ISAB RECOMMENDATIONS ON SURFACE BYPASS
Migratory Behavior of Juvenile Salmon
Bypass for Juvenile Salmonids at the Dams
Turbine Intake Screens
Spill for Fish Passage
Surface Flow Bypass Development
Tests of Prototype Surface Bypass Collectors
Premises for Surface Bypass Development
The Northwest Power Planning Council (the Council) has been directed by the Congress, in the Conference Report accompanying the Energy and Water Development Appropriations Act for the Fiscal Year 1998, to review "the major fish mitigation capital construction activities proposed for implementation at the Federal dams in the Columbia River Basin." The Council was directed to conduct this review by June 30, 1998, with the assistance of the Independent Scientific Advisory Board (ISAB).
The Council identified the Corps? development and testing of the surface bypass prototype at Lower Granite Dam and at other dams, hereafter termed "surface bypass," or "SBC," as one of five specific projects requiring attention of the ISAB. Other specific projects included installation of extended-length screens at John Day Dam and at other dams, the dissolved gas abatement program, Bonneville Dam juvenile fish passage improvements including the relocation of a bypass outfall, and adult fish passage improvements.
This report is the second part of a series developed by the ISAB to assist the Council in responding to the congressional mandate. Our previous report, ISAB 98-4, submitted in May, 1998, covered questions from the Council about the ecosystem context for mainstem fish bypass measures, about proposed installation of extended-length turbine intake screens at John Day Dam, and the proposed relocation of the juvenile fish bypass outfalls at Bonneville Dam. The ISAB requested an extension of time, to September 1998, to develop this response to questions regarding development of surface bypass for juvenile salmonids and abatement of supersaturated gas caused by hydroelectric project operations. Questions on the Corps' gas abatement project are addressed in a companion report (Part II. B. ISAB 98-8). We were aided in our review by a briefing by the Corps and concerned agencies on July 15, 1998 and numerous reports and reprints of published literature.
Due to the amount of time available for preparing this report, the ISAB focused on the immediate question of whether the surface flow bypass technology shows sufficient promise to warrant continuing development under the existing configuration and operation of the hydroelectric system. The more detailed suite of questions posed by the Council in its charge to the ISAB in January of this year will be addressed in the final report of the ISAB on the Corps? capital construction program in January 1999.
The immediate question before the ISAB is, "Do the preliminary tests in prototype indicate that the surface flow bypass technology shows sufficient promise to warrant continuing development?" Under the presumption that the system of hydroelectric dams retains its present configuration and operations, the answer is "Yes". It is important to note that this is not a blanket endorsement of surface bypass technology, since the efficacy of surface bypass technology will need to be established for each individual dam. The epitome of successful surface bypass is known as the Wells Dam concept. However, as a consequence of structural differences between Wells Dam and the other dams, the Wells Dam concept will need to be adapted to the configuration of each dam through development and testing of a prototype.
ISAB RECOMMENDATIONS ON SURFACE BYPASS
The following summary recommendations on surface bypass will be more fully developed in the final report on the Corps? capital construction projects to be delivered in January 1999.
- The Corps should continue development and testing of surface bypass prototypes in consideration of the following recommendations.
- Careful consideration needs to be given to the locations within the hydroelectric system where surface bypass would do the most good.
- Priority needs to be given to understanding the effect of surface bypass on federally listed species, however the effects of surface bypass on all species and life history types of native fishes needs to be understood.
- Development needs to take into account the need to protect the widest possible biological diversity.
- An aggressive, nontraditional approach to prototype development, which involves fast-track design, construction and testing, should be pursued.
- A time period of approximately ten years should be provided for the developmental phase of surface flow bypass systems to ensure proper and full evaluation.
- Testing should focus on developing data to evaluate the basic set of premises or hypotheses on which surface flow bypass is based.
- A set of alternate hypotheses should be articulated for future testing in the event that any of the basic hypotheses are rejected.
- Development of surface bypass and development of gas abatement measures are closely related and they therefore need to be consistent with each other.
