Invasive Actions

There are pesky zebra mussels, quagga mussels, Eurasian ruffe and mud snails. There are spiny water fleas, spinier water fleas, stickle backs, round goby and tubnose goby.
And as more and more of them find their way out of foreign freighters’ ballasts, they pose a grave threat to the Great Lakes ecosystem, commercial shipping and the multi-million-dollar recreational boating industry.
Not to underrate their potential for destruction, but these nuisances are small fry compared to the fierce, four-foot-long, 70-plus-pound fish that’s making its way upriver toward Lake Michigan – escapees from Arkansas fish farms when they flooded in the 1990s. When agitated by boat engines, these behemoth big-head and silver carp have been known to leap 10 feet in the air, sometimes landing in boats and into the arms of shocked boaters.
According to Practical Fishkeeping magazine, boaters on Illinois, Missouri and Mississippi rivers “have suffered broken ribs, dislocated jaws, facial cuts and serious bruises” after being whacked by the leaping carp. In one instance, according to the Northwest Indiana Times’ Brendan O’Shaughnessy, “a jumping Asian carp smashed into the face of a jet skier … breaking her nose and leaving her unconscious in the water before she was rescued by another boat.”
Ground Zero
The Chicago Sanitary & Ship Canal is a manmade link between the Great Lakes and the Mississippi River, a busy transportation corridor for freight and recreational vessels. The canal and its tributaries also provide habitat for aquatic nuisance species swimming toward the Great Lakes from the Mississippi and vice versa. These invaders, particularly Asian carp, “consume huge amounts of plankton, knock out the bottom of the food chain and crowd out native species,” according to a Northwest Indiana Times article.
To combat the problem, the National Invasive Species Act of 1996 authorized $750,000 for the Army Corps of Engineers to study the effectiveness of a “dispersal barrier.” The expert panel considered sonics, bubble screens and thermal treatments, finally settling on an underwater electrified barrier.
“The barrier is not technically a fence or actual physical structure,” says Charles B. Shea, project manager for the Army Corps Chicago District. “It is a graduated electrical field in a column of water designed to make fish uncomfortable so they turn around and swim back to where they came from. At the same time, the barrier allows the unimpeded flow of water and boats.”
The first barrier was built in April 2002 as a demonstration project, he says, with a design life of three to five years – the primary limitation being the corrosion of electrodes. Based on the demo’s success, a permanent barrier was authorized and is currently under construction.
If the electrified water has its desired effect on fish, what about its effect on boaters and barges?
“The barrier has been operating safely for nearly five years,” Shea says. “Although the total output of the on-shore electrical equipment for Barrier II will be about 3,000 volts, this voltage is spread out over the entire electrified area in the water, as water is an almost perfect conductor.
“That’s a big area,” Shea continues, “as the canal is about 25-feet deep, and 160-feet wide, and the electrodes span over 480 feet of the canal length. Therefore, a fish or person in the water would not be exposed to anything near 3,000 volts, rather the typical field strength within the water at Barrier II will be about 1 volt/cm.”
Although the electric field may not totally incapacitate a person submersed in it, Shea says different people may react differently depending on their health. And the electric field would certainly make anyone in it quite uncomfortable.
“It is very important for boaters to be careful to avoid contact with the electrified water, although there is no possibility of electrocution because direct current (not AC) is used.”
To ensure that boats continue to safely transit the area, the Coast Guard recently issued specific procedures for vessels to follow when transiting the barrier site, such as mandatory use of PFDs, and rules about mooring, overtaking vessels and loitering.
There have been some reports of electrical arcing between barges and shore bollards.
“I haven’t heard of seeing arcing between ships and shore bollards,” says Shea. “Our preliminary testing did indicate that sparking is possible between metal boats and barges if they are not grounded together to maintain the same electrical potential. Sparks are not high voltage and pose minimal direct health risk, but could be a concern around flammable or explosive vapors or materials. The Coast Guard has issued its regulations to minimize the possibility of sparking.
“Safety is of paramount concern to the Corps. In fact, the Corps and the Coast Guard recently worked with the barge industry to develop and carry out safety tests at the Barrier I site. Lessons learned from those tests will be incorporated into the design of Barrier II.”