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.