In Return to the River (ISG 96-6) the Council's Independent Scientific Group undertook a detailed, thorough review of bypass measures being undertaken for juvenile salmon and steelhead at mainstem Columbia River and Snake River dams. The chapter dealing with that subject was subsequently revised and issued separately by the Council (Whitney et al. 1997).
Evaluation of the Corps of Engineers projects to develop surface bypass facilities (collectors) for juvenile salmonids requires an understanding of the basic problem whose solution is being sought, as well as an appreciation of work that has led up to the decision to attempt the development. Development of surface bypass was first mentioned as a recovery tool for threatened and endangered salmon in 1993 by the Snake River Salmon Recovery Team in their first report to NMFS (SRSRT 1993; NOAA, 1995). In a subsequent report to the Northwest Power Planning Council, Harza presented specific surface bypass design concepts, including cost estimates, with a recommendation to proceed with testing at Lower Granite Dam (Harza 1994). The Independent Scientific Group made a recommendation for surface bypass in 1996, concluding, "Surface collectors are the most promising devices for attaining the fish passage goals established by the council in the FWP or NMFS/NOAA in the Snake River Salmon Recovery Plan." (ISG 96-6, p. 308). In addition the Council's Fish and Wildlife Program calls upon the Corps and the mid-Columbia P.U.D.s to explore new approaches for fish bypass technology, including surface bypass systems, and surface spill. See Whitney et al. (1997) for further details.
Migratory Behavior of Juvenile Salmon
In addition to the reports cited above (Whitney et al. 1997 and ISG 96-6) the review by Johnson and Dauble (1995) is particularly valuable as a basis for the following discussion on migration. As they move downstream in the mainstem Snake and Columbia rivers, juvenile salmon are located primarily in the upper portion of the water column, mostly within about 30 to 35 feet of the surface. When they encounter a dam, they can pass by several routes. The primary routes for passage are the turbine intakes or the spillway. Because the turbine intakes extend from near the river bottom upward usually to within about 35 feet of the surface, the route through the turbines requires that the bulk of the fish move downward to enter the turbine intakes. Evidence has accumulated showing that passage through turbines occurs mostly at night. On the other hand, when surface passage routes exist, the fish use them rather uniformly throughout the 24-hour period.
Differences exist in migratory behavior among the salmon species and among stocks with different life history patterns. There have been apparent shifts in the annual timings of the juvenile emigration, as a whole, due to changes in relative abundance of the life history types, which can have different migratory timings. At the present time, the bulk of the emigration occurs in the spring months (April, May and June). While some subyearling chinook are present at that time, they also show an increase in abundance later in the summer (July and August).
A final but crucial aspect of migratory behavior in juvenile salmon is the tendency to follow the bulk flow as it approaches the powerhouse. Juvenile salmon tend to be in the upper 30 to 35 feetof the water mass and the direction and velocity of its movement direct the movements of the juveniles. The tendency to follow bulk is a factor in the successful surface bypass at Wells Dam (Mike Erho and Gary Johnson, personal communication). See the section below on Wells Dam for further information.
Bypass for Juvenile Salmonids at the Dams
Turbine Intake Screens
When the hydroelectric system on the mainstem Columbia and Snake rivers was under development, provision was made for upstream passage of adult salmon and steelhead, but there was not a universal understanding that there was a need to provide passage facilities for juveniles. It was not until development was well underway that studies demonstrated that juveniles passing through the turbines experienced substantial levels of mortality, in the range of 11% to 15% in the first studies. The Corps and other developers were faced with the challenge of developing a technology that would reduce this level of loss, and of retrofitting dams that were already built. Investigators at the National Marine Fisheries Service developed a concept of a traveling screen at the entrance to the turbine intakes that would divert the fish upward into gatewells where they could be collected and routed around the dam. Prototype designs were tested beginning in 1969. When Lower Granite Dam was built in 1975, it included a full array of intake screens. The technology has been improved over the years, and continues to improve as tests of various prototype designs have been conducted. The measure of success is the percentage of fish approaching the turbine intake that are successfully diverted by the screens. This measure is the fish guidance efficiency (FGE) of the screens. All four of the Snake River dams are now equipped with turbine intake screens, as are all but The Dalles Dam in the lower Columbia River. Three of the eight Snake-Lower Columbia River dams have extended length turbine intake screens (Lower Granite, Little Goose and McNary). In the mid-Columbia Reach, only Wells Dam has a fully functioning bypass system for juvenile salmon. It is a surface collection system, not an intake screen system. We will describe it in the text below.
