Thirteen years ago on April 17, 2007, two fire fighters were seriously injured while conducting water rescue training. The near miss occurred when they were practicing a two-boat tether rescue technique downstream of a low-head dam. Both boats being used in the evolution eventually crossed the boil line of the hydraulic created by the low-head dam, causing four fire fighters to become victims with two of them suffering serious injuries. For more details about this incident, read this NIOSH Report.
Photo of Low-Head Dam. Source: NIOSH
What is a low-head dam and a hydraulic?
Low-head dams are walls that span a river from one side to another that restrict the flow of water downstream. This causes a buildup of water upstream of the dam which can be used for recreational purposes. The problem with low-head dams, is that as the water flows over the top of the dam a dangerous phenomenon known as a hydraulic is created. Hydraulics are dangerous recirculating water that is highly aerated (in other words, has a lot of air in it). This recirculating water pulls in unsuspecting people and objects. Hydraulics can also be created by naturally occurring drops in rivers.
What is the two-boat tether technique and boil line?
The preferred method of performing a rescue of someone trapped in a hydraulic is from the shore using some type of reaching device or throw bag. A more advanced evolution utilizes two rescue boats tethered to each other. The primary or lead boat approaches the boil line from downstream while tethered to the secondary boat behind it. Once close enough, the primary boat can use a reach device or throw bag to perform the rescue from their boat. The secondary boat prevents the primary boat from being pulled into the hydraulic.
The boil line is the point you do not want to cross. The boil line is where the highly aerated recirculating water starts. Once passed the boil line, it is very difficult to escape the hydraulic. The recirculating water constantly pulls you back under the water, and the aerated water makes your personal flotation device highly ineffective. All of these factors together are why a lot of people call low-head dams “drowning machines.”
How many people have been killed by low-head dams?
Brigham Young University has done in-depth research on the dangers of low-head dams and maintains a database of reported fatalities. According to their data, there have been 555 fatalities since 1952. Unfortunately, several first responders have also been killed by low-head dams. Two of them, Captain Stanley Balsis and Firefighter Michael Whalen, are forever memorialized by their fire department in Elgin, IL.
Captain Balsis and FF Whalen Memorial. Source: Elgin Fire Department, Elgin, Illinois Facebook Page
Owner / Lead Instructor
Elder Technical Rescue Services, LLC
Mention this blog post when contacting us to set up a water rescue class for your agency and receive a 10% discount on the cost of the class!