|Seven electrodes at a Swiss hydroelectric plant upstream of the tailrace confluence with River Arve are visible in the array's non-conductive concrete on the left bank of the tailrace.|
Improving technology designed for deterrence offers hydroelectric facility managers options to both control and protect fish as they move through and around hydro projects.
By Carl V. Burger, John W. Parkin, Martin O'Farrell and Aaron Murphy
Carl Burger, a former fisheries administrator for U.S. Fish & Wildlife Service, is senior scientist at Smith-Root Inc. John Parkin, P.E., is president of Parkin Engineering Inc. Martin O'Farrell, PhD, is director of European business at Smith-Root Inc. Aaron Murphy, P.E., is a project manager at 3J-Consulting.
The hydropower community faces constant challenges to prevent fish from entering tailraces and intake canals. Different deterrence technologies have been applied, with varying degrees of success. Mild fields of pulsed, direct current (DC) electricity have been used extensively in North America and Europe, and hydropower facility managers have also used electric deterrence arrays to guide fish toward desirable passage locations or away from areas where fish presence is unwanted.
One of several successful electrical applications employs the Graduated-Field Fish Barrier (GFFB). Designed and manufactured by Smith-Root, Inc., Vancouver, WA, this non-lethal technology intensifies voltage gradients as fish attempt to move upstream in tailraces. When fish are oriented upstream (perpendicular to electrodes), they are "head-to-tail" parallel with the flow of electric current and receive the strongest effect (see Figure 1 on page 52). Behavioral deterrence results when fish turn sideways to experience a much weaker field, become less hydrodynamic and are swept downstream by water velocity.
GFFB technology has current and potential applications for fish conservation in hydropower tailrace and draft tube applications.
Electric deterrence technology once used alternating current (AC) in attempts to keep fish out of irrigation ditches in the Columbia River Basin.1 In the mid-1900s, electric fields were being used to prevent invasive sea lamprey from reaching spawning habitat in tributaries of the Great Lakes.3 These early efforts were largely unsuccessful because constant, sinusoidal AC waveforms increase the potential for fish injury. Pulsed DC offers many safety improvements (e.g. a unipolar waveform that introduces electric pulses for only fractions of each second of use) and is thus far less injurious to fish.2 Pulsed DC also allows manipulation of pulse width, giving operators additional control over power output.
GFFB technology employs a series of parallel electrodes (graduated in power intensity) that are placed perpendicular to stream flow in either tailrace or draft tube applications. Using a series of DC pulse generators, each successive electrode pair can be independently and remotely controlled to deliver progressively stronger voltage gradients, thus producing increasingly intense electric fields. The increasing electric current is an irritant/deterrent, which causes fish to turn away. If fish continue moving into increasing current, they experience temporary immobilization and will fall back with the flow until they recover (see Figure 1). Thus, water velocity is leveraged with electric field intensity to produce deterrence (the stronger the velocity in a draft tube or tailrace, the easier to turn fish away). Depending on the species, life stage and conductivity, GFFB power outputs are easily adjusted and can achieve up to 100% deterrence.
|Figure 1 Fish Deterrence This figure illustrates the operating concept for a GFFB electrode array mounted on a stream bottom (left) and its deterrent effect on fish (right). Fish encounter progressively stronger electric gradients as they move into the graduated field.|
In an initial study of the physical effects of GFFB technology on fish, adult coho salmon were exposed to GFFB fields from 0.2 to 0.9 volts per centimeter for 10-second intervals (longer than those experienced in usual guidance applications) by moving caged salmon over a live electrode array.4 A total of 16 gravid females and 16 sexually mature males were used in this study to evaluate effects on development and hatching of eggs (the gametes originated from GFFB-exposed parents). No injuries to adults and no effects on egg viability or embryo development were found. Mean mortality of eggs taken from exposed adults was 7.2% versus 8.5% in non-exposed control lots; developmental abnormalities in exposed lots was 0.3% versus 2.7% in controls.4
Electric guidance technology is becoming more widely used in the hydropower community as facility operators become more informed about its fish conservation capabilities. However, the technology has a more extensive and comparatively longer history in resource management applications to block movements of invasive species.
Description of technology (safety and operating principles)
Figure 2 on page 55 shows typical specifications of a GFFB electrode array and how the migrations and movements of fish can be re-directed towards a fish ladder, side channel or bypass canal. Fish length and body surface area affect fish deterrence and guidance. Large and long fish receive more of the electric current than smaller fish. Thus, the graduated nature of the array's output power (typically 0.2 to 1.2 V/cm; see Figure 2) means that adults will be blocked near the entry where fields are weakest, while small or juvenile fish are deterred near the middle of the field, where the gradient is stronger. This design offers an ability to block mixed species and size ranges (or to guide them into alternative channels or fish ladders when needed; see Figure 2). It is also helpful when the goal is to prevent all fish from entering tailraces and draft tubes when hydropower operators are required to eliminate or reduce injury risks for various species and size ranges attracted to outflows.
