAB 2002-1 Review of Giorgi et al.

14

survival study design with a focus that begins well above Bonneville and reaches 

the ocean plume.

 The ISAB concludes that issues associated with “D” and “extra mortality” are not 

likely to be resolved until studies are undertaken specifically to detect and 

measure them. 

Giorgi et al. conclusion regarding Homing: 

Homing of adult salmon is likely to be affected by transportation. There have been 

studies, limited in scope, that indicate transportation can impair homing particularly for 

steelhead, sockeye, and fall chinook. A more systematic and comprehensive evaluation of 

the effects of the mass transportation strategy on homing ability is warranted. One study 

is being planned. Impaired homing would show itself as a lower return rate of transported 

fish than expected, which might pose no problem for the transported stock, but some 

investigators raise the prospect of possible effects on the stock in the recipient stream(s). 

(pages 23, 25)

Comments: There is general agreement on this point. We concur.

Giorgi et al. conclusion regarding Stress of Transportation: 

Stress effects on transported fish are poorly identified. It is difficult to determine, on the 

basis of available information, whether stress associated with the collection and 

transportation of juvenile salmon contributes to mortality. Another way of saying it is that 

there has been no demonstration of an effect on survival. (pages 21, 22)

Comments: The NMFS commented that not all bypass facilities are created equal 

and that some collection facilities may be contributing to juvenile fish mortality. 

We concur. There were no other comments on this point. However, the ISAB 

reiterates a point made in many of its and its predecessor groups’ previous 

reviews of transportation, which is the importance of life-history diversity in 

evaluating the efficacy of transportation. Every aspect of transportation, including 

susceptibility of collection, direct mortality, overall stress during collection and 

transport, and long-term survival may differ among species and life stages. 

Transportation may be exerting a selective effect among existing stocks that is not 

desirable for long-term sustainability. We concur with Giorgi et al. that this topic 

is poorly identified. In years with normal or high flows and better than average inriver survival, it may be better for the fish community to minimize transportation. 

We reiterate that failure to demonstrate an effect does not prove that there is no 

effect, most especially if the available data are weak and the available studies 

have indifferent designs. 
ISAB 2002-1 Review of Giorgi et al.

15

Giorgi et al. conclusion regarding Direct Mortality: 

Direct mortality in the barges or trucks seems slight. There are no rigorous estimates of 

this source of mortality. Observers have seen few dead fish upon release. Exceptions are 

a couple of occasions when barges full of fish sank in the river. 

Comments: There were no comments on this point other than the NMFS comment 

noted above. See ISAB comment above. 

II. Spill

Giorgi et al. conclusion regarding Overall Synthesis: 

Routing smolts through spillways is generally considered to be the safest passage strategy 

at Columbia River and Snake River dams. (pages 36-53)

Comments: There was general agreement on this point, although NMFS pointed 

out that we do not fully understand the mechanisms associated with survival 

benefits of spill. We concur on both counts. We add that an additional benefit of 

spill, not mentioned in the Giorgi et al. report or in comments, is that spill 

accelerates passage “through the concrete.” Passage via spill is more rapid than 

passage through the powerhouse with its delays in the forebay and bypass system. 

Fish appear to be reluctant to enter turbine intakes, especially in the day, yet move 

rapidly in spilled water. Over the course of passing several dams, the timesavings 

could be substantial. 

Giorgi et al. conclusion regarding Project Spillway Passage Efficiency: 

Spillway passage efficiency varies among fish stocks, varies between day and night, 

varies with the percentage of river flow passing in spill, varies depending upon the 

method of measurement, and is project specific. Selecting an appropriate value to be used 

in predictions required to implement spill as a strategy will involve intense inspection and 

evaluation. (page 34)

Comments: There was no dispute on this point. It confirms findings of Whitney et 

al. (1997) in Council Document 97-15. The NMFS comment clarified definitions, 

although the intent of the Giorgi et al. conclusion seems clear. The ISAB concurs. 

Giorgi et al. conclusion regarding Survival in Spill at the Dam:

Numerous studies have shown that survival of juvenile salmonids passed through 

spillbays or sluiceways is higher than juveniles passed through the turbine intake bypass 

systems or turbines at particular dams. Flow deflectors that are in place at some dams to 

reduce total dissolved gas in solution may reduce survival by 1-3%, depending on the 

dam and species, but survival still exceeds that in turbine passage. (pages 36-38)

Comments: NMFS commented that many of the conclusions were drawn from 

summary data without reference to error bounds, which could alter results. Also 

there is a need to balance the additional mortalities from flow deflectors with the 

survival benefits from lowered total dissolved gas. There were no other comments 
ISAB 2002-1 Review of Giorgi et al.

16

on these particular points. The ISAB concurs with the need for error bounds and 

with the need for assessment of overall survival effects, yet also agrees with the 

general conclusion of Giorgi et al. 

