22 - Low-head dams: A not-so clear and present danger

Hazards like "strainers," fallen trees and debris collecting between rocks and bridge piers that can trap floating objects, are generally conspicuous. And those familiar with the dynamics of moving water know how the force of the water, as it comes in contact with different obstructions, can actually hold objects.

Bridge piers and rocks are potentially dangerous basically because they don't move and the water does. If the water is moving fast enough, anything or anyone coming in contact with these structures can be held tight against their upstream side. Once pinned in this way, escape is difficult. We can easily understand the danger and what is happening when water holds an object against an obstacle.

However, the distinction is not so clear with the dangers associated with the river's most perilous obstruction, the low-head dam. It is a man-made structure, typically built to back up water in a reservoir for a variety of reasons. This wall-like structure pools the water as it flows over the crest and drops to the lower level.

This drop creates a hydraulic, which is a backwash that traps and recirculates anything that floats. Boats and people have been caught in this backwash. A person caught in the backwash of a low-head dam will be carried to the face of the dam, where the water pouring over it will wash him down under to a point downstream called the boil. The boil is that position where the water from below surfaces and moves either downstream or back toward the dam. A person who is caught in a low head dam struggles to the surface, where the backwash once again carries him to the face of the dam, thus continuing the cycle.

To complicate matters, these dams are usually loaded with debris, such as tires and logs on the surface and rocks and steel bars just below, posing additional problems should a person get trapped in this dangerous structure.

Dams do not need to have a deep drop to create a dangerous backwash. During periods of high water and heavy rains, the backwash current problems get worse, and the reach of the backwash current is extended downstream.

Small low-head dams that may have provided a refreshing wading spot at low water can become a brutal death trap when river levels are up. Simply put, it is not the drop of the dam which is the lethal danger, but the backwash current. This backwash current is governed by volume of water and flow.

From downstream, you may not realize the danger until it’s too late. From upstream, low-head dams are difficult to detect. In most instances, a low-head dam does not look dangerous, yet can create a life-threatening situation. You should always pay attention to warning signs, markers or buoys and keep well clear of low-head dams.

Low-head dams pose a serious danger to vessel operators. Surface currents below low-head dams can suck vessels toward the face of the dam. Currents above low-head dams can sweep vessels over the dam. The recirculating currents and turbulent waters below can swamp vessels and drown boaters.

Coroner says drownings at dam should be warning By William Presecky Tribune staff reporter Published July 13, 2006 The drownings of three men who became trapped in the "boil" beneath the Plamer Dam in Yorkville this spring underscore the potential for tragedy at all Fox River dams, Kane County Coroner Chuck West said Wednesday. West made his remarks after inquests in Geneva at which the May 27 deaths of kayaker Craig Fliege and his would-be rescuers, brothers Mark and Bruce Sperling, were ruled accidental by a coroner's jury In rendering its verdicts, the jury did not place blame for the accident or offer comments. But Fliege, 38, of Oakbrook Terrace, did not appear to have accidentally gone over the notoriously dangerous dam in his kayak, a state conservation police officer told the jury. "It is our belief that he knew the dam was there and he intentionally went over," said Illinois Department of Natural Resources police investigator William Bergland. Based on interviews and witness accounts of the accident, Bergland said investigators have little doubt Fliege ignored sign and marker buoys upstream warning of the upcoming dam. Bergland said witness Greg Freeman, owner of Freeman Sports in Yorkville, told him Fliege appeared to be paddling slowly near the edge of the dam before lining himself up, making a call on his cell phone and, after donning a life jacket, had attempted to "shoot" the dam close to where one of his friends was fishing downstream. Bergland said the bow of Fliege's kayak became wedged in submerged rocks and the stern was caught by the dam. Bruce Sperling, 32, of Lombard, and Mark Sperling, 27, of Yorkville were preparing to rent a canoe from Freeman just before the accident. When they asked Freeman what he was looking at through his binoculars, he responded, "I'm looking at a dead man," said Bergland. Bergland said Freemen immediately turned to call 911 while warning the Sperling brothers against going into the water near the dam to attempt a rescue. Both brothers were wearing life jackets, to no avail, said Bergland. It is not clear which brother went into the water first, he said. One was heard yelling: "That's my brother! That's my brother." "Once you are trapped in the boil of the dam, it is almost impossible to get out of," said Bergland. "Some people have survived [being trapped beneath the dam] but not many," he said. Yorkville Detective James Presnak, who also investigated the accident, told jurors that 18 people have drowned at the dam in the past 25 years. Some long-planned construction alterations of the so-called low-head dam that are designed to mitigate the dangerous boil were started soon after the drownings, he said. Although toxicology results showed Fliege had trace amounts of cocaine and marijuana in his system and Mark Sperling had trace amounts of marijuana and alcohol, there is no evidence any of the drowning victims was impaired, said Presnak. Although the accident occurred in Kendall County, all three men were pronounced dead at hospitals in Aurora, in Kane County. "It was a very tragic event that took three lives," said West.