Pulse frequency is often the primary cause of fish injury.2 Guidelines for the use of electrofishing by federal and state biologists to sample endangered fishes suggest initial pulse frequency settings of 30 Hz (30 pulses per second) and voltages of 100 V, depending on water conductivity.5 Pulse frequencies below 30 Hz are considered the least injurious.2 GFFBs typically use pulse frequencies of only 3 to 10 Hz (depending on locations and needs), values much lower than those suggested for electrofishing protocols and those (60 Hz) used in AC technologies. Note that if a fish were to reach the upstream end of a GFFB array (typically not possible), they would experience a maximum voltage gradient of 1.2 V/cm of body length in most applications. Thus, for a fish of 50 cm in length (~20 inches), the maximum voltage would be 60 V.
Electric guidance arrays are not typically dangerous if used with safety precautions and protections. Proper signage, community outreach and appropriate shielding are safety necessities when using electric guidance technology. Telemetry, water-level sensors and physical motion detectors can help minimize safety risks. While sources urge caution at electric barriers,6,7 some acknowledge the much higher degree of safety associated with modern electric barriers,7 particularly the GFFB.
We found no documented case of human injury or mortality resulting from the use of an electric barrier or GFFB. Two animals were found dead at electric guidance barriers near fish hatcheries (apparently stunned by electrodes during low-water, cold-weather conditions when flows were insufficient to carry the animals downstream). Similar outcomes have been precluded since 2006 by installation of motion detectors synchronized with loud horns at these facilities. A report was received from USFWS that two people capsized a canoe and floated through an operating electric sea-lamprey barrier in Michigan in the mid-1990s. However, no injury resulted.
GFFBs for guidance of upstream-moving fish
GFFB technology has demonstrated success in its ability to block upstream movement of invasive fish.8 Also, four GFFB barriers currently guide Pacific salmon to holding ponds at federal fish hatcheries in the Pacific Northwest of the U.S. A report is available that addresses the efficiency of a GFFB to prevent fish from entering a hydropower tailrace.9 As highlighted in papers we reviewed, weak fields of pulsed DC (0.15 – 1.0 V/cm) can be effective when using GFFBs to alter fish behavior or re- direct or block movements.10
Fish management applications
GFFBs have prevented range extensions of invasive fish species. An overabundance of common carp led to a GFFB installation in the Heron Lake watershed in Minnesota, to prevent inter-lake movements. A two-year evaluation demonstrated that none of 1,600 fish tagged downstream of the barrier were among 3,367 fish captured upstream. An evaluation of the effectiveness of a GFFB in a Michigan tributary of the Great Lakes to control invasive sea lamprey found that of 1,194 lampreys tagged downstream, none were found in upstream locations.11
The performance of an electric deterrence barrier in the Chicago Sanitary and Ship Canal for invasive carp control has been evaluated.12 Radio tags were implanted in 130 common carp surrogates released downstream of the barrier. Over the four-year study, the authors located a single tag immediately upstream of this barrier; the tag never moved subsequent to its discovery.
In the San Joaquin River in 1992,13 an electric barrier was used to guide chinook salmon into the Merced River (having abundant spawning habitat) and to minimize straying elsewhere. When the electric barrier was in operation, only 11 of 988 fish did not reach the Merced River.13
Vessy hydropower application
The effectiveness of a hydropower tailrace GFFB for a power generation facility at Vessy, Switzerland, was evaluated.9 Key points in the consultant's report include:
-- Fish did not enter the tailrace and were effectively guided along the bed of the River Arve. In fact, whether these fish were fall trout or spring barbel, a comparison of fish present in the tailrace to catches in the traps of both fishways showed that migrating spawners did not have a propensity to wander into the tailrace.
-- None of 339 brand-marked trout put into water of the River Arve in mid-October 2008 … just downstream of the barrier and plant … were found in the tailrace one month later. Extensive electrofishing surveys in the tailrace upstream of the GFFB confirmed the efficiency of the electric barrier in moving marked trout upstream in the River Arve instead of into the tailrace. Further, those surveys indicated the GFFB's prevention of fish becoming trapped above the barrier at the foot of the hydroelectric plant.
-- The effectiveness of the electric barrier system explains the insignificant presence of fish observed in the tailrace.
GFFBs for guidance of downstream-moving fish
Protection and diversion of downstream-moving fish at hydropower facilities is a challenge because barrier reaction times are shortened as fish move with flowing water. Several authors have evaluated GFFBs for downstream fish guidance.14,15 We review two studies.