Giorgi et al. conclusion regarding Survival Affected by Spill Volume at the Dam:

Collectively, there is some indication that smolt survival varies with discharge at some 

dams and in some cases, and that passage benefits may be associated with maintaining 

spill at moderate, rather than highest, levels. At The Dalles Dam, survival of juvenile 

salmonids in spill declined steadily, by an estimated 7%, as spill fractions rose from 30% 

to 64%, relative to the total volume of river flow. There is a strong indication that 

survival in spillway passage could be maximized by selecting the most benign level of 

spill. (pages 39, 53)

Comments: The results of the study at The Dalles Dam are a subject of dispute. 

Save Our Salmon comments that it is probably inappropriate to extend the results 

at The Dalles to other projects, because, the same phenomenon was not observed 

at Wanapum, Rock Island, and Little Goose dams, judging by the figures shown 

in Giorgi et al. They also raise a point about possible flaws in the study at The 

Dalles. WDFW also observes that this might be a site-specific phenomenon. The 

Joint Technical Staff Memorandum also raised a point relating to technical and 

analytical flaws in the study at The Dalles. We agree that it is inappropriate to 

extend the results of spill studies from one project to others without site-specific 

verification. The ISAB specifically made this point in its review of spill studies at 

The Dalles (ISAB 2000-1). However, the ISAB concurs with the point made by 

Giorgi et al. that the most benign spill level for a site needs to be determined, 

rather than assuming that more spill is always better. 

Giorgi et al. conclusion regarding Survival Estimated Over Several Dams, Empirical 

Studies

There have been few studies that attempted to develop estimates of systemwide smolt 

survival attributable to spill. There are conflicting results. The Muir et al. studies (cited in 

Giorgi et al.) suggest that survival was highest in years when spill levels were highest. On

the other hand, Zabel et al. (2001) pointed out that in the time-series they examined, the 

improved survival associated with a period of spill was time related, and occurred at a 

similar time in past years, regardless of spill. NMFS concluded that the results of this 

analysis were inconclusive. Giorgi et al. conclude that it is not possible to isolate spill as 

a discrete treatment in this kind of analysis, because too many variables affect survival. 

(pages 11, 12)

Comments: There is agreement on this issue in the Joint Technical Staff 

Memorandum. The Memorandum indicates that Giorgi et al. should have 

referenced the comments by the region’s fishery agencies and tribes on the severe 

limitations of this particular application, and provides a website where those 

comments are available. Save Our Salmon states that care should be taken not to 

conclude from the NMFS studies that spill was not effective in improving 

survival. The ISAB concurs there has been difficulty in isolating spill effects 
ISAB 2002-1 Review of Giorgi et al.

17

beyond an individual project and suggests that additional research should focus on 

identifying reasons why it has not been possible in some cases to measure 

systemwide improvements in survival attributable to spill, even though benefits at 

individual projects have been demonstrated. Faster passage through the concrete, 

noted in the general spill conclusion above, needs to be factored into an overall 

analysis. 

Giorgi et al. conclusion regarding Survival Estimated Over Several Dams, Model 

Analyses:

Giorgi et al. suggest employment of mathematical models, namely computer based 

models such as CRiSP or SIMPAS to estimate or predict the total mortality experienced 

by smolts in passing either a series of projects or a single dam. They attempt to identify 

key issues applying to the use of passage models in spill analysis. They identify a primary 

concern as being the criteria adopted for selecting the best estimate from a pool of 

estimates of spill efficiency and survival in spill, among other inputs that will be 

employed in the model analysis. “There will surely be factions that take exception to the 

resultant set of estimates.” It seems more appropriate for a diverse technical group to 

develop and apply criteria that would be used for assembling the most representative set 

of inputs that could be applied as a standard. It is not clear that NMFS employment of the 

SIMPAS model to evaluate changes in expected smolt survival under four spill scenarios 

accurately depicted spill related survival, particularly under the extreme low flow 

conditions experienced in 2001. The only analysis they found that attempts to assess the 

change in survival for the smolt population subjected to different spill scenarios is the 

2001 model analysis conducted by NPPC staff. It may not be totally satisfactory because 

the SIMPAS model used in the analysis probably needs updating. A number of improved 

estimates have become available since SIMPAS was constructed. Giorgi et al. doubt that 

it would be practical to attempt to design manipulative experiments that could isolate 

spill effects in the complex Columbia River system. (pages 47, 48, 55)

Comments: There is general agreement with the Giorgi et al. finding. Save Our 

Salmon agrees with Giorgi et al. in their reluctance to endorse the manner in 

which the NPPC applied the SIMPAS model to endorse maximized transportation 

and reduced spill as a passage strategy in 2001. ODFW comment that Giorgi et al. 

should have observed that the weight of evidence, including model analyses by 

the Fish Passage Center and NMFS, indicates that spill is beneficial on a 

population level. The Joint Technical Staff Memorandum states that there are 

severe limitations in the modeling approach. 