Effectiveness of turbine intake screens seems to have approached an upper limit where large increases in the fraction of juveniles diverted are not likely to occur. No known type of bypass system is completely effective at keeping juvenile salmon away from the turbines at operating hydroelectric dams. Even when taken to the limits of available technology, intake screens are unlikely to prove 100% effective in diverting juvenile salmon (Office of Technology Assessment, 1995, p. 127). Indeed, intake screens have not so far been able to achieve the goal of 80% diversion for all federally listed species (Whitney et al. 1997).
Spill for Fish Passage
The deliberate use of spill as a passage route for juvenile fish has evolved since 1980, when a FERC agreement called for a specified percentage of river flow to be spilled during the spring emigration at the P.U.D. projects in the mid-Columbia Reach. When the Council adopted its first Fish and Wildlife Program it included provisions for spill during the spring. Currently, the 1994 Fish and Wildlife Program of the Council calls for 80% fish passage by safe routes, which includes fish diverted from the turbine intakes into a bypass system, as well as fish in spill. The Biological Opinion of NMFS/NOAA contains the same standard. Because the turbine intake screens alone will not accomplish the 80% standard for all species, spill must be added in sufficient amounts to supplement what the screens can achieve.
Implementation of this 80% fish passage efficiency (FPE) standard is complicated by the difference in effectiveness of the screens for particular species and life history types of the fish, and by differences among individual dams. Generally, the screens are most effective for yearling chinook, coho and steelhead, less so for sockeye, and least effective for subyearling chinook. To achieve the 80% fish passage standard, spill must be added to supplement the FGE of the screens. To determine a level of spill achieving the 80% fish passage standard involves settling upon a composite FGE percentage derived from the different percentages of the particular fish expected to be diverted by the screens. A separate composite percentage is set for each dam in the Snake and Lower Columbia River. In the spring, since the large majority of the fish show high values of FGE for the screens, the composite FGE number is heavily weighted in their favor, to the disadvantage of sockeye and subyearling chinook. This problem becomes somewhat academic in the final analysis because the spill amounts required could not be achieved because of water quality standards that limit gas supersaturation produced by spilling the requisite amounts of water. In 1998 in response to this dilemma, NMFS shifted emphasis from requiring that the 80% fish passage standard be met, to setting spill levels at each project that are expected to meet the maximum 120% gas saturation standard (Gary Fredericks, NMFS Portland, personal communication). Note that in the case of the mid-Columbia P.U.D. dams, spill amounts are set through a FERC process.
Surface Flow Bypass Development
The natural behavior of juvenile salmon, previously described, places them predominantly in the upper portion of the water column. As alternatives to turbine intake screens are considered, developers hope to make use of this characteristic behavior. It has been observed that where spill can be drawn from the surface, it is more effective in attracting fish than spill drawn from deeper water. Modification of spill gates is being investigated as a possible means of improving fish passage efficiency while maintaining spill volumes at levels that will meet water quality standards. Preliminary tests with sluiceway gates that were already designed to draw from surface waters have shown promise.
The primary source of encouragement for surface flow bypass development is the success at Wells Dam in the mid-Columbia Reach. Wells Dam includes the first successful surface flow bypass system for juvenile salmon. Testing of a prototype began in 1983. Full installation across the powerhouse was complete in 1989. Studies over the next three years showed that the bypass was successful in passing 89% of the juvenile fish that passed the dam, both in spring and summer (Skalski, 1993). To date, it is the only system in the Columbia Basin that achieves the 80% fish passage standard without the addition of spill.