Duke Power study
This study evaluated fish responses in both upstream and downstream deterrence scenarios using GFFB technology under simulated hydropower conditions (and in gradually increasing electric gradients from 0.5 to 3.0 V/cm).16 The research goal was to assess whether fish entrainment could be minimized at Duke Power hydro facilities with electric barrier technology applied during different hydropower operations. Upstream tests demonstrated fish deterrence levels of 97% during simulated power generation and non-generation trials; downstream deterrence trials demonstrated lower guidance efficiency (83%).
|Figure 2. GFFB Conceptual Drawing This figure shows a conceptual drawing of GFFB specifications and graduated-field technology used to guide fish away from unintended areas towards desirable bypasses, fish ladders and side channels.|
"Inasmuch as the GFFB was successful in blocking the movements of species of fish during the modes of operation that were associated with hydropower operations in this demonstration study, it would appear that an electrical barrier may help to minimize fish entrainment losses at hydropower projects; however, this requires additional study," according to the authors.
Sacramento River (Wilkins Slough) downstream diversion study
A pump station at Wilkins Slough in Bureau of Reclamation District 108 draws Sacramento River water for irrigation purposes in California. The district's goal was to reduce entrainment of Endangered Species Act-listed chinook salmon while still allowing water diversion to occur. Two deterrence technologies were assessed. Results showed inadequate performance by an acoustic technology.15 However, the authors found a 79% entrainment reduction of marked chinook salmon juveniles with the GFFB.
Although that reduction was significant, it was deemed insufficient by federal agencies that required a 95% reduction to meet ESA criteria. Barrier installation engineers later suggested that the electric array might have been undersized and positioned too close to the diversion canal's Sacramento River entrance. A number of lessons were learned. Use properly sized electrode arrays, position them further upstream to affect behavior well before fish encounter a pump station or diversion canal, and thus reduce downstream "approach velocities" experienced by fish at diversion canal entrances.
Prospective uses of GFFB technology for hydropower
The ability to prevent fish entry into hydropower draft tubes is a global necessity for fish conservation needs among hydropower operators. Fish entry into draft tubes can occur quickly, prior to preventative stoplog deployments.
To prevent fish entry at a power plant in the United Kingdom, rectangular GFFB electrode arrays were fitted into the draft tubes of a twin, 1.6-MW Kaplan generating station (Beeston) on the River Trent, Nottinghamshire, in 1999. Residual flows from draft tubes attracted a few large fish that were subsequently injured at startup.
In a report providing information on this electric barrier and a further lesson learned, the authors state, "When initially commissioned, power was switched off when the plant shut down. After two bream were found severed below the plant (probably due to a collision with runner blades), the operation was altered to keep the electric barrier continuously energised. Since then, no further problems have occurred."7
Examination of this plant after the barrier's operational adjustment revealed, "No damaged fish were observed during a 2003 survey at Beeston."17 Thus, technical reports on Beeston plant operation indicate barrier effectiveness. The issue was resolved by keeping the electric barrier technology powered even when the plant was not fully operational.
Researchers evaluated the effect of a novel GFFB design on the behavior of adult white sturgeon.18 This innovation uses a soft-start algorithm programmed into the array's DC pulse generators, a design that induces a gradual ramp-up of power to slowly move fish away from bottom-mounted electrodes before full operation is achieved. The authors reported success in motivating sturgeon to avoid and/or leave areas near the electrode arrays at start-up.
Additional GFFB innovations for prospective hydropower applications include the ability to use sweeping electrical fields to sequentially move fish from specific areas,18 and vertically suspended electrode arrays in deep columns of water.
Our review of GFFB technology and its potential for the hydropower community suggests the ability to successfully guide, direct and deter the movements of fish to meet fish passage goals and the priorities of hydropower managers. It can do so with a history of no known injuries to humans. Deterrence systems can also be installed in waterways having considerable volume. For example, the Chicago Sanitary and Ship Canal is over 50 m wide and 7 m deep. Since 2002, the U.S. Army Corps of Engineers has relied on the complex GFFB deployment in this system to prevent invasive carp colonization of the U.S. Great Lakes.19
Keeping fish out of draft tubes during electricity generation and dewatering presents a challenge to hydropower operators. More than 1,000 steelhead trout were trapped and killed in a draft tube at Dworshak Dam and Reservoir in Idaho during routine dewatering for maintenance in 2010.18 The Beeston project provides an example of what can be done to preclude fish entry into hydropower draft tubes. These types of electric deterrence arrays can be programmed to turn on (ramp-up) in synchrony with dewatering maintenance or reduced power demands, potentially saving fish from lethal encounters with turbine runner blades and hours of staff time in removing trapped individuals.
