A low head dam on a river is known as a drowning machine because it creates dangerous water conditions for boaters. These dams are often difficult to spot and can be deadly, especially during erratic flow times. Awareness campaigns are underway to tag or remove these dams.
A drowning machine is a name given to any low head dam on a river. A low-pressure dam is known as a drowning machine because it creates ideal water conditions for drowning unfortunate boaters. The drowning machine is, on most rivers, the most dangerous feature of a river and should be avoided at all costs.
When most people think of a dam, they think of a large wall that completely prevents water from continuing down the river. There may be some sort of release to allow the water to continue flowing, but it is usually well secured so boaters don’t get sucked into it. When you get to a large dam like this, you are usually on a large body of water and need to haul your boat around the area, or take a small channel or channel built specifically for boaters.
A headbutt dam, or drowning machine, however, allows water to move freely above the dam. While these types of dams can be easy to build and are an easy way to get water for irrigation, for the most part they were built when boating wasn’t such a popular pastime. For the average boater, the water rushing over the dam creates a particularly dangerous situation, for a variety of reasons.
As the water rushes over the top of this drowning machine, it hits the water at the bottom of the drop and creates a deep current that sweeps boaters down. As they begin to ascend, they are hit by the next cycle of water and are caught in a constant spin that keeps them underwater, disoriented, and repeatedly hit by the high forces of the water. It has often been noted that it would be difficult to design a more effective drowning machine on a river than low-head dams naturally create.
The drowning machine is especially dangerous because it can be very difficult to spot from the river. Since the actual dam may be a foot or more below water level, it may only look like a small rapid from a distance. While you assume that anywhere a drowning machine appears on a river it should be marked, there are thousands of unmarked low-rise dams across the country. For this reason it’s always a good idea to talk to someone familiar with the river before traveling it, to make sure there are no unsignposted hazards.
Boaters must also be very careful when traveling on a river during erratic flow times. After a meltdown in heavy rain or heavy snow, many dams that normally hold water completely can become flooded by particularly high water levels. This can turn a normally safe dam into a drowning machine. Along with strainers such as fallen tree limbs and logs that can also be melted during a storm, boating during heavy rains requires special caution.
Since the mid-1970s public awareness of the drowning machine phenomenon has increased dramatically. There are campaigns going on across the country to tag or remove existing low pressure dams and most river guides or rental spaces will have information on the locations of low pressure dams on any given river. With a little caution, the drowning machine shouldn’t be a particular hazard when underway, but it’s definitely worth looking out for.
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