One of the reasons for the success of surface collection at Wells Dam is the particular design of the dam itself, known as a hydrocombine, in which the spillway is located directly above the turbine intakes. Hydraulic model studies indicated the feasibility of the concept. In the prototype and final design, solid baffles were placed in front of the spillway entrances to a point 30 to 40 feet below the surface. In five of the eleven enclosed spillbays a vertical slot was left open for passage of water and fish in the center slot of those spill bays. Opening the top leaf of a spillway gate provided fish attraction flow that kept the fish in the upper strata of the water column, rather than sounding to pass through the turbine intakes (Johnson, 1995).
Another reason for the success of surface bypass at Wells Dam is that juvenile salmon generally follow the bulk flow into the forebay. Juvenile salmon are usually found in the upper 30-35 ft of the flow approaching the 1000-ft width of the hydrocombine. The turbine units draw from deep in the water column, and the lines of flow into the turbines are relatively flat. Hence the combination of fish distribution and hydrocombine hydraulics make it likely that the juvenile salmon will encounter one of the surface bypass entrances at Wells Dam.
The design and configuration of the entrances also play important roles in the success of Wells Dam surface bypass. Placement of the five entrances across the powerhouse is designed to ensure encounters by juvenile salmon. In addition to location, three factors are key to the success of the entrances; large size, appropriate acceleration coefficient (Arnold 1974), and high volume of flow relative to total discharge (Gary Johnson and Mike Erho, personal communications).
Tests of Prototype Surface Bypass Collectors
The surface bypass technology developed at Wells Dam is not directly transferable to other dams on the Snake River or mainstem Columbia River. The design of Wells Dam, the hydrocombine, is fundamentally different from the design of all other Snake and Columbia mainstem dams. Hydrocombines have the spillway located directly above the powerhouse, whereas the other mainstem dams have spillways located separately from the powerhouse.
It would be premature to review the details of specific results of SBC testing. We have been fully briefed on the status of the SBC research program being conducted by the Corps at Lower Granite Dam, and Bonneville Dam powerhouses. We have also been briefed on feasibility analyses at The Dalles and John Day dams. In addition, we have been briefed on the results of 1996 and 1997 prototype tests by Chelan County Public Utility District (P.U.D.) at Rocky Reach Dam and by Grant County P.U.D. at Wanapum Dam. Preparatory to this report, the Corps and Chelan P.U.D also briefed the ISAB on the preliminary results of their studies in the spring of 1998.
In all cases, significant progress has been made in identifying the relative effects of features of the prototypes. At Lower Granite Dam, there was an increase in 1998 in the percentage of fish that were diverted into the surface flow bypass. Tests by the Corps at Bonneville, The Dalles and John Day dams were of a preliminary nature, but the results are promising enough to justify larger scale testing. The Dalles Dam in particular, offers the potential for development of a surface flow bypass because the ice and trash sluiceway, located above the turbine intakes, already operates in that mode. It passes 40% or more of the fish approaching the powerhouse in its present configuration. There is a strong possibility that its effectiveness can be improved by design modifications.
At Rocky Reach Dam in 1998, it was found that an additional upstream opening intended to attract more fish was not effective. Ideas for a revised design have resulted. These will be incorporated into prototype tests scheduled for 1999.
At Wanapum Dam it was found that the prototype surface flow bypass was not sufficiently effective in collecting fish, but that it was effective in diverting a high percentage of the fish away from the turbine intakes and toward the spillway. While no modifications to the prototype were made for testing in 1998, it was left in place to function in that way, pending a decision as to its future.
In the same context, surface spill is being investigated as a bypass alternative. Tests of spill gate configurations that will draw surface water are being conducted at Rock Island and Wanapum dams and are being planned for John Day Dam.
Premises for Surface Bypass Development
In order to understand and manage the effects of scientific uncertainty on implementation of salmon recovery technologies, it is important to proceed under a guiding set of hypotheses -known as a conceptual foundation. Given the present configuration and operation of the hydroelectric system, development of surface bypass is consistent with the conceptual foundation of the Independent Scientific Group to the extent that it takes advantage of the natural behavior of the emigrating juvenile salmon (Coutant 1997). It is important for more specific hypotheses to be presented and tested regarding how surface bypass technology can improve the expression of diversity among salmon populations.
