The construction of numerous low-head dams altered North Dakota's rivers and streams over a century ago.

Originally intended for livestock watering, irrigation, water supply, and recreation, these seemingly benign structures conceal a sinister secret.

Known as "drowning machines," these low-head dams have claimed numerous lives, transforming tranquil waterways into death traps.

The Mechanism of Doom: How Low Head Dams Work

Low-head dams are typically simple concrete or rock-masonry structures that span the width of a river or stream.

Their purpose is to raise the water level behind them until it reaches a sufficient height to flow over the dam. However, this straightforward design masks a deadly danger.

Under the right conditions, the water flowing over the dam creates a "roller effect" on the downstream side, generating powerful recirculating currents. These currents can ensnare and drown unsuspecting boaters, swimmers, or other water users.

When water plunges over the dam, it forms a hydraulic jump at the base.

This turbulent water mixes with air, reducing buoyancy and making it nearly impossible for even strong swimmers to stay afloat. Life jackets, typically a source of safety, become less effective in these churning waters.

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The result is a deadly cycle of disorientation, hypothermia, exhaustion, and relentless battering by the water's force.

Drowning machines are so deadly, you are even advised to avoid trying to help someone who falls into one.

For a better look at how these drowning machines work, science commentator Kyle Hill put out a very in-depth and entertaining video describing the ins and outs of the deadly instance of fluid dynamics.

The Deceptive Calm: A False Sense of Security

One of the problems with these dams is that the level of danger can change depending on the flow conditions in the river.

Hazardous conditions may not exist at a dam all the time, potentially giving people a false sense of security. What may be a pleasant, inviting-looking place on one day can be very dangerous on another day under different conditions.

The Vicious Cycle of Death: Rescue Attempts Turn Tragic

Nationwide, a significant number of fatalities at low-head dams occur during rescue attempts.

Friends, family members, and even trained rescue personnel have been lured into the deadly grip of these structures while trying to save others.

The backflow currents and turbulence create a virtually inescapable circular trap, ensnaring would-be rescuers in a vicious cycle of doom.

Since 1900, there have been over 700 confirmed drownings at low-head dams, where drowning machines occur.

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Solutions and Mitigation Efforts: A Glimmer of Hope

Despite their deadly nature, low-head dams can be modified to reduce their danger. Options include removing the dam or altering it to eliminate hazardous conditions.

One effective solution is the installation of rock ramps. These gently sloping beds of rocks, strategically placed on the downstream side of the dam, create rapids instead of a sudden drop, eliminating the dangerous undertow and allowing fish to pass upstream.

As of 2018, 11 rock ramps have been implemented across North Dakota to subvert these deadly drowning machines. However, 51 low-head dams still exist across the state, posing a persistent threat to recreational river users.

As summer approaches and North Dakota's rivers beckon with promises of recreation and relaxation, it is imperative to remain vigilant.

The tranquil surface of a river can conceal the deadly force of a low-head dam. Awareness, caution, and respect for these structures can save lives.

Remember, the serene waters of today could become the drowning machines of tomorrow.

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