The ISAB finds that the SIMPAS model is being used in the region for several 

kinds of applications, some of which are inappropriate or questionable. This 

model can be an important and useful tool but it should be the subject of an 

update and verification, as suggested by Giorgi et al. In particular, input values for 

the SIMPAS model are most often ad hoc guesses and suffer from a lack of real 

measured data. It is important to build regular updates of the necessary parameter 

values into an ongoing long term monitoring and evaluation plan. As above, the 
ISAB 2002-1 Review of Giorgi et al.

18

effects of speed in passing smolts through the concrete when water is spilled 

should be factored into modeling.

In general, the ISAB warns against using models in attempts to "compensate" for 

the absence of critical data. This strategy cannot work satisfactorily for the long 

term. Without important data, analyses often deteriorate into unproductive 

conflicts between the backers of competing models that differ because of different 

assumptions. One proper use of models, when data are inadequate, is to identify 

which data would be most important to resolving the question, and to determine 

what would be the most efficient design for obtaining those data. 

Giorgi et al. conclusion regarding Adult Passage Impacts:

Observations in the field have suggested that spilling water can alter migratory patterns 

of adult salmon and steelhead, leading to protracted migration times. The relationship 

between fallback and spill discharge appears to be dependent upon the year and particular 

dam. Giorgi et al. conclude that there is some evidence that high spill levels may 

exacerbate delay and fallback, but were unable to find a study that specifically and 

explicitly evaluates the effects of the spill program on adult passage. 

Comments: There were no comments on this issue. The ISAB concurs. 

Giorgi et al. conclusions regarding Uncertainties and Potential Sources of Dispute on 

Spill: 

(1) In spill modeling exercises, values for model parameters should be periodically 

updated for each dam and species (stock). With notable exceptions, the data are not being 

systematically compiled and synthesized on a regular basis. 

(2) Modeling may be the only practical means to evaluate the probable relative 

effectiveness of various river-wide spill scenarios. Decisions on which parameter values 

should be entered into the models require a consensus approach by knowledgeable 

technical personnel.

(3) Results from empirical evaluations of river-wide spill effects are not conclusive 

because spill effects are not clearly isolated from other effects. Giorgi et al. do not 

believe that it is practical to conduct well-designed manipulative (controlled) experiments 

that could isolate spill effects as a causative factor, due to the complex nature of the river 

system and its operations. 

(4) Effects of spill on adult passage and survival to spawning should be established as a 

long-term monitoring program. 

Comments: WDFW commented that a very useful part of the Giorgi et al. 

document was the identification of critical uncertainties in the effectiveness of 

transportation, spill, and flow augmentation on increasing survival of juvenile 

anadromous salmonids during their outmigration. Save Our Salmon provided a 

cautionary note to the effect that many of the research needs identified relate to 

management actions that produce rather small impacts. 
ISAB 2002-1 Review of Giorgi et al.

19

The ISAB agrees with item 1, that parameters need to be updated regularly, both 

to account for possible changes in the system, and to capitalize on the growing 

mass of data. The ISAB disagrees emphatically with the implication in item 2 that 

modeling is a solution for the problem of inadequate data (see earlier comment on 

use of models). The ISAB observes that, with respect to item 3, it should be 

clarified that Giorgi et al. are apparently referring to a systemwide experiment to 

measure effects of spill on survival. We share their pessimism about persuading 

the power system operators to make an investment in dramatically manipulating 

the entire system. On the other hand, there have been a number of examples of 

manipulations at individual projects that were experiments designed to develop 

spill effectiveness relationships. Current approaches to studying this question 

depend upon natural or programmatic interannual variability in systemwide spill 

and an after-the-fact analysis, which leaves open a question about interannual 

variation in survival that might be independent of spill. 

We recommend more attention to deliberate experimentation on individual 

projects, perhaps one at a time, and perhaps rotating among projects, so as to 

obtain defensible estimates eventually for every project. We also recommend 

capitalizing on interannual changes in available water to provide systemwide 

variation (by having contingency plans in an experimental design to respond to 

water budget events as they occur). The design for monitoring the experiment at 

any given dam obviously must provide for following the fish for long enough to 

account for any delayed effects, to ensure that when the parameters are put into an 

eventual comprehensive model, the whole really will be represented by the sum of 

its parts. With respect to item 4, we have our doubts about the ability of passive 

monitoring to resolve the question, and for that reason we recommend 

experimentation in conjunction with monitoring.