More specific hypotheses to guide development of the surface bypass prototypes have been developed for the U.S. Army Corps of Engineers. The premises for surface flow bypass (SFB), development, as articulated by Gary Johnson (Battelle Laboratory) reflect the researchers? present understanding of fundamental smolt behaviors. The premises are:
- Bulk Flow -- Smolts follow the bulk flow as they migrate toward the dam. This dictates their lateral and vertical position in the forebay and predisposes them to pass at certain sites horizontally along the face of the dam. (Far zone > 150 ft [50 m])
- Opportunity for Discovery -- Smolts are primarily distributed in the upper portion of the water column, prefer not to sound to pass dams, and are horizontally distributed such that they are predisposed to readily pass the dam via a SFB. Smolts can sense the vertical and horizontal components of the flow regime and use this information to select migration paths. These behaviors allow smolts the opportunity to discover the SFB as they move into the near zone. (Intermediate zone 30-150 ft [10-50 m])
- Entrance Conditions ? Smolts will actively migrate into and stay within a SFB entrance provided surface flows smoothly accelerate or decelerate, and acoustical, optical, and biological conditions are conducive to passage. Entrance conditions include near zone flownets, total volume, velocity gradients, shape, horizontal/vertical orientation, light, and surface area. (Near zone: 0-30 ft [0-10 m])
- Conveyance ? Smolts will migrate safely in conveyance structures, such as channeled flow, dewatering systems, and spillbay-type bypasses.
- Outfall ? Smolts are not injured in the outfall environment, and will migrate in the bypass flow as it egresses the tailrace.
The premises need to be constantly refined and tested against the best available literature records, as well as against the data developed in the course of testing.
We stress that the ISAB does not regard these premises as merely working assumptions. These are all testable hypotheses for which data are to be collected and evaluations conducted. In future reviews, when these hypotheses are presented, evidence justifying their retention should also be presented. If data for retention are not available, alternative hypotheses should be presented.
We also stress that these premises are not the only applicable concepts. For example, under the Corps? premise 3, a smooth flow field is needed in the forebay to attract fish to the collector. We believe an equally viable alternate premise 3 is that the fish need turbulent attraction flow, and not a smooth flow field. Development and evaluation of alternatives is critically important at this point in the process of SBC development.
In addition to the flow field hypotheses, there are many other alternative hypotheses and premises that need to be developed. For example, the five premises of this section presume that there is one biological entity, the smolt, for which the SFB is applicable. The five premises could be expanded to include known and inferred behaviors of multiple life history types within the salmon species, as well as of other species, such as Pacific lamprey.
Consequently, it is important for the Corps to develop a set of alternative hypotheses for evaluation. The surface bypass technologies are so new that having good alternative premises is essential to prevent spending more money and time than necessary on designing and implementing features that the fish must have for effective orientation to the surface bypass apparatus.
- Over 20 years of work to improve turbine intake screen technology has not yet developed a turbine intake screen that can achieve the 80% fish passage efficiency (FPE) standard for all species and stocks. It is time to find an adjunct to the screen technology for bypass.
- Surface collection continues to show promise as a bypass measure for juvenile salmonids.
- Spill must be provided in an amount to make up the difference between the 80% FPE standard and the FPE actually achieved by turbine intake bypass screens.
- The surface collector at Wells Dam is the only bypass system in the basin that achieves the 80% FPE goal without the addition of spill.
- Surface bypass technology may be able to reduce the amount of spill needed to achieve the 80% FPE standard.
- The surface bypass technology is not directly transferable from Wells Dam to other projects because of their different spill way configurations.
- Current SBC evaluations speak primarily to the issue of the potential efficacy of the surface bypass apparatus and not as much to the specific percentages or numbers of fish that may have been influenced by its presence.
