What Are Electric Barrier and Guidance Systems?
The electrical fish barrier can be thought of as an impassible barricade, and the fish guidance system as a repelling zone. Both consist of electrical current passing through water. The electrical circuit is made up of two or more metal electrodes submersed in water with a voltage applied between them. Electric current passing between the electrodes, via the water medium, produces an electric field. When fish are within the field, they become part of the electrical circuit with some of the current flowing through their body. The electric current passing through fish can evoke reactions ranging from a slight twitch to full paralysis, depending on the current level and shock duration they receive.
Types of Current
In the past, both Alternating Currents (AC) and Direct Current (DC) have been used to energize fish barrier and guidance systems; however, AC is known to be much more stressful to fish. Therefore, Smith-Root electrical fish barrier and guidance systems employ DC pulses of very short duration.
Electric Field Pattern
To produce the most efficient electric field pattern for blocking or guiding fish, it is desirable to produce a field with electric lines running head-to-tail along the fish. This orientation transfers the maximum power from water into the fish. In flowing water of one and one-half to two fish body lengths per second or greater, fish instinctively swim with their heads into the flow. Therefore, the most effective field pattern is one with the electric field lines running parallel to water flow. In sites with flowing water, Smith-Root electric fish barrier and guidance systems produce electric field lines which run parallel to water flow.
One of the most important advantages of the parallel field orientation is that when a fish is crosswise to the electric field it receives almost no electric shock. Fish learn very quickly that by turning side ways to the flow they can minimize the effects of the electric field. In this orientation, upstream migrating fish are swept clear of the field by water flow. The figure at right shows the typical reaction of migrating fish challenging an oriented electric field. In slow or static water a high percentage of fish also learn to turn in relation to the field and swim away from the electric field.
Graduated Fields
One of the most important features of the Smith-Root fish barrier design is the graduated electric field. As fish advance into a graduated field, they feel an increasingly unpleasant sensation. When the sensation is too intense, fish are unable to advance further and cannot keep their body orientated with the water flow. They turn perpendicular to the field, and are either swept clear by water flow or swim in the opposite direction from the increasing electric field.
How Is the Graduated Field Produced?
Smith-Root barrier and guidance systems use from two to six pulsators (pulse generators) to provide ascending levels of field intensity. The pulsators have their outputs connected to an array of evenly spaced electrodes placed across a stream bottom. Each pulsator can be adjusted to provide an increasing voltage between successive electrode pairs. This creates a gradually increasing electric field along the array. The pulsators are simultaneously triggered to cause the electric field lines to become additive and oriented with stream flow. Longer fish receive more head-to-tail voltage and are affected at an earlier stage, while smaller fish can penetrate the barrier further before being overcome or repelled.
The illustration at right shows a cross section of an electric field generated along a serially connected bottom-mounted electrode array. The oriented electric field causes the pattern to be distributed from the stream bottom to the surface.
Flush-Mounted Electrodes
Flush bottom-mounted electrode arrays do not alter normal water flow or catch debris. The electrodes are fixed into an insulating medium placed on the stream bottom. The insulating medium ensures that the electric current will flow through the water and not through the stream bottom.
For most permanent installations, the insulating medium is a special concrete mix called Insulcrete™. Site-specific designs include cast-in-place decks, precast flat panels, and precast culverts.
Plastic culverts are now also available. These provide the required insulation and allow flush-mounting of circular electrodes.
For site-evaluation we have portable canvas arrays that provide a temporary barrier system. The portable arrays are constructed of reinforced vinyl sheets with stainless steel cable electrodes attached to the top surface.
Smith-Root Upstream Fish Barrier systems are designed to totally block the passage of all upstream migrating fish. The barriers use electric pulses designed to partially paralyze fish without causing physical injury. The pulsators are adjusted to produce an ascending electric field sufficient to gradually reduce the ability of fish to swim against the water flow. It is best to have upstream barriers located in areas of medium to high water velocity in order to sweep stunned fish clear of the electric field. Often an attraction flow is provided just below a barrier to lure fish into hatcheries, traps, fish ladders, etc.
Upstream Barrier Hydraulics
For optimum design, it is important to maintain a uniform velocity and water depth across the entire water column. To do this, the bottom must be level and the sides should be contained. The bottom should also be smooth so that a velocity is maintained near the bottom. With high velocity and homogeneous flow throughout the barrier, inhibited fish are quickly swept clear of the electrified zone. For upstream migrating adult salmon and steelhead, our upstream electrical fish barriers have proven to work well in velocities ranging from 2 to 10 ft/sec.
Static Flow Barriers
Smith-Root static flow barrier systems are designed to startle and repel the advancement of migrating fish. The pulsator intensities are adjusted to provide a constant field strength across the array. The outputs are set to produce very narrow pulses with a slow repeating pulse rate. The narrow pulses do not tetanize or reduce fishes' ability to swim. The electrode array arrangement is similar to upstream barriers except parasitic electrodes are placed at each end to produce an abrupt field edge. The abrupt field edge causes fish to be startled toward open water. Tests have shown repelling efficiencies of nearly 100% in static flows when an open body of water is available for fish to return to.
Downstream migrating fish are instinctively attracted toward increasing water velocities, called attraction flows. The Smith-Root Downstream Guidance and Repelling systems are designed to guide downstream migrating fish away from dangerous attraction flows. Our design uses electrical pulses that do not tetanize fish or in any way reduce their swimming ability. Tetanized fish would be swept further into the electrified zone by water flow. To avoid the tetanizing effect, very short DC pulses are used which provide a sensation much like pins and needles. Repelled fish are guided towards an alternate waterway, with an attraction flow, or repelled toward open water, in the case of resident fish in a lake or reservoir.
Downstream Guidance Hydraulics
Downstream guidance systems should be located in areas of moderate water velocity and positioned well upstream from turbine intakes, pumps, etc. For downstream anadromous migration, an alternative attraction flow or bypass is required.
The best response is achieved when fish approach the electric field tail-first, as they typically will if the flow is at least 1 to 2 fish body length/sec. In addition, the electric field is designed to have an abrupt edge which increases the startle effect. The startle effect causes fish to dart ahead of the electrode array. To guide fish toward a bypass, the electrode array is often angled with relation to stream flow.
Once the fish have been guided into a bypass, it is essential to maintain a natural flow with uniform velocity well into the bypass so that fish will not reject it. Sudden increases in velocity within the bypass often spook downstream migrants, causing them to reject the bypass. For migrating Coho and Steelhead smolts, experimental tests indicate that velocities of 1 to 2 feet/sec work well. For Pinks, Chinook fry, and other small fish, somewhat lower velocities are desirable.
