A drowning machine is a name given to any low-head dam on a river. A low-head dam is known as a drowning machine because it creates water conditions which are ideally for drowning hapless 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 blocks off water from continuing down the river. There may be some sort of release to allow water to keep flowing, but it is usually well protected so that boaters don’t get sucked through. When you come to a large dam like this, you’re usually in a big reservoir, and have to either portage your boat around the area, or else take a small canal or channel built expressly for boaters.
A low-head dam, or drowning machine, however, allows water to freely move over the top of the dam. Although these sorts of dam can be easy to put up, and are an easy way to get water for irrigation, for the most part they were built when boating was not as popular a past-time. For the average boater, the water flowing over the top of the dam makes for a particularly dangerous situation, for a number of reasons.
As 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 pulls boaters down. As they start to come up, they are hit by the next cycle of water, and are caught in a constant turning that keeps them below the water, disoriented, and repeatedly battered 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 particularly dangerous because it can be very difficult to spot from the river. Since the actual dam may be a foot or more below the water level, it may just appear to be a minor rapid from a distance. Although anywhere a drowning machine appears on a river is supposed to be marked, there are thousands of unmarked low-head dams throughout the country. For this reason, it’s always a good idea to talk with someone familiar with the river before traveling down it, to make sure there are no unmarked dangers.
Boaters also need to be very aware when traveling a river during irregular flow times. After a heavy rain or particularly heavy snow melt, many dams that normally would hold water back completely may be overrun by the especially high water levels. This can turn a normally safe dam into a drowning machine. Coupled with strainers like fallen tree branches and logs that may also be loosed during a storm, boating during heavy rain fall requires particular caution.
Since the mid-1970s the public awareness of the drowning machine phenomenon has increased markedly. There are campaigns in place throughout the country to mark or remove existing low-head dams, and most river guides or rental spaces will have information on the locations of low-head dams on a given river. With a little bit of caution, the drowning machine shouldn’t be a particular danger when boating, but it definitely bears watching out for.