Giorgi et al. conclusion regarding Total Dissolved Gas:

The biological monitoring program has demonstrated that compliance with the TDG 

limits outlined in the 1995 BO typically results in less than 1% of the juvenile migrants 

that are sampled exhibiting signs of gas bubble trauma. In contrast, conditions producing 

involuntary spill (i.e. when river flow exceeds powerhouse capacity) have resulted in 

TDG levels of 130 to 140 percent for a number of consecutive days, resulting in 3.2 to 

3.3 percent of the migrants exhibiting signs of gas bubble trauma. (page 49)

Comments: There were no comments on this issue. The ISAB concurs.
ISAB 2002-1 Review of Giorgi et al.

20

III. Flow Augmentation

Introduction

There are many issues in dispute regarding the relationships between river flow and 

salmon survival, and regarding the efficacy of augmenting flows to aid salmon survival. 

The existing literature, summarized by Giorgi et al., only begins to explore the 

complicated interactions of the amount of water in the river and a multitude of other cooccurring factors that may affect salmon survival. These factors are environmental (e.g., 

temperature, turbidity, overbank inundation) and operational (e.g., rapid changes in flow 

at low river volumes as a result of load following). The technical disputes arise mostly 

because of a lack of information and differing assumptions about unstudied hypotheses, 

not because of deficiencies in the Giorgi et al. summary. The technical disputes continue 

to cascade into policy disputes. 

Giorgi et al. Premises for the Flow-Augmentation Strategy

Giorgi et al. identify two premises that form the foundation of the flow augmentation 

strategy: 1) that increases in water velocity (flow) should lead to increases in migration 

speed, which in turn should lead to increases in survival of migrating juvenile salmonids. 

and 2) that lowering water temperature (summer) leads to improved migratory conditions 

for juvenile and adult salmonids, leading to increased survival. (page 60)

Comments: The ISAB finds these premises too narrow, as did the NMFS in its 

comments. The ISAB does not concur that the question of flow-survival 

relationships and flow augmentation can be reduced to these two premises. As 

noted above, there are many untested hypotheses for benefits of higher flows (and 

flow augmentation). Some of these untested hypotheses were referred to in the 

comments (e.g., NMFS’s suggestions of improved conditions in the estuary, 

larger Columbia River plume, increased turbidity to reduce predation). The ISAB 

recognizes others discussed by the ISG in Return to the River 2000 (ISG 2000). 

The potentially detrimental effects of load following at lower river flows has been 

discussed by the ISAB previously in relation to the Hanford Reach and Priest 

Rapids Dam (redd and juvenile stranding). A fuller exploration of premises is 

needed, which goes beyond the scope and time frame of the ISAB’s review of the 

Giorgi et al. report. 

Giorgi et al. conclusions regarding Speed of Outmigration of Juvenile Salmonids:

a) Impoundment of the Snake and Columbia rivers has slowed the migration speed of 

yearling chinook and steelhead smolts. (page 62)

b) Average river flow explains most of the variability in travel time of sockeye and 

steelhead smolts as well as sub-yearling chinook migrating through John Day Pool. 

In the Snake River both flow and level of smolt development are factors that interact to 

explain the migration speed of yearling chinook smolts. Travel time is more rapid for 

yearling chinook in advanced stages of smoltification in both the Snake and upper 

Columbia rivers. However, no effect of flow was found for travel times of yearling 

chinook emigrating from the upper Columbia River from Rock Island Dam to McNary 

Dam. (pages 63, 65)
ISAB 2002-1 Review of Giorgi et al.

21

c) The most dramatic responses to a given increment of flow occur at low flows, i.e. 

increases of flow of 10 kcfs have the largest effect at river flows from 40 to 50 kcfs 

(reduction in travel time of 5.0 days to 4.2 days) whereas increases of flow from 100 kcfs 

to 110 kcfs reduce average travel time by only 1/10 of a day. (page 63)

d) In the Snake River, migration speed of fall chinook has been related to flow, 

temperature, turbidity, and fish size. However, all of these factors are time related, flow 

decreases, temperature increases, and turbidity decreases, as fish size increases, making it 

difficult to demonstrate effects of a particular variable with the existing data. (page 64)

e) In the upper Columbia River, from Rock Island Dam to McNary Dam, size of fall 

chinook is the best predictor of migration speed. (page 64)

Uncertainties and Possible Sources of Dispute over Travel Times: Until NMFS and the 

Fish Passage Center provide comprehensive analyses covering the years from 1993 

through 2001 (subsequent to Berggren and Filardo 1993), the region must rely upon 

previous investigations to characterize behavioral responses of juvenile salmonids to 

volume of flow. (page 65)

Comments: The above findings and conclusions do not appear to be in dispute. 

The Joint Technical Staff Memorandum noted that Giorgi et al. had not referred to 

a recent study by Connor et al. 2001, which reports that flow can be used to 

predict travel time for juvenile fall chinook in the Snake River. The ISAB concurs 

with the findings of Giorgi et al. and also regrets that the authors did not include 

the recent work by Connor et al. However, even with use of these most recent 

results the facts available are insufficient to resolve disputes over their application 

to management decisions on flow, which relate to survival not migration speed. 