- Substantial uncertainties remain regarding the level of changes in survival of juvenile salmon that will be provided by SBC, and regarding how these changes in survival will be distributed across listed species, and across the other life history types of the non-listed species.
- Development and application of surface bypass technologies is necessarily a slow process because of logistical constraints on the testing of prototypes. The investigators have only a limited number of alternative configurations that they can test during a given emigration season.
Arnold, G. P. 1974. Rheotropism in fishes. Biological Review 49: 515-576.
Coutant, C. C., L. D. Calvin, M. W. Erho, Jr., J. A. Lichatowich, W. J. Liss, W. E. McConnaha, P. R. Mundy, J. A. Stanford, R. R. Whitney, R. N. Williams, D. L. Bottom, C. A. Frissell. 1997. The normative river: an ecological vision for the recovery of Columbia River salmon.
Pages 50-59 in D. J. Mahoney, editor. Waterpower ?97. Proceedings of the 1997 International Conference on Hydropower. American Society of Civil Engineers, New York.
Harza 1994. Review of Reservoir Drawdown - Final Report. 1994. NW Power Planning Council (Portland, OR), Columbia/Snake River Drawdown Committee. Harza and Associates, Portland OR.
ISAB 98-2. 1998. Response to the Questions of the Implementation Team Regarding Juvenile Salmon Transportation in the 1998 Season (February 27, 1998). Independent Scientific Advisory Board for the Northwest Power Planning Council, Portland, OR, National Marine Fisheries Service, Seattle, WA.
ISAB 98-4: First Report: The ISAB Corps Capital Construction Project Review. The Scientific Basis for Juvenile Fish Passage Improvements in the Federal Columbia River Power System: John Day Extended Length Turbine Intake Screens and Bonneville Dam Bypass System Outfalls (June 9, 1998). Independent Scientific Advisory Board for the Northwest Power Planning Council, Portland, OR, National Marine Fisheries Service, Seattle, WA.
ISAB 98-8. Report of the Independent Scientific Advisory Board Review of the U.S. Army Corps of Engineers? Capital Construction Program, II. B. Dissolved Gas Abatement Program. Independent Scientific Advisory Board for the Northwest Power Planning Council and the National Marine Fisheries Service.
ISG 96-6. 1996. Return to the River. Report to the Northwest Power Planning Council, Independent Scientific Group. 584 pp.
Johnson, G.E. 1995. Fisheries research in the forebay of Wells Dam in spring 1995 related to the surface flow smolt bypass. Pacific Northwest Laboratory. Report to U.S. Army Corps of Engineers. Contract No. 19478 Task 12.
Johnson, G.E. and D.D. Dauble 1995. Synthesis of existing physical and biological information relative to development of a prototype surface flow bypass system at Lower Granite Dam. Final Report to U.S. Army Corps of Engineers, Walla Walla, WA.
NOAA 1995. Biological Opinion on 1994-1998 Operation of the Federal Columbia River Power System and Juvenile Transportation Program. Reasonable and Prudent Measure 11. March 2, 1995.
Office of Technology Assessment 1995. Fish Passage Technologies: Protection at Hydropower Facilities. OTA-ENV-641. Washington, D.C.. U.S. Govt. Printing Office. September, 1995. 167 pp.
Skalski, J. R. 1993. Summary of 3-year bypass efficiency study at Wells Dam. Processed Report. Public Utility District No. 1 of Douglas County, East Wenatchee, Washington. 5pp.
SRSRT (Snake River Salmon Recovery Team; Bevan, D.E., P.K. Bergman, T.C. Bjornn, J.A. Crutchfield, J.P. Harville, P.C. Klingeman, and J.W. Litchfield) 1993. Draft Snake River salmon recovery plan recommendations. NMFS/NOAA, Portland, OR. 364 pp.
Whitney, R.R., L.D. Calvin, M.W. Erho, Jr., and C.C. Coutant. 1997. Downstream passage for salmon at hydroelectric projects in the Columbia River Basin: Development, installation, and evaluation. Northwest Power Planning Council. Report 97-15. 101 pp.
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