Danger Ahead: Low-Head Dams
They may not look dangerous, but mistaking low-head dams for recreational playspots is a potentially deadly miscalculation.
There's no better time than when the season of serious waterborne fun springs to life to start and continue a running conversation about playing it safe where running water and dangerous currents are concerned.
No talk about aquatic safety and the importance of threat-awareness around hydrological hazards is complete absent discussion of low-head dams and the dangers they pose to unwary swimmers and oblivious boaters.
Low-head dams and small “run-of-the-river” dams are impoundment structures, usually cement or stone, widely built across Eastern U.S. creeks and rivers in earlier times to power stone grain-grinding wheels or aid stream navigation and crop irrigation.
But even though technological advances have made most low-head dams obsolete, they're still a common sight along many navigable waterways.
Low-head dams are “designed and built such that water flows continuously over the crest from bank to bank,” according to the American Society of Civil Engineers, which has declared April “Low Head Dam Public Safety Awareness Month.”
“If water levels rise downstream, a submerged hydraulic jump can form which produces an upstream directed current that traps any recreationist who might go over the dam,” ASCE warns.
Low-head dams generate treacherous, churning currents at their base on the downstream side. These roiling danger zones can be powerful enough to capsize boats and enare even life jacket-wearing swimmers in a lethal, virtually inescapable maelstrom.
“Often referred to as ‘drowning machines,’ low-head dams are deadly because they produce dangerous recirculating currents, large hydraulic forces, low buoyancy and other hazardous conditions,” wrote Southeast Tennessee Tourism Association director Jenni Veal in a comprehensive 2019 article about the risks of the dams and ongoing efforts to alert the public of their presence. “Upon entering the ‘boil zone’ at the base of the dam, people and objects become trapped in the recirculating currents. Even life vests become less effective due to the reduced buoyancy.”
Dr. Bruce Tschantz, who for 37 years taught civil and environmental engineering students at the University of Tennessee, spent much of his career promoting safety around dams. Before his death in 2017, Tschantz tabulated more than 400 drowning deaths at low-head dams in 39 states since the 1960s.
Tales of drownings at low-head dams are always terrifying and tragic accounts of lost human potential -- the horror compounded by the fact that the deaths are entirely avoidable if river recreationists keep just this one thing in mind: avoid them entirely.
“The most important thing to remember is keep your distance, keep your life,” instructs DamSaftey.org, a website dedicated to educating people about the perils of waterway impoundments. “Steer clear of dam structures by recreating further up- or downstream, or portaging your kayak or canoe around the dam. Dams are not intended to be playgrounds, and pose many risks. Always be aware of your surroundings, know the location of dams, stay away from dams, and wear a personal floatation device such as a life jacket.”
Raising public concern about the menace low-head dams present is a fervent professional mission for Veal -- one she takes personally. It has in fact become something of an “obsession” for her. As someone who dedicates her career to heralding the wonder and beauty and vast recreational potential that her region of the planet offers the world, she feels morally inclined to alert people to areas where known dangers await.
A database developed and maintained by the Southeast Aquatic Resources Partnership has indexed and mapped more than 4,000 dams in Tennessee, 17,000 in Alabama and “an astounding 31,000 inventoried dams in Georgia,” according to Veal.
Experiencing nature in an intimate, firsthand manner brings with it certain natural dangers and risks to go with the naturally grand benefits and rewards.
Veal advises river-users to always “check river maps and ask locals for locations about dangerous structures before setting out on any unknown waterway.” Avoid approaching low-head dams from either the upstream or downstream side and pay attention to all public safety warning signs, takeout portages and boat barrier buoys, she says.
“The Southeast still has a ton of low-head dams, and there have been many deaths here and across the whole country because of them,” said Veal. “Especially as more and more people get their own boats to get out and explore our beautiful waterways, it is important to know that those dangers are there. If you don’t know if there is a low-head dam there, you could really be putting yourself or your family at risk.”