The discussion on survival follows. 

Giorgi et al. conclusions regarding Effects of Flow on Survival of Juvenile Salmonids:

Translating river flow or smolt migration rate into smolt survival is the critical issue 

underpinning the rationale for providing flow augmentation. The foundation for this 

strategy extends back to a 1981 study by Sims and Ossiander who described a positive 

relationship between average volume of river flow and average survival of yearling 

chinook and steelhead during the period of outmigration over the years 1973 to 1979. As 

noted in the general comments in the main text, Giorgi et al. chose to use mostly recent 

studies, as better representing the current conditions. (page 65)

Comments: Although others criticized this approach, the ISAB concurs. 

Giorgi et al. conclusions regarding Survival of Yearling Chinook

The NMFS White Paper on smolt survival and flow summarizes two decades of yearling 

chinook survival studies and flow indices. The authors failed to find a relationship 

between flow indices and survival for yearling chinook. Similarly, Giorgi et al. report that

Zabel et al. 2001 failed to find a flow/survival relationship. In NMFS’ White Paper 

(NMFS 2000) no relationship was found from PIT tag recovery data in the Snake River. 

Although they found a relationship of flow and migration rate, there was none between 

migration rate and survival. (page 67)
ISAB 2002-1 Review of Giorgi et al.

22

Comments. Comments from Save Our Salmon, and the Joint Technical Staff were 

critical of the White Paper and Zabel et al.’s analysis, primarily because those 

analyses depended upon a per project estimate of survival rather than a per mile 

analysis, or analysis over a longer reach (Oregon comments) which they feel is 

more appropriate, and leads to a conclusion that, taking spill into account, 

survival was flow dependent. The ISAB agrees with the comment that there is a 

distance effect that must be taken into account, and that per project results are 

likely insufficient. More analysis is needed. 

Giorgi et al. conclusions regarding Survival of Steelhead

In contrast to the results with yearling chinook, the report of Zabel et al. 2001 found a 

sharp decrease in survival of steelhead during the low flow year 2001, relative to other 

years during this decade. Giorgi et al. feel that this result was brought about by two 

factors, the strong effect of low flow that is known to increase travel time of steelhead, 

and the warm temperatures that occurred early in the steelhead migration. (page 69)

Comments. The comments focused on the data in the Zabel et al. report, which 

support the premise of a flow/survival relationship for steelhead. The ISAB has 

not conducted any independent analysis of the recent data, but generally concurs 

with the findings of Giorgi et al. and the commentors. 

Giorgi et al. conclusions regarding Survival of Snake River Fall Chinook Salmon

Three factors were found by NMFS to be significantly related to survival of outmigrating 

fall chinook salmon from the Lyons Ferry Hatchery. They were temperature, flow, and 

turbidity in that order of significance. The predictor variables were highly correlated, 

confounding the ability to identify the causative agents. Size of fish at time of release 

from the hatchery was also found to be strongly correlated with survival. Giorgi et al. 

refer to Connor et al. 1998 who, in a study of subyearling chinook from the Snake River 

above Lower Granite Dam, found that, over the period of years 1992-1995 annual 

detection rates of the fish at Lower Granite Dam were highest in the two years of average 

high flow, and lowest in two years of average low flow. (page 70)

Comments. Save Our Salmon commented that Giorgi et al. placed too much 

emphasis on the interrelationships of variables and that these should not be used 

as evidence that flow is not a strong factor affecting the observed survival rates. 

The Joint Technical Staff Memorandum and NMFS referred to Connor et al. 

2001, a paper not referenced by Giorgi et al. in which the authors report that 

summer flow augmentation increased migration speed and survival of juvenile fall 

chinook salmon in the Snake River. The ISAB concurs with the Giorgi et al. 

report that the variables are interrelated and flow, by itself, cannot be separated 

out as the causative factor for survival. Inclusion by Giorgi et al. of the work of 

Connor et al. 2001 might have helped clarify the problem. Because flow seems to

be the basis for differences in some of the other factors, the SOS comments are 

important. Although researchers have been reluctant to promote the use of simple 

statistical (regression) models to predict survival of fall Chinook as a function of 
ISAB 2002-1 Review of Giorgi et al.

23

flow, the ISAB judges that such predictions are possible and defensible. We note 

that with more or less the same precision and accuracy, it is also possible to 

predict survival as a function of water temperature or other factors that are 

correlated with flow. However, more work is needed to refine our understanding 

of these (and likely many other) factors to provide persuasive scientific 

justification for flow augmentation. 