The accounts we have reviewed demonstrate that GFFB guidance arrays can offer an important tool for the hydropower management community in efforts to protect and conserve valuable fishery resources. Perhaps most important and relevant is that electrode system installations at hydropower draft tube exits can power up when turbines power down, thus preventing fish (otherwise attracted to these sites) from entering draft tubes.
1Baker, S., "Fish Screens in Irrigating Ditches," Transactions of the American Fisheries Society, Volume 58, 1928, pages 80-82.
2Reynolds, J.B., Electrofishing, American Fisheries Society, Bethesda, Md., 1983.
3Applegate, V.C., B.R. Smith, and W.L. Nielsen, "Use of Electricity in the Control of Sea Lampreys: Electromechanical Weirs and Traps and Electrical Barriers," Fisheries Bulletin, Vol. 92, Washington, D.C.,1952.
4Hilgert, P.J. "Evaluation of a Graduated Electric Field as a Fish Exclusion Device," Report to Puget Sound Power and Light Company, Beak Consultants, Kirkland, Wash., 1992.
5"Guidelines for Electrofishing Waters Containing Salmonids Listed Under the Endangered Species Act: June 2000," National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Portland, Ore., 2000.
6"Impact of Run-of-River Hydro Schemes Upon Fish Populations, Final Report," Scotland and Northern Ireland Forum for Environmental Research, Edinburgh, UK, 2011.
7Turnpenny, A.W.H., and N. O'Keeffe, "Screening for Intakes and Outfalls: A Best Practice Guide. Science Report SC030231," The Environment Agency, Bristol, UK, 2005.
8Verrill, D.D., and C.R. Berry, "Effectiveness of an Electrical Barrier and Lake Drawdown for Reducing Common Carp and Bigmouth Buffalo Abundances," North American Journal of Fisheries Management, Vol. 15, 1995, pages 137-141.
9"Centrale Hydroelectrique de Vessy: Suivi du Système de Répulsion des Poissons (Suivi de Mise en Service)," GREN Biologie, Geneva, Switzerland. 2009.
10Holliman, F.M., "Operational Protocols for Electric Barriers on the Chicago Sanitary and Ship Canal: Influence of Electrical Characteristics, Water Conductivity, Fish Behavior and Water Velocity on Risk for Breach by Small Silver and Bighead Carp," Final Report U.S. Army Corps of Engineers, Cincinnati, Ohio, 2011.
11Swink, W.D., "Effectiveness of an Electrical Barrier in Blocking a Sea Lamprey Spawning Migration on the Jordan River, Michigan," North American Journal of Fisheries Management, Vol. 19, 1999, pages 397-405.
12Sparks, R.E., et al, "Evaluation of an Electric Fish Dispersal Barrier in the Chicago Sanitary and Ship Canal," American Fisheries Society Symposium, Vol. 74, Bethesda, Md., 2010, pages 121-137.
13"Operation of a Temporary Electrical Fish Barrier, San Joaquin River above the Confluence with the Merced River, Fall 1992," Project Report: State of California Department of Fish and Game, Inland Fisheries, Sacramento, Calif., 1993.
14Savino, J.F., D.J. Jude, and M.J. Kostich, "Use of Electrical Barriers to Deter Movement of Round Goby," American Fisheries Society Symposium, Vol. 26, Bethesda, Md., 2001, pages 171-182.
15Demko, D.B., S.P. Cramer, D. Neeley, and E.S. Van Dyke, "Evaluation of Sound and Electrical Fish Guidance Systems at the Wilkins Slough Diversion Operated by Reclamation District 108," Final Report: Cramer and Associates, Gresham, Ore., 1994.
16Barwick, D.H., and L.E. Miller, "Effectiveness of an Electric Barrier in Blocking Fish Movements," Production Environmental Services Research Report 90-07, Duke Power Company, Huntersville, N.C., 1990.
17"Post-Commissioning Ecological and Bathymetric Surveys at Beeston HEP Scheme: June-September 2003," Consultancy Report 383/03 for United Utilities PLC, Fawley Aquatic Research, Southampton, UK, 2003.
18Ostrand, K.G., W.G. Simpson, C.D. Suski, and A.J. Bryson, "Behavioral and Physiological Response of White Sturgeon to an Electrical Sea Lion Barrier System," Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science, Vol. 1, 2009, pages 363-377.
19"Hundreds of Steelhead Found Trapped in Dworshak Turbine Tube; about 1,000 Fish Killed," Columbia Basin Bulletin Weekly E-Mail Newsletter, Bend, Ore., Nov. 5, 2010.
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