There is a type of dam in Minnesota that's referred to as "drowning machines" or "killer dams" – and right now is when they're most dangerous.
Low-head dams (as they're known formally) account for more deaths than dam failures, according to the Minnesota Department of Natural Resources' "The Drowning Machine" report. And they're especially dangerous this time of year when there is high water runoff, the DNR notes.
What makes them so dangerous? The waters around them are strong enough to capsize a boat, and they can easily trap swimmers underwater, the DNR says.
The Associated Press says fatalities on low-head dams have spiked in recent years, which could be due to more people using the rivers and them being unaware of the dangers associated with these dams.
The Association of State Dam Safety Officials (ASDSO) found 211 fatalities have occurred since January 2000, and 91 since January 2010, with one-third of all deaths occurring in Iowa, Pennsylvania and Minnesota, reports note.
'Impossible to climb out'
"The builders of these dams have created a very elegant trap for human beings," Nate Hoogeveen, with Iowa Department of Natural Resources, told the AP. "Once people go over the dam, it's impossible to climb out."
As water pours over the dam it creates a churning backwash – also called a hydraulic jump or current – which recirculates the water. The DNR says:
"The roiling water takes any object — including a person — to the bottom of the stream, releases it to the surface, sucks it back to the face of the dam, and pushes it back to the bottom. This cycle can continue indefinitely."
In some cases, a life jacket won't even save a victim from drowning. About 45 percent of drowning victims at low-head dams were wearing a life jacket, reports show. Life jackets are one-third less buoyant when in aerated water, like near a dam, the DNR says.
The dams, which aren't typically more than 10-feet high, don't always look threatening and many are poorly marked, which can make them go unnoticed from upstream.
Not only is it dangerous for people using the rivers, but also for rescuers, the DNR notes. Specialized rescue techniques are often needed to pull victims from the river.
To stay safe and avoid these dams, Stan Linnell, the DNR's Boating and Water Safety Manager, told BringMeTheNews paddlers and other boaters should stick to the state water trails system or other designated waterways where hazards have been identified.
By the numbers
One of the most deadly is the Drayton Dam on the Red River between Minnesota and North Dakota, ASDSO notes. Between 1965-1995, 12 people were killed there.
The dam is located near a popular fishing area and isn't marked. The DNR has banned fishing within 150 feet of it.
Modifying for safety
Adding rock slopeways is one way officials are able to make these deadly dams safer, but the DNR says removal is the best way to enhance recreation safety.
Seven of the eight dams along the Red River have been retrofitted with rock slopeways, the DNR notes, but reminds they should still be considered dangerous.
In fact, dozens of dams around the state have been modified or removed to help curb drowning dangers, as well as increase the health of the waterway by allowing fish to move upstream, a 2005 report shows.
This is part of the DNR's ongoing effort to eliminate dams that don't have a purpose are are unsafe. Many of these were built in the late 1800s and early 1900s to provide water for grain mills or early hydroelectric generators, but over the years they weren't needed anymore.
But removing a dam can be a long and expensive process. Forum News says the owner of the dam has to agree to remove it, and then funding needs to be secured.
Removing a low-head dam can cost up to $1 million, the AP says.
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