Giorgi et al. conclusions regarding General Flow Augmentation Evaluations 

Surprisingly few, if any, comprehensive evaluations of flow augmentation have been 

published, which address all or even most of the significant issues. The annual reports of 

the Fish Passage Center are deficient in that they fail to estimate the extent to which flow 

augmentation increased water velocity or decreased water temperature as compared to 

base condition, nor do they predict the magnitude of fish response in terms of smolt 

migration speed or survival, as attributable to that incremental change in flow and 

temperature. The NMFS BO is deficient in this regard, as well. The BO specifies 

volumes (MAF) for flow augmentation, and prescribes seasonal flow (KCFS) targets, but 

provides no quantitative analysis describing changes in water velocity, smolt speed or 

survival benefits that are to be expected as a result of flow augmentation. (Pages 72-73) 

Giorgi and Schlecte conducted an evaluation for the years 1991-1995, Snake River flow 

augmentation volume ranged from an annual low of 1.35 to 2.56 MAF. These volumes 

were insufficient to sustain the flow targets established by NMFS for the duration of the 

smolt migration period. Flow augmentation did increase water velocity through Lower 

Granite Pool an average of 3-13%. During the summer, the increase was more 

pronounced, with an increase of 5-38% change in water velocity attributable to the 

addition of flow augmentation water. Corresponding decreases in travel time ranged from 

5-16% over the five years included in the study. Dreher (1998) concluded that the 

volumes of water earmarked for flow augmentation in the Snake River 1) provide only 

small incremental increases in average water velocity through the hydroelectric system, 

and 2) are insufficient to meet flow targets in all years. The study was limited in scope. 

(pages 74-75)

Comments. There were more comments on the subject of flow augmentation than 

either of the other mainstem strategies. The Idaho Water Users Association noted 

that the variation in discharge between good and poor water years in the upper 

Snake River is more than all of the storage in the upper Snake River Basin. They 

feel that between year survival/flow analysis cannot be used to evaluate flow 

augmentation effects, due to changes from year to year in other factors affecting 

survival. 

Montana Fish, Wildlife and Parks commented that flow augmentation from large 

storage reservoirs in Canada and Montana is designed to assist juvenile fish in the 

Columbia River below McNary Dam. They state that research has not validated 

the predicted benefits to anadromous fish from McNary Dam downstream. 

Research has focused on the Snake River. They state that the actual change in 

water velocity expected in the lower Columbia River as a result of augmentation 
ISAB 2002-1 Review of Giorgi et al.

24

from the upper Columbia River is minute. No benefits in terms of temperature 

amelioration in the lower river could possibly occur, given the distance from the 

source and the numerous reservoirs that intervene. This is true even though 

selective withdrawal devices are in place at Libby and Hungry Horse Dams. 

These are used to regulate the temperature of discharge immediately downstream. 

On the other hand, they point to significant adverse effects on resident fishes in 

the upstream storage reservoirs and the streams leading from them into the 

Columbia River. Montana refers to the quote in Giorgi et al. from the ISG’s 1996 

draft review (ISG 2000), indicating the potential adverse effects of flow 

augmentation on biological productivity upstream. See further comments from 

Montana below with respect to the need for a balanced approach in deciding on 

flow augmentation strategies.

Giorgi et al. conclusion regarding Effects of Augmented Flow on Water Temperature 

Leading to Effects on Survival of Juvenile and Adult Salmon and SteelheadModel Studies

Models are used to predict probable effects of releases from Dworshak and Hells Canyon 

dams on water temperature. (page 78)

A. Models predict measurable effects to extend only as far as Lower Granite Dam

1) Expected effects depend upon the volume of base flow relative to the volume of 

augmentation flow, and depend upon distance from the source. 

2) At Lower Granite Dam expected decreases usually range from 1- 4 o F, but can 

range to 6-8 o F. At Ice harbor Dam, the expected decrease in temperature is on the 

order of 1-2 o F. Cold water released upstream will tend to sink, suggesting that 

pockets of cool water might be available as refugia, but cooling throughout the water 

column will not occur.

Comments. Save Our Salmon commented that even a reduction in temperature as 

small as 1-2

o

 C can greatly affect survival rates when temperatures are near the 

lethal limit. The Joint Technical Staff referred to the Connor et al., 2001 report, 

which is not included in the report by Giorgi et al. That report concludes that flow 

and temperature together affect survival of juvenile fall chinook in the Snake 

River. The ISAB concurs with the summary of temperature results by Giorgi et al. 

but also acknowledges the point made by the SOS and the importance of the 

Connor et al. 2001 studies. The temperature issue requires additional studies, both 

empirical and modeling. 

B. Drafting water from storage reservoirs for flow augmentation adversely affects 

resident fishes in the reservoirs and immediately downstream. Expected benefits to 

anadromous fishes ought to be balanced against ecosystem function and potential risk 

to resident fishes. Giorgi et al. refer to ISG (1996; now ISG 2000), which calls attention 

to the potentially negative implications for nutrient mass balance and food web 

productivity in Flathead Lake, located downstream from Hungry Horse Dam. This issue 

involves balancing expected benefits to anadromous fish against ecosystem function 

and potential risk to other native species, including Kootenai River white sturgeon, a 

listed species. Giorgi et al. states that they did not encounter a comprehensive, 
ISAB 2002-1 Review of Giorgi et al.

25

multidisciplinary evaluation of benefits and risks to anadromous and resident fish 

species and their habitat. (pages 78-79)

Comments: Montana Fish Wildlife and Parks strongly emphasized this point. 

There were no other comments. 

The ISAB notes that we were also asked to review the situation in 1997 (ISAB 

97-3). In that (1997) report we noted that NMFS had employed a facilitator to 

attempt to arrive at an agreement among federal, state, and tribal parties on 

modification of operations called for in the BiOp (Wright, 1996). One of the 

Steering Committee Findings was “The need for and level of August flow 

requirements should be one of the region’s top salmon monitoring and evaluation 

priorities.” We agreed with that finding. The ISG in Return to the River 2000 

repeated the recommendation.

Giorgi et al. conclusions regarding Uncertainties and Potential Sources of Dispute on 

Flow Augmentation 

1. The NMFS PIT tag-based smolt survival estimates derived since 1993 form a strong 

basis for examining such a relationship between flow and survival. These efforts should 

be expanded to include the lower and upper Columbia River where and when possible. 

(page 81)

Comments. The Joint Technical Staff Memorandum believes that this is a highly 

questionable statement, since it ignores delayed effects due to migration delay, 

synchrony of smolt arrival into the estuary and overall impacts of stress and 

bioenergetics on ultimate survival to adult. Save Our Salmon commented that 

flow is liable to affect survival outside the hydrosystem. The ISAB believes the 

questions raised are legitimate ones, but do not recognize that the studies referred 

to are aimed at estimating mortality within the hydrosystem. The other matters 

raised are at another level of effects. Whether there is a way of addressing them 

satisfactorily is a more difficult question to answer. Perhaps recovery of PIT 

tagged adults will help. The high adult return rates of the most recent years do 

provide large PIT tag sample sizes with a potential for analyzing survival rates of 

different passage groups after they exit the hydrosystem -- something that was not 

feasible in years of low return rates. In any case, the ISAB concurs with the 

Giorgi et al. conclusion and urges that research be conducted toward answering 

the subsequent issues raised in comments. We recommend continued PIT tagging, 

with design considerations to include the potential for analysis of post-Bonneville 

survival of tagged groups with different passage experiences. 

2. Giorgi et al. recommendation for further studies of effects of flow. 

A) A multi-faceted, comprehensive, updated evaluation of the biological benefits and 

risks associated with flow augmentation is advisable and is long overdue. (page 82)

Comments. The Joint Technical Team agreed with this recommendation, 

suggesting that it should include lifecycle modeling to evaluate full effects of flow 
ISAB 2002-1 Review of Giorgi et al.

26

on survival. NMFS suggested several other sources of information not available to 

Giorgi et al. We concur with the recommendation for a comprehensive updated 

analysis, but repeat our warning about use of models in place of data.

B) Giorgi et al. were unable to find a comprehensive multidisciplinary evaluation of 

flow augmentation, which attempts to assess and quantify the full set of benefits and 

risks to anadromous and resident fishes and their habitat. The focus has been on 

narrow interests of the group affected. Such an analysis should be undertaken. (page 

82)

Comments. Primary support for this recommendation comes from Montana Fish 

Wildlife and Parks. There was no objection from other sources.

An issue raised in the comments from Montana Fish, Wildlife and Parks was the 

belief that release of water from reservoirs far upstream in the basin for flow 

augmentation provides little benefit to downstream migrants yet can have 

measurably detrimental effects locally. This was emphasized especially for the 

reservoirs in Montana that drain through a long chain of rivers, lakes, and 

reservoirs before the water reaches the migrant corridor in the lower river. As 

noted above, the Giorgi et al. report discussed this issue under the heading 

“Benefits and Risks to other species” in which it quoted a passage from the ISG 

(1996) draft report Return to the River (now ISG 2000), went on to identify the 

issue in the Summary on Flow Augmentation where it recommended that “The 

scope of future evaluations (of flow augmentation) need to more fully address the 

balance of benefits and risks between anadromous and resident fish resources”, 

and then identified the issue as a Critical Uncertainty and Research Opportunity. 

We note that the tradeoffs between headwater and downstream effects have been 

an important part of the flow augmentation debate for some time. See ISG 97-3 

referenced above, as well as ISG 2000. The analyses by Council’s Montana staff 

(several years ago) and the Idaho Department of Water Resources’ more recent 

reanalysis of NMFS’ smolt travel time and survival data for the Snake River 

(Dreher et al. 2000) and the ISAB review of it (ISAB 2001), along with other 

unpublished analyses cited in the comments suggest that this topic deserves more 

technical evaluation with a view toward a potential revision in management 

approaches. We would caution, however, that ability to detect a local effect at a 

storage reservoir or tailwater, even a dramatic one, should not by itself be a 

deciding criterion against flow augmentation to achieve downstream benefits. An 

intense local effect could influence far fewer fish than a more subtle effect that is 

exerted over many hundreds of miles downstream and which exposes orders of 

magnitudes more fish. Such considerations should be part of the technical 

evaluation. 
ISAB 2002-1 Review of Giorgi et al.

27

References Cited 

Berggren, T. J., and M. J. Filardo. 1993. An analysis of variables influencing the 

migration of juvenile salmonids in the Columbia River basin. North American Journal of 

Fisheries Management 13:48-63.

Bouwes, N., R., C. Petrosky, H. Schaller, P. Wilson, E. Weber, S. Scott, and R. Boyce. 

2002. Comparative survival study (CSS) of PIT tagged spring/summer chinook; Status 

report for migration years 1997-2000; Mark/recapture activities. Contract 8712702, 

Bonneville Power Administration, Portland, Oregon. 

Chapman, D. A. Giorgi, M. Hill, A. Maule, S. McCucheon, D. Park, W. Platts, K. Pratt, 

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Wenatchee WA, Douglas County P.U.D., East Wenatchee, WA, and Grant County 

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Grant County P.U.D., Ephrata, WA 411 pp.

Chapman, D., C. Peven, A. Giorgi, T. Hillman, and F. Utter. 1995. Status of spring 

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Connor, W. P., H. L. Burge, and D. H. Bennett 1998. Detection of PIT tagged 

subyearling chinook salmon at a Snake River dam: Implications for summer flow 

augmentation. No. Amer. Jour. Fish. Mgmt. 18(3):530-536

Connor, W. P., R. K. Steinhorst, and H. L. Burge. 2000. Forecasting survival and passage 

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Connor, W, P. 2001. Juvenile life history, downstream migration rate, and survival of 

wild Snake River fall chinook salmon. Ph.D. dissertation. University of Idaho, Moscow.

Dreher, K. J. 1998. A view on Idaho’s experience with flow augmentation. Idaho 

Department of Water Resources, Boise. 

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survival, flow, temperature, and migration data for hatchery-raised, subyearling fall 

chinook salmon above Lower Granite Dam, 1995-1998. Idaho Department of Water 

Resources, Boise. 
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Giorgi, A., M. Miller, and J. Stevenson. 2002. Mainstem passage strategies in the 

Columbia River system: Transportation, spill and flow augmentation. Report 2002-03, 

Northwest Power Planning Council, Portland, Oregon. 

Independent Scientific Group (ISG). 2000. Return to the River 2000. Restoration of 

Salmonid Fishes in the Columbia River Ecosystem. Report 2000-12. Northwest Power 

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Independent Scientific Advisory Board (ISAB). 1997. Ecological impacts of the flow 

provisions of the Biological Opinion for endangered Snake River salmon on resident 

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drawdown on aquatic systems in reservoirs.

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salmonids past Columbia and Snake river dams – White Paper. Northwest Fisheries 

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Snake and Columbia River dams and reservoirs. National Marine Fisheries Service, 

Seattle, Washington; draft for Bonneville Power Administration, Portland, Oregon. 

List of Comments

Committee of Nine and Idaho Water Users Association. Letter from John Simpson of 

Barker, Rosholt & Simpson and Norm Semanko of the Idaho Water Users Association to 

Mark Walker of the Northwest Power Planning Council dated March 8, 2002 (3 pages).

Joint Technical Memorandum (CRITFC, IDFW, ODFW, USFWS, WDFW, YIN). Letter 

from Earl C. Weber, Stephen Petit, Shane Scott, Steve Parker, Ron Boyce, and Howard 

Schaller to Mark Walker of the Northwest Power Planning Council dated March 19, 2002 

(12 pages).

Montana Fish Wildlife and Parks. Letter from Brian Marotz to Mark Walker of the 

Northwest Power Planning Council dated March 8, 2002 (7 pages).

National Marine Fisheries Service. Letter from Brian J. Brown to Northwest Power 

Planning Council dated May 28, 2002 (7 pages).

Oregon Department of Fish and Wildlife. Letter from Raymond R. Boyce to Mark 

Walker of the Northwest Power Planning Council dated March 20, 2002 (10 pages).

Save Our Wild Salmon. Letter from Nicole Cordan to Mark Walker of the Northwest 

Power Planning Council dated March 19, 2002 (1 page with 30-page attachment; Bouwes 

et al. 2002 listed in reference section).

U.S. Fish and Wildlife Service. Letter from Howard Schaller to Mark Walker of the 

Northwest Power Planning Council dated March 20, 2002 (2 pages).

Washington Department of Fish and Wildlife. Letter from B. Shane Scott to Mark 

Walker of the Northwest Power Planning Council dated April 1, 2002 (3